Thèses sur le sujet « Protein amyloid fibril »

The aggregation of misfolded proteins into amyloid fibrils is implicated in the pathogenesis of several human degenerative diseases, including Alzheimer’s, Parkinson’s and Type II diabetes. Links between the deposition of amyloid fibrils and the progression of these diseases are poorly understood, with much of the current research focused on monomer misfolding and subsequent assembly of oligomers and mature fibrils. This project examines the formation of human apolipoprotein (apo) C-II amyloid fibrils, with a focus on the stability and reversibility of amyloid fibril assembly.
The initial stages of the project were to develop a model for apoC-II amyloid fibril formation. This was achieved by analysis of the concentration dependent kinetics of apoC-II amyloid fibril formation, and correlation of these data with the final size distribution of the fibrils, determined by sedimentation velocity experiments. On the basis of these studies, a new reversible model for apoC-II amyloid fibril formation is proposed that includes fibril breaking and re-joining as integral parts of the assembly mechanism. The model was tested by rigorous experimentation, with antibody-labelling transmission electron microscopy providing direct evidence for spontaneous fibril breaking and re-joining.
The development of this model for apoC-II fibril assembly provided the foundation for experiments to investigate factors that promote, inhibit or reverse amyloid fibril formation. Factors that were considered include a molecular chaperone protein, αB-crystallin, and a chemical modification, methionine oxidation. Investigations on the effect of αB-crystallin revealed that the inhibition of apoC-II fibril formation occurs by two distinct mechanisms: transient interaction with monomer preventing oligomerisation, and binding to mature fibrils, which inhibits fibril elongation. Studies on the effect of methionine oxidation on apoC-II fibril formation showed that both the assembly and stability of the fibrils was affected by this modification. ApoC-II contains two methionine residues (Met-9 and Met-60), and upon oxidation of these residues fibril formation was inhibited. In addition, the treatment of pre-formed fibrils with hydrogen peroxide caused dissociation of the fibrils via the oxidation of Met-60, located with the fibril core structural region. The final chapter details the development of antibodies that specifically recognise the conformation of apoC-II amyloid fibrils, which provide the foundation for future studies to examine the role that apoC-II amyloid fibrils play in disease.
Overall, this thesis reveals the dynamic and reversible nature of amyloid fibril formation. New insight is also obtained of the general stability of amyloid fibrils and the processes that may regulate their formation, persistence and disease pathogenesis in vivo.

Thesis (Ph.D.)--Tufts University, 2004.
Adviser: Eliana De Bernardez Clark. Submitted to the Dept. of Chemical Engineering. Includes bibliographical references (leaves 173-181). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Master of Science
Biochemistry and Molecular Biophysics
Jianhan Chen
Proteins are fundamental building blocks of life in an organism, and to function properly, they must adopt an appropriate three-dimensional conformation or conformational ensemble. In protein aggregation diseases, proteins misfold to incorrect structures that allow them to join together and form aggregates. A wide variety of proteins are involved in these aggregation diseases and there are multiple theories of their disease mechanism. However, a common theme is that they aggregate into filamentous structures. Therapies that target the process by which the aggregating proteins assemble into these similar fibril-like structures may by effective at countering aggregation diseases. This requires models that can accurately describe the assembly process of the fibrils. An analytical theory was recently described where fibrils grow by the templating of peptides onto an existing amyloid core and the kinetics of the templating process is modeled as a random walk in the backbone hydrogen bonding space. In this thesis, I present my work integrating molecular simulation with this analytical model to investigate the dependence of fibril growth kinetics on peptide sequence and other molecular details. Using the Aβ16-22 peptide as a model system, we first calculate the rate matrix of transitions among all possible hydrogen bonding microscopic states using numerous short-time simulations. These rates were then used to construct a kinetic Monte Carlo model for simulations of long-timescale fibril growth. The results demonstrate the feasibility of using such a theory/simulation framework for bridging the significant gap between fibril growth and simulation timescales. At the same time, the study also reveals some limits of describing the fibril growth as a templating process in the backbone hydrogen bonding space alone. In particular, we found that dynamics in nonspecifically bound states must also be considered. Possible solutions to this deficiency are discussed at the end.

The self-assembly of proteins into filamentous structures underpins many aspects of biology, from dynamic cell scaffolding proteins such as actin, to the amyloid plaques responsible for a number of degenerative diseases. Typically, these self-assembly processes have been treated as nucleated, reversible polymerisation reactions, where dynamic fluctuations in a population of monomers eventually overcome an energy barrier, forming a stable aggregate that can then grow and shrink by the addition and loss of more protein from its ends. The nucleated, reversible polymerisation framework is very successful in describing a variety of protein systems such as the cell scaffolds actin and tubulin, and the aggregation of haemoglobin. Historically, amyloid fibrils were also thought to be described by this model, but measurements of their aggregation kinetics failed to match the model's predictions. Instead, recent work indicates that autocatalytic polymerisation - a process by which the number of growth competent species is increased through secondary nucleation, in proportion to the amount already present - is better at describing their formation. In this thesis, I will extend the predictions made in this mean-field, autocatalytic polymerisation model through use of kinetic Monte Carlo simulations. The ubiquitous sigmoid-like growth curve of amyloid fibril formation often possesses a notable quiescent lag phase which has been variously attributed to primary and secondary nucleation processes. Substantial variability in the length of this lag phase is often seen in replicate experimental growth curves, and naively may be attributed to fluctuations in one or both of these nucleation processes. By comparing analytic waiting-time distributions, to those produced by kinetic Monte Carlo simulation of the processes thought to be involved, I will demonstrate that this cannot be the case in sample volumes comparable with typical laboratory experiments. Experimentally, the length of the lag phase, or "lag time", is often found to scale with the total protein concentration, according to a power law with exponent γ. The models of nucleated polymerisation and autocatalytic polymerisation predict different values for this scaling exponent, and these are sometimes used to identify which of the models best describes a given protein system. I show that this approach is likely to result in a misidentification of the dominant mechanisms under conditions where the lag phase is dominated by a different process to the rest of the growth curve. Furthermore, I demonstrate that a change of the dominant mechanism associated with total protein concentration will produce "kinks" in the scaling of lag time with total protein concentration, and that these may be used to greater effect in identifying the dominant mechanisms from experimental kinetic data. Experimental data for bovine insulin aggregation, which is well described by the autocatalytic polymerisation model for low total protein concentrations, displays an intriguing departure from the predicted behaviour at higher protein concentrations. Additionally, the protein concentration at which the transition occurs, appears to be affected by the presence of salt. Coincident with this, an apparent change in the fibril structure indicates that different aggregation mechanisms may operate at different total protein concentrations. I demonstrate that a transition whereby the self-assembly mechanisms change once a critical concentration of fibrils or fibrillar protein is reached, can explain the observed behaviour and that this predicts a substantially higher abundance of shorter laments - which are thought to be pathogenic - at lower total protein concentrations than if self-assembly were consistently autocatalytic at all protein concentration. Amyloid-like loops have been observed in electron and atomic-force microscographs, together with non-looped fibrils, for a number of different proteins including ovalbumin. This implies that fibrils formed of these proteins are able to grow by fibrillar end-joining, and not only monomer addition as is more commonly assumed. I develop a simple analytic expression for polymerisation by monomer addition and fibrillar end-joining, (without autocatalysis) and show that this is not sufficient to explain the growth curves obtained experimentally for ovalbumin. I then demonstrate that the same data can be explained by combining fibrillar end-joining and fragmentation. Through the use of an analytic expression, I estimate the kinetic rates from the experimental growth curves and, via simulation, investigate the distribution of lament and loop lengths. Together, my findings demonstrate the relative importance of different molecular mechanisms in amyloid fibril formation, how these might be affected by various environmental parameters, and characteristic behaviour by which their involvement might be detected experimentally.

Functional amyloids found throughout nature have demonstrated that amyloid fibers are potential industrial biomaterials. This work introduces a new 'template plus adder' cooperative mechanism for the spontaneous self-assembly of micrometer sized amyloid fibers. A short hydrophobic template peptide induces a conformation change within a highly α-helical adder protein to form β-sheets that continue to assemble into micrometer sized amyloid fibers. This study utilizes a variety of proteins that have template or adder characteristics which suggests that this mechanism may be employed throughout nature. Depending on the amino acid composition of the proteins used the mixtures form amyloid fibers of a cylindrical (~10 μm diameter, ~2 GPa Young's modulus) or tape (5-10 μm height, 10-20 μm width and 100-200 MPa Young's modulus) morphology. Processing conditions are altered to manipulate the morphology and structural characteristics of the fibers. Spectroscopy is utilized to identify certain amino acid groups that contribute to the self-assembly process. Aliphatic amino acids (A, I, V and L) are responsible for initiating conformation change of the adder proteins to assemble into amyloid tapes. Additional polyglutamine segments (Q-blocks) within the protein mixtures will form Q hydrogen bonds to reinforce the amyloid structure and form a cylindrical fiber of higher modulus. Atomic force microscopy is utilized to delineate the self-assembly of amyloid tapes and cylindrical fibers from protofibrils (15-30 nm width) to fibers (10-20 μm width) spanning three orders of magnitude. The aliphatic amino acid content of the adder proteins' α-helices is a good predictor of high density β-sheet formation within the protein mixture. Thus, it is possible to predict the propensity of a protein to undergo conformation change into amyloid structures. Finally, Escherichia coli is genetically engineered to express a template protein which self-assembles into large amyloid fibers when combined with extracellular myoglobin, an adder protein. The goal of this thesis is to produce, manipulate and characterize the self-assembly of large amyloid fibers for their potential industrial biomaterial applications. The techniques used throughout this study outline various methods to design and engineer amyloid fibers of a tailored modulus and morphology. Furthermore, the mechanisms described here may offer some insight into naturally occurring amyloid forming systems.
Ph. D.

Under particular conditions proteins spontaneously aggregate into well-ordered structures called amyloid fibrils. The full elucidation of the fibrillation process requires the identification by biophysical techniques of the conformational and oligomeric species populated during the aggregation mechanism.

De nombreux systèmes biologiques sont intrinsèquement polydispersés, présentant de multiples espèces coexistantes, de taille, de forme ou de conformation différentes (c'est-à-dire, mélanges oligomèriques, des complexes faiblement liés se dissociant en composantes individuelles ou des espèces apparaissant lors de processus amyloïdogéniques). L'étude de tels systèmes complexes est une tâche difficile en raison de l'instabilité des espèces concernées, de leurs concentrations relatives faibles et interdépendantes et des difficultés rencontrées pour l'isolation des composantes pures. Dans cette thèse, j'ai développé des approches méthodologiques pour appliquer la diffusion des rayons X aux petits angles (SAXS), une technique de biologie structurale, à l'étude de systèmes polydispersés. SAXS est une technique additive et par conséquent, le diagramme de diffusion mesuré pour un échantillon polydispersé correspond à la somme pondérée en concentration des contributions de chacune des composantes individuelles du mélange. Cependant, la décomposition des données de SAXS en des spectres spécifiques des espèces et de leurs concentrations relatives est extrêmement laborieuse et ambigue. Dans cette thèse, je présente d'abord une approche objective pour solidement décomposer les jeux de données de SAXS en composantes individuelles. Cette approche adapte la méthode chimiométrique « Multivariable Curve Resolution Alternate Least Squares » (MCR-ALS) aux spécificités des données de SAXS. Notre méthode permet une décomposition rigoureuse et robuste des données de SAXS en introduisant simultanément différentes représentations de ces données et par conséquent, en mettant l'accent sur des changements moléculaires à différentes plages de temps et de résolution structurale. Nous avons appliqué cette approche, que nous appelons COSMiCS (Analyse structurelle objective complexe des systèmes multi-composants) pour étudier deux systèmes polydispersés: la fibrillation des protéines, et les fluctuations conformationnelles de protéines grâce à l'analyse de données obtenues à l'aide d’une technique de couplage de chromatographie d'exclusion de taille (SEC) avec le ligne de SAXS (SEC-SAXS). L'importance d'étudier les processus de fibrillation réside dans leur implication dans des pathologies amyloïdogéniques telles que les maladies de Parkinson ou d'Alzheimer. Il existe de fortes indications que les espèces oligomériques solubles, et non les fibrilles matures, sont la cause principale de la cytotoxicité et des dommages neuronaux. Cette observation souligne l'importance de caractériser les premiers stades des processus de fibrillation. Notre approche COSMiCS a permis d'étudier les processus amyloïdogéniques de l'insuline et du mutant familial E46K de l'α-synucléine, une protéine associée à la maladie de Parkinson. Cette analyse permet la caractérisation structurale des espèces présentes (y compris les espèces oligomériques) et la caractérisation cinétique de leurs transformations.La deuxième partie de la thèse est consacrée à l'utilisation de COSMiCS pour analyser des données de SEC-SAXS. Le SEC-SAXS est extrêmement populaire et a été implémenté sur plusieurs lignes de SAXS à travers le monde. En utilisant des données synthétiques, je démontre la capacité des approches chimiométriques à décomposer des profils chromatographiques complexes. À l'aide de cette approche, j'ai décomposé l’ensemble des données SEC-SAXS mesurés pour la Prolyl OligoPeptidase (POP).En résumé, cette thèse présente une nouvelle approche chimiométrique qui peut être généralement appliquée à tout mélange macromoléculaire pouvant subir une modifacation de son équilibre et pouvant être abordé par SAXS. Les complexes biomoleculaires transitoires, les processus de repliement, les réarrangements structuraux dépendants d’un ligand ou la formation de grands ensembles supramoleculaires peuvent être sondés de façon structurale en utilisant l'approche COSMiCS
Many biological systems are inherently polydisperse, presenting multiple coexisting species differing in size, shape or conformation (i.e. oligomeric mixtures, weakly bound complexes, and species appearing along amyloidogenic processes). The study of such complex systems is challenging due to the instability of the species involved, their low and interdependent relative concentrations, and the difficulties to isolate the pure components. In this thesis, I have developed methodological approaches to apply Small-Angle X-ray Scattering (SAXS), a low-resolution structural biology technique, to the study of polydisperse systems. As an additive technique, the SAXS pattern measured for a polydisperse sample corresponds to the concentration-weighted sum of the contributions from each of the individual components. However, decomposition of SAXS data into species-specific spectra and relative concentrations is laborious and burdened by ambiguity. In this thesis, I present an approach to decompose SAXS datasets into the individual components. This approach adapts the chemometrics Multivariate Curve Resolution Alternating Least Squares (MCR-ALS) method to the specificities of SAXS data. Our method enables the rigorous and robust decomposition of SAXS data by simultaneously introducing different representations of these data and, consequently, emphasizing molecular changes at different time and structural resolution ranges. We have applied this approach, which we name COSMiCS (Complex Objective Structural analysis of Multi-Component Systems), to study two polydisperse systems: amyloid fibrillation by analysing time-dependent SAXSdata, and conformational fluctuations through the analysis of data obtained using on-line size-exclusion chromatography coupled to SAXS (SEC-SAXS). The importance of studying fibrillation processes lies in their implication in amyloidogenic pathologies such as Parkinson’s or Alzheimer’s diseases. There exist strong indications that soluble oligomeric species, and not mature fibrils, are the main cause of cytotoxicity and neuronal damage emphasizing the importance of characterizing early stages of fibrillation. The first application of our COSMiCS approach has allowed the study of the amyloidogenic mechanisms of insulin and the familial mutant E46K of ↵-synuclein, a Parkinson’s disease related protein. The analysis enables the structural characterization of all the species present as well as their kinetic transformations. The second part of the thesis is dedicated to the use of COSMiCS to analyze on-line SEC-SAXS experiments. Using synthetic data, I demonstrate the capacity of chemometric approaches to decompose complex chromatographic profiles. Using this approach, I have studied the conformational fluctuations in prolyl oligopeptidase (POP), a protein related to synaptic functions and neuronal development. In summary, this thesis presents a novel chemometrics approach that can be generally applied to any macromolecular mixture with a tuneable equilibrium that is amenableto SAXS. Transient biomolecular complexes, folding processes, or ligand-dependent structural rearrangements can be probed structurally using COSMiCS

This thesis explores the complex relationship between food protein structure and digestibility. Food proteins are important nutrients that play a central role in controlling the textural properties of many foods. Processing of food proteins may alter the protein aggregate structure and digestibility. The degree of protein aggregation during food processing depends on the denaturing conditions and the presence of other food components. Sugars and lipids may contribute to protein glycation and protein cross-linking via the Maillard reaction. Furthermore, amino acid residues of food proteins may be chemically modified during processing, thereby influencing both the structure and the nutritional value of proteins. An in vitro digestibility assay was used to investigate the relationship between protein aggregate structure and protein digestibility. Raw and boiled egg whites were exposed to a wide range of conditions: pH 2 - 12, in the presence and absence of 200 mM NaCl. It was found that pH and NaCl treatment prior to in vitro digestion resulted in significantly different protein ultrastructures, but did not markedly influence protein digestibility under the tested conditions. Raw egg white was less digestible than boiled egg white under all test conditions. The inclusion of Maillard reaction partners caused protein cross-linking concurrent with a decrease in digestibility. The digestibility decreased with the reactivity of the Maillard reaction partner and with increasing heating time. Proteomic analysis, using tandem mass spectrometry, of raw and heated egg white showed an increase in hydrothermally induced amino acid modifications. In the presence of glucose and methylglyoxal, a Maillard reaction specific increase in arginine modification to hydroimidazolone was observed with increasing heating times. The observed modifications are likely to contribute to a change in the nutritional quality of egg white. Aggregation kinetics of the major egg white protein, ovalbumin, were studied by dynamic light scattering, small angle X-ray scattering, and transmission electron microscopy. Shape determination was only possible for ordered aggregates, but not for disordered aggregates. Prior to heating, ovalbumin molecules in the presence of water and glucose repelled each other in concentrated solution. The presence of NaCl shielded electrostatic repulsion, leading to early onset dimerisation and disordered aggregation upon heating. Methylglyoxal treated ovalbumin formed more ordered aggregates. The scattering of these structures was able to be fitted to cylindrical shape models showing an increase of cylinder length with time while the cylinder diameter remained near constant over 24 hours of heating. In addition, food protein derived amyloid fibril aggregates were characterised. Amyloid fibrils are a common ordered protein fold that has been linked to neurodegenerative diseases. In the recent literature, amyloid fibrils have been proposed as new functional macromolecules in proteinaceous foods because of their desirable textural properties. Food fibrils formed from whey, egg white, soy bean and kidney bean protein were tested to establish whether they are protease resistant or display toxicity to human Caco-2 cells (a model intestinal cell line). The food fibrils were compared to insulin amyloid fibrils, a well characterised amyloid system. It was shown that the food fibrils displayed some resistance towards in vitro hydrolysis and were not found to be toxic. This work contributes to the understanding of food protein aggregation and digestibility under relevant conditions. It highlights the relationship of aggregate structure and digestibility and the particular role of the Maillard reaction. Moreover, evidence is provided that food protein derived amyloid fibrils may be safe ingredients in consumables. These findings may contribute to optimising industrial food processes and creating safe new food products.

Alzheimer’s disease (AD) is the most common cause of senile dementia worldwide. AD is a neurodegenerative disorder characterized by the loss of memory and language skill, collapse of the cognitive function, and distortion of social behavior. As of today, the onset mechanisms of AD and cure are unknown; however, three hallmarks are commonly encountered: extra and intracellular accumulation of amyloid beta (A!) peptide plaques, formation of intracellular neurofibrillary tangles, and inevitable neuronal death. Hypothetically, a possible scenario provoking or involved in the onset of AD is a cascade effect that starts with an imbalance in the production and clearance of Aß peptide that consequently leads to its accumulation, formation of tau protein tangles and neuronal death. This work studied and characterized the mechanisms governing A! peptide aggregation and the effects of using anti-Aß monoclonal antibodies to modify this process. These mechanisms play an important role in the formation of AD plaques and are critical in the search for therapies involving Aß peptide plaque clearance. Yet, antibody-based therapies for plaque clearance are not well understood, adding to the existing concerns about side effects in humans, hence there is a necessity of knowledge in this matter. In this work different Nterminus, C-terminus, and Mid-domain antibodies were used against Aß peptide species (monomers, oligomers, and fibrils) to probe peptide aggregates modification and disruption. Additionally, construction of a soft supported lipid bilayer membrane was proposed to study the adhesion mechanisms of Aß peptide and interactions with antibodies, mimicking the neuronal cell surface. The main characterization techniques used in this work were: atomic force microscopy (AFM) and transmission electron microscopy that allowed the physical exploration and visualization of the different processes of aggregation in terms of adhesion, size evolution, and distribution of the peptide; and attenuated total reflectance Fourier spectroscopy (ATR/FTIR) which allowed monitoring the change of secondary structures for the peptide during the processes studied. It is endeavored that this work will help to elucidate the effects attributed to the molecular interactions between A! peptide species and antibodies to target Aß plaque’s clearance in the brain of AD patients. Ultimately, this study provides novel information critical for the formulation of effective therapies to prevent and treat AD with less collateral effects. It also represents a contribution to the basic scientific knowledge regarding peptide-antibody interactions with application to other diseases related to protein misfolding.

Self-assembly of biomolecules into beta-sheet structures can be applied in the creation of nano-materials with novel electrical, optical, catalytical, or/and mechanical characteristics. This work was directed towards the construction of nano-derivatives based on amyloid fibrils forming proteins (Abeta40 peptide, a-Synuclein (a-Syn), equine lysozyme (EL)). Such nanostructures can be used to produce nanoscale functional systems. Herein, different mutant and hybrid proteins, which were able to form fibrillar structures, were constructed and the properties of fibrils were investigated. Designed cysteine mutants of Abeta40 and a-Syn can be modified through thiol group of cysteine. Herein, for the first time, it was demonstrated that a-Syncys141 fibrils could be modified with biotin and gold nanoparticles with neutravidin molecules. Hybrid proteins of Abeta40 or a-Syn and other non-amyloid proteins were designed on purpose to obtain fibrils with active functional non-amyloid proteins. Under appropriate conditions, these proteins aggregated into beta-sheet structures. Hybrid protein of streptavidin and Abeta40 formed a net-like fibrillar structure, and streptavidin was active. For the first time it was described the production of recombinant EL in E. coli. Moreover, active EL can form fibrils, which are similar to the fibrils formed by native EL. Constructed novel hybrids and mutants that are able to form amyloid fibrils, can be applied for the creation of functionalized nanodevices... [to full text]
Savitvarkės biomolekulės, gebančios formuoti beta-klosčių struktūras, gali būti pritaikomos nanomedžiagų su naujomis elektrinėmis, optinėmis, katalitinėmis ir/ar mechaninėmis savybėmis, kūrimui. Šiame darbe buvo siekiama kurti nanodarinius, grįstus amiloidines fibriles formuojančiais baltymais (Abeta40 peptidas, a-sinukleinas (a-Syn), kumelės pieno lizocimas (EL)), kurie būtų pagrindas nano dydžio funkcinių sistemų gamybai. Šiam tikslui buvo sukonstruoti mutantiniai ir hibridiniai baltymai bei tiriamos jų fibrilinių struktūrų savybės. Sukurti Abeta40 ir a-Syn cisteino mutantai, kurie gali būti modifikuojami per cisteino tiolinę grupę. Pirmą kartą buvo pademonstruotas a-Syncys141 baltymo fibrilių modifikavimas biotinu ir aukso nanodalelėmis su neutravidinu. Sukonstruoti hibridiniai baltymai, kurie sudaryti iš Abeta40 ar a-Syn bei GDH, streptavidino ir hidrofobino. Buvo tikimasi, kad tokie baltymai formuos fibrilines struktūras, o funkciniai baltymai bus aktyvūs. Esant atitinkamoms sąlygoms, šie baltymai agregavo suformuodami skirtingos morfologijos beta-klostines struktūras. Streptavidino ir Abeta40 hibridinis baltymas formavo fibrilinę struktūrą – tinklą, o streptavidinas buvo aktyvus. Šiame darbe pirmą kartą aprašoma rekombinantinio EL gamyba E. coli ląstelėse. Aktyvus EL gali formuoti panašias į natyvaus EL fibrilines struktūras. Sukonstruoti nauji hibridiniai ir mutantiniai baltymai, gebantys formuoti amiloidines fibriles, yra geras pagrindas, kuriant funkcionalizuotus... [toliau žr. visą tekstą]

Protein-based materials are an important area of research for various reasons. Natural protein materials such as spider silk have mechanical properties which compare favourably to artificial or inorganic materials, and in addition are biodegradable and can be produced from easily available feedstocks. It is also possible to produce materials that incorporate the functionality of a natural protein, such as ligand-binding or catalysis of reactions, thus allowing this functionality to be used in the solid rather than solution phase. Two particularly interesting components for protein-based materials are amyloid fibrils and tandem repeat proteins. Amyloid fibrils are exceptionally strong, tough, highly-ordered structures that self-assemble from a wide range of simple building blocks. Meanwhile, tandem repeat proteins are a class of proteins that act as scaffolds to mediate protein-protein interactions and are known to act as elastic springs. Unlike globular proteins, tandem repeat proteins can be designed to bind specific ligands, and their ligand-binding properties and stability can be tuned separately. This work details the synthesis and characterisation of repeat protein and amyloid fibril components for a “smart” hydrogel, the production of these gels, and their characterisation using a microfluidic method that I developed. Although amyloid fibrils have previously been decorated with functional proteins, hitherto, this has usually been done by assembling the fibrils from already-functionalised components. This approach limits the functionality to species that can survive the harsh conditions of amyloid aggregation and do not disturb fibril assembly. Therefore, a method was developed to produce amyloid fibrils that displayed an alkyne functionality on their surface to allow functional proteins or other species to be attached after assembly. This involved the design and synthesis (using solid-phase peptide chemistry) of a peptide based on the previously known TTR105-115 peptide (derived from the amyloidogenic Transthyretin protein). These fibrils were characterised by AFM and TEM and it was then shown that the assembled fibrils could be functionalised using an azide-alkyne “click” reaction. The reaction was shown to work with a variety of ligands including proteins, which were found to retain their structure and function after crosslinking to the fibril. The fibrils with ligands attached were characterised by a variety of methods including LCMS (liquid chromatography-mass spectrometry) and super-resolution optical microscopy. Next, repeat proteins were produced recombinantly containing non-natural azido amino acids at their termini. Incorporation of non-natural amino acids was carried out using a number of different methods including amber codon suppression and methionine replacement. Micron-sized hydrogels were then formed from microfluidic-generated droplets by covalently crosslinking the alkyne-functionalised fibrils with the azide-functionalised repeat proteins. The initial experiments to show proof of principle were carried out with consensus-designed repeat proteins, but repeat proteins based on natural sequences were also used to make hydrogels that could later be tested for potential uptake of peptides known to bind these proteins. These hydrogels could potentially be used for drug delivery or other applications in which a chemical response to a mechanical stimulus is desired. The mechanical properties of the hydrogels were measured using novel microfluidic devices, which were designed and fabricated using standard PDMS-based soft lithography.

The current landscape of nanotechnology has focussed attention on materials that self-assemble. The search for such materials has unsurprisingly led to the biological world, where functional nanoscale biomolecular assemblies are in abundance. Amyloid fibrils are one such self-assembling biological structure, formed when native proteins misfold into insoluble fibrous quaternary structures. This research has explored the use of amyloid fibrils formed from waste proteins, namely crude crystallin proteins from fish eye lenses, as biological nanowires. The use of amyloid fibrils as nanowires was investigated by examining the ability to control their dimensions and arrangement, along with analysis of their properties, such as stability and conductivity. TEM and AFM studies on the model amyloid forming protein, bovine insulin, showed that a number of fibril length distributions can be achieved, by systematically altering fibril growth and storage conditions. Although the same set of conditions cannot be directly applied to crystallin fibrils, these fibrils can also be produced on a range of length scales. Amyloid fibrils can be manipulated and aligned in a controlled manner by dielectrophoresis; this tool could later be used to incorporate amyloid fibrils into a biosensing or bioelectronics device. Dielectrophoresis was also used to immobilise crystallin fibrils between electrode pairs, in order to investigate the conductivity of small numbers of fibrils. These experiments complemented work carried out on the conductivity of amyloid fibril networks, using fabricated interdigitated electrodes. In the unmodified state, amyloid fibrils formed from bovine insulin, fungal hydrophobins, and crude crystallins were all shown to have low conductivity, with current values in the range of 10⁻⁸–10⁻¹⁰ A recorded at bias voltages of 0–2 V. Amyloid fibrils were used as a template for the synthesis of conductive nanowires, by modification with the conducting polymers polyaniline and polypyrrole, increasing conductivity by one and four orders of magnitude respectively. The functionalisation of fibrils with glucose oxidase enabled the creation of a very simple glucose sensing device. This device, consisting of a gold electrode modified with the glucose oxidase functionalised fibrils, showed an electrochemical response in the presence of glucose and the mediator FcOH. Future work is necessary to optimise the use of amyloid fibrils in this way; however, this study confirms a role for amyloid fibrils from a low cost source in bionanotechnology.

Amyloid fibrils are a misfolded state formed by many proteins when subjected to denaturing conditions. Their constituent amino acids make them an excellent target for enzyme immobilisation and their strength, stability and nanometre size are attractive features for exploitation in the creation of new bionanomaterials. The aim of this thesis was to functionalise amyloid fibrils by conjugation to glucose oxidase (GOD). GOD is a relatively stable glycoprotein that catalyses the oxidation of glucose and the release of hydrogen peroxide. The consumption of glucose can be measured to assess glucose levels, and the release of hydrogen peroxide is cytotoxic to cells and is thus an effective antibacterial agent. Three methods of attachment were used: cross-linking using glutaraldehyde, periodate oxidation of the glycoprotein shell, and cross-linking using glutaraldehyde following deglycosylation. GOD retained activity upon attachment by all three methods. These attachment methods were assessed using electrophoresis, centrifugation, sucrose gradient centrifugation and TEM. Gel electrophoresis indicated a high degree of cross-linking and TEM showed no significant change of fibril morphology upon cross-linking. Centrifugation experiments suggested a non-covalent interaction was occurring between amyloid fibrils and GOD, and a covalent attachment was occurring upon addition of glutaraldehyde. Sucrose gradient centrifugation provided increased separation of cross-linked material compared to other separation methods, and showed greater cross-linking to crystallin amyloid fibrils than insulin fibrils. Cross-linking native GOD using glutaraldehyde was chosen for further experiments, as it was found to be most effective for GOD attachment to amyloid fibrils. The resulting functionalised enzyme scaffold was then incorporated into a model poly(vinyl alcohol) (PVOH) film, to create a new bionanomaterial. The distribution of the functionalised fibrils through the film was characterised using SEM and confocal microscopy, where film components were found to be unevenly dispersed. The antibacterial effect of the functionalised film was then tested on E. coli and the antifungal effect of the film was tested on Fusarium, Rhizopus and Penicillium. Growth of E. coli was inhibited around functionalised film circles, demonstrating the incorporation of GOD antibacterial activity into the PVOH film. However, no growth inhibition of fungal species was observed. This work is of significance as it demonstrates the ability to convert a waste material, bovine lens crystallin, to high value protein nanofibres and incorporate functionality via GOD attachment. The incorporation of the GOD-functionalised amyloid fibrils into PVOH provides an excellent ‘proof of concept’ model for the creation of a new bionanomaterial using a functionalised amyloid fibril scaffold. Future development of this model system has the potential to lead to the production of a novel biomaterial for use in food packaging due to the antimicrobial properties of GOD.

Protein nanofibres, commonly known as amyloid fibrils, are emerging as potential biological nanomaterials in a number of applications. Protein nanofibres are a highly ordered insoluble form of protein, which results when a normally soluble protein aggregates via a self-association process. However, researchers are currently faced with several challenges such as finding a cheap source of proteins that can be obtained without expensive purification and optimizing a scalable method of the manufacturing of protein nanofibres. This thesis has identified crude mixtures of fish lens crystallins as a cheap protein source and has optimized methods for large scale production of protein nanofibres of varying morphologies. Results show that by varying the conditions of fibre formation, individual protein fibres can be used as building blocks to form higher order structures. This ability to control the morphology and form higher ordered structures is a crucial step in bottom up assembly of bionanomaterials and opens possibilities for applications of protein nanofibres. The method of formation of protein nanofibres was optimized on a bench scale (1.5 mL Eppendorf tubes) and successfully scaled-up to 1 L volume. For larger scale-up volume (i.e. greater than 10 ml), internal surface area was important for the formation of protein nanofibres. The crude crystallin mixture prepared at 10 mg/mL was heated at 80oC in the presence of 10% v/v TFE at pH 3.8 for 24 hours and stored for an additional of 24 hours at room temperature for storage process. Aggregation and precipitation of proteins were observed as the protein solution was added to the pre-heated TFE. The resulting protein nanofibres were characterised using ThT dye binding, TEM and SEM. The TEM images show a network of long and criss-crossing protein nanofibres with individual fibres of approximately 10 to 20 nm in diameter and 0.5 to 1 μm long. These protein nanofibres were prepared in 1 mL centrifuge tubes and were left on the laboratory bench at room temperature. After 5 months, fresh TEM grids of the sample were prepared and visualized using TEM. Interestingly, TEM images show that a number of individual fibres had self-assembled in an intertwining fashion to form large bundles and higher order structures containing bundles of nanofibres up to 200 nm thick.

Current interest in studying amyloid fibrils arises from their involvement in different fields (Chiti and Dobson, 2006). First, they play a crucial role in disorders such as Alzheimer's and Parkinson's diseases. Second, since it has been demonstrated that all polypeptide chains form fibrils under appropriate conditions, the understanding of why and how this process happens has become central problem in protein knowledge. Last, the ordered ultrastructure characterizing amyloid fibrils may be thought as a basis for nanomaterials with possible technological applications. However, despite the ability of most proteins to form amyloid fibrils, very little is known about their structures and the factors that govern their formation. The process of amyloid formation requires the partial unfolding of protein molecules into such conformations able to interact to each others and reorganize into well-ordered structured aggregates, named amyloid fibrils. In this Thesis the amyloid formation by globular proteins has been analyzed from different points of view, focusing in the first part of the research work on the elucidation of some conformational features promoting protein aggregation. The second part was concentrated on the characterization of the final supramolecular structure of amyloid fibrils. In order to study the partially folded state, two globular proteins have been analyzed, alpha-lactalbumin (LA) and HypF-N. Indeed, under specific conditions, these proteins populate a not fully folded state previously shown to play an important role in the amyloid formation (Uversky, 2002; Chiti et al., 2001). The study conducted on LA has been based on the effects of the proteolytic dissection of the molecule on its conformational features and aggregation properties. It was previously shown that LA is able to form fibrils morphologically indistinct from the pathological ones (Uversky et al., 2002). Here, we have studied the aggregation propensities of LA derivatives characterized by a single peptide bond fission (1-40/41-123, named Th1-LA) or a deletion of a chain segment of 12 amino acid residues located at the level of the ?-subdomain of the native protein (1-40/53-123, named des?-LA). We have also compared the early stages of the aggregation process of these LA derivatives with those of intact LA. The main conclusion of this work was that the inherent flexibility of the LA derivatives allows the large conformational changes required to form the cross-?-structure of the amyloid fibrils. It has been emphasized that proteolysis can be considered a causative mechanism of protein aggregation and fibrillogenesis (Polverino de Laureto et al., 2005). In the other case, the conformational characterization of an amyloidogenic state of HypF-N has been performed at acid pH, in order to allow the protein to populate a partially unfolded ensemble. Combining different biophysical and biochemical techniques, it has been shown that this partially unfolded structure has all the hallmarks of a pre-molten globule state, i.e. it is more compact than a random coil-like state but less organized than a native-like intermediate or a MG state (Uversky, 2002). Furthermore, it is shown that a modulation of the total ionic strength of the solution allows enhancing the apparent rate of aggregation of HypF-N under these conditions. This increased rate of aggregation has been shown to be mediated by the interaction of monomers to form initial oligomers, through a particular region in the sequence, corresponding to the sequence part having highly hydrophobicity, the highest beta-sheet propensity and with no net charge at acid pH, representing the ideal segment suitable to mediate protein oligomerization. From all these studies, it is clear that, except the unique native state of globular proteins wherein the side chains pack together in a unique manner, every state of a polypeptide molecule is a broad ensemble of often diverse conformations. It is not surprising, therefore, that even the fibrillar products of aggregation processes are characterized by morphological and structural diversity, representing variations on a common theme. The second part of my PhD Thesis deals with the structural characterization of fibrils. Many studies have been conducted on amyloid aggregates formed under different conditions by peptides, such as A?, TTR and prion fragments (Kodali and Wetzel, 2007). Indeed, the problem of amyloid formation by a full-length protein is more complex, since the dense packing reachable in amyloid fibrils made of peptides (10-40 residues) could not be accomplished in all the amino acid residues of a full-length protein, except in the core regions (Chatani and Goto, 2005). The object of my study was human lysozyme due, most of all, to the fact that some natural variants of human lysozyme (HuL) are responsible for the formation of amyloid plaques in vivo, in a so called familial non-neuropathic systemic amyloidosis (Pepys et al., 1993; Booth et al., 1997). Moreover, it has been possible to exploit the available wealth of structural and folding information about wild type HuL, since it has been shown to be able to form fibrils quite similar to the pathological ones, under acidic conditions and high temperature (Morozova-Roche et al, 2000). With respect to fibrils made of peptides, besides, studying amyloid fibrils conformations from HuL is more challenging because it is a 130 amino acid chain with the structural constrains given by the four disulfide bridges present in the lysozyme molecule. This study can also give some insights into the complex problem of strains diversity, such as for prion diseases, helping the clarification of the structural principles of amyloid fibrils which can produce multiple and distinct amyloid conformations from one protein sequence. In the presented study, fibrils of wild-type HuL formed at low pH have been analyzed by limited proteolysis experiments and Fourier-transform infrared (FTIR) spectroscopy, in order to map conformational features of the 130 residue chain of lysozyme when embedded in the amyloid aggregates (Frare et al., 2006). After digestion with pepsin at low pH, the lysozyme fibrils were found to be composed primarily of N and C-terminally truncated protein species encompassing residues 26-123 and 32-108, although a minority of molecules was found to be completely resistant to proteolysis under these conditions. FTIR spectra provide evidence that lysozyme fibrils contain extensive ?-sheet structure and substantial elements of non ?-sheet or random structure that are reduced significantly in the fibrils after digestion. The sequence 32-108 includes the ?-sheet and helix C of the native protein, previously found to be prone to unfold locally in human lysozyme and its pathogenic variants. Moreover, this core structure of the lysozyme fibrils encompasses the highly aggregation-prone region of the sequence recently identified in hen lysozyme (Frare et al., 2004). The present data indicate that the region of the lysozyme molecule that unfolds and aggregates most readily corresponds to the most highly protease-resistant and thus highly structured region of the majority of mature amyloid fibrils. Overall, the data show that amyloid formation does not require the participation of the entire lysozyme chain. HuL variants, however, aggregate in a physiological environment, roughly at pH 7-7.5 at 37 °C, because of their instability (Dumoulin et al., 2005). In my work, it has been demonstrated that also HuL is able to aggregate under conditions similar to the pathological ones, presumably neutral pH and 37 °C. Considering that HuL forms amyloid fibrils in such different conditions (pH 2.0 50°C and pH 7.5, 60°C), a comparison of the structure and the stability of fibrils obtained under these different conditions has been conducted. In this study HuL fibrils were produced at acidic and at neutral pH, leading both to the formation of fibrils having the three hallmarks of amyloid, that are cross-beta structure, binding of ThT and an overall amyloid fiber morphology. These fibrils have been studied by means of ANS binding, FTIR and X-ray fiber diffraction in order to characterize the differences in the structure. Guanidinium-induced fibrils dissociation, instead, has been applied in order to test the chemical stability of the two kinds of fibrils. The results clearly indicate that the solution conditions used for lysozyme aggregation promote the formation of fibrils with different structural features and stability properties, due to the diverse rearrangements of the lysozyme polypeptide chain into the fibril structure. In conclusion, the research work conducted in this Thesis allowed the comprehension of important aspects of the unfolding of some globular proteins leading to amyloid fibrils. In addition, original data have been obtained on the structural polymorphism of amyloid fibrils.

The aim of this thesis is to investigate and better understand the mechanisms of protein self-assembly. Specifically, I study three protein systems which form morphologically and structurally distinct brillar protein aggregates. The first of these studies is concerned with the self-assembly of amyloid brils formed from bovine insulin. Amyloid brils are associated with human diseases such as Alzheimers Disease and type-2 diabetes, and are also garnering interest in biomaterial applications. Fragmentation-dominated models for the self-assembly of amyloid brils have had important successes in explaining the kinetics of amyloid bril formation but predict bril length distributions that do not match experimental observations. Here I resolve this inconsistency using a combination of experimental kinetic measurements and computer simulations. I provide evidence for a structural transition demarcated by a critical bril mass concentration, or CFC, above which fragmentation of the brils is suppressed. Our simulations predict the formation of distinct bril length distributions above and below the CFC, which I confirm by electron microscopy. These results point to a new picture of amyloid bril growth in which structural transitions that occur during self-assembly have strong effects on the final population of aggregate species with small, and potentially cytotoxic, oligomers dominating for long periods of time at protein concentrations below the CFC. I further show that the CFC can be modulated by environmental conditions, pointing to possible in vivo strategies for controlling cytotoxicity. I probe the structural nature of the transition by performing small angle neutron scattering. Secondly, I study the formation of amyloid-like brils from the protein ovalbumin. I undertake kinetic experiments of self-assembly and find two key features emerge: the lack of a lag time and the existence of a slow growth regime in the long-time limit. I observe, using TEM, that these brils are worm-like in nature and form closed-loops. I find the growth kinetics are intimately connected to this particular morphology. I present a simple kinetic model which captures the features of the kinetics found in experiments by incorporating end-to-end association of brils. I comment on the ramifications this type of amyloid bril assembly may have on oligomeric toxicity. Thirdly, the DNA-mimic protein ocr is highly charged (-56e at pH 8) and forms non-amyloid brillar assemblies at very high ammonium sulphate concentrations (3.2M). The fact that ocr forms translucent brillar gels at such high salt concentrations is extremely unique. Typically under such high salt conditions, non-specific amorphous aggregates are formed. In order to better understand the mechanism of why ocr forms specific bril aggregates, I used variants of the wile-type protein in which extensive regions of surface have been removed or modified. The structural characteristics of gels formed from the variants were probed using microrheological techniques. I find that non-specific electrostatic charge screening plays an important role in ocr aggregation. However, I also locate a potentially important α-helical region which may play a part in establishing specific interactions so that ocr may form ordered brillar assemblies.

Thesis (M.S.)--George Mason University, 2008.
Vita: p. 48. Thesis director: Dmitri Klimov. Submitted in partial fulfillment of the requirements for the degree of Master of Science in Bioinformatics and Computational Biology. Title from PDF t.p. (viewed Mar. 17, 2009). Includes bibliographical references (p. 45-47). Also issued in print.

La Résonance Magnétique Nucléaire (RMN) à l’état solide avec rotation à l’angle magique (MAS) est une technique de choix pour l’étude de la structure et de la dynamique de molécules biologiques peu ou non solubles. Un grand nombre d’approches ont été développées pour la reconstitution de structures tridimensionelles à partir de mesures précises de proximités internucléaires, ainsi que pour la détection de mouvements moléculaires avec une résolution atomique sur des échelles de temps couvrant plusieurs ordres de grandeur. Malgré d’impressionnants progrès, les études par RMN MAS sont cependant loin d’être réalisées en routine. Les déterminations structurelles et de dynamique sont souvent démontrées sur des préparations microcristallines modèles, mais sont encore rares pour des systèmes plus complexes tels que les fibrilles amyloïdes non cristallines ou les protéines trans-membranaires insérées dans des bi- couches lipidiques. Mon travail a pour objectif d’étendre les possibilités de la RMN MAS pour l’étude de systèmes biomoléculaires complexes dans différents états d’agrégation. Pour cela, j’ai exploité les possibilités uniques offertes par les hauts champs magnétiques (fréquence de Larmor du 1H 700, 800 et 1000 MHz) combinés avec les sondes MAS de dernières générations capables d’atteindre des vitesses de rotations supérieures à 60 kHz. Ces conditions expérimentales per- mettent d’augmenter la sensibilité de la RMN MAS à l’aide de la détection 1H à haute résolution et d’enrichir la palette de paramètres RMN rapporteurs de la dynamique des protéines. La première partie de cette thèse décrit le développement de nouvelles stratégies pour l’attribution des résonances du squelette de protéines, pour l’élucidation de structures, et pour l’étude de la dynamique du squelette peptidique et des chaînes latérales. Les méthodes présentées réduisent significative- ment les besoins en termes de temps expérimental, de quantités d’échantillon et de marquage isotopique, et permettent d’analyser par RMN des systèmes de plus hauts poids moléculaire. La seconde partie décrit l’application de la RMN MAS avec détection en 1H pour l’évaluation du rôle de la dynamique des protéines dans des processus tels que la formation de fibrilles amyloïdes et le fonctionnement de protéines membranaires. Une première application est l’étude de la tendance de la β-2 microglobuline humaine à former des fibrilles amyloïdes. Une comparaison de la dynamique du squelette peptidique de la protéine sauvage et du mutant D76N dans leur forme cristalline, ainsi que la détermination de propriétés structurales de la forme fibrillaire m’ont permis d’identifier la présence de repliements pathologiques et de formuler des hypothèses sur le mécanisme de formation des fibrilles. Finalement, la dynamique locale et globale de protéines membranaires dans des bicouches lipidiques a été étudiée. En particulier, le mécanisme d’action d’un transporteur d’alkanes, AlkL, de P. putida a été examiné dans un environnement lipidique. La détermination de paramètres pour la dynamique rapide (ps-ns) et lente (μs-ms) du squelette peptidique de la protéine en présence ou en absence de substrat met en évidence des acheminements possibles pour le transfert de molécules vers la membrane et jette les bases pour une meilleure compréhension du processus
Solid-state NMR with magic angle spinning (MAS) has emerged as a powerful technique for investigating structure and dynamics of insoluble or poorly soluble biomolecules. A number of approaches has been designed for reconstructing molecular structures from the accurate measurement of internuclear proximities, and for probing motions at atomic resolution over timescales spanning several orders of magnitude. Despite this impressive progress, however, MAS NMR studies are still far from routine. Complete determinations, which are often demonstrated on model microcrystalline preparations, are still rare when it comes to more complex systems such as non-crystalline amyloid fibrils or transmembrane proteins in lipid bilayers. My work aimed at extending the possibilities of MAS NMR for applications on complex biomolecular systems in different aggregation states. For this, I exploited the unique possibilities provided by high magnetic fields (700, 800 and 1000 MHz 1H Larmor frequency) in combination with the newest MAS probes capable of spinning rates exceeding 60 kHz. These experimental conditions al- low to boost the sensitivity of MAS NMR through 1H detection at high resolution and to enrich the palette of probes for protein dynamics. The first part of the thesis reports on my contribution to the development of new strategies for backbone resonance assignment, for structure elucidation, and for investigation of backbone and side-chain dynamics. These methodologies significantly reduce the requirements in terms of experimental time, sample quantities and isotopic labeling, and enlarge the molecular size of systems amenable to NMR analysis. The second part describes the application of 1H detected MAS NMR to evaluate the role of protein dynamics in problems such as amyloid fibril formation and membrane protein function. I first addressed the amyloid fibril formation propensity of human beta-2 microglobulin, the light chain of the major histocompatibility complex I. I performed comparative studies of backbone dynamics of the wild type protein as well as a D76N mutant in crystals, and determined some of the structural features of the fibrillar form. This allowed to identify the presence of pathological folding intermediates and to formulate hypotheses on the mechanism of fibrils formation. Finally, I studied the local and global dynamics of membrane proteins in lipid bilayers. In particular, I investigated the mechanism of action of the alkane trans- porter AlkL from P. putida in lipid bilayers. The measurement of parameters for fast (ps-ns) and slow (μs-ms) backbone dynamics of the protein in presence or in absence of a substrate highlights possible routes for molecular uptake and lays the basis for a more detailed mechanistic understanding of the process

Structural analysis of proteins and their complexes is crucial to understanding protein function. This thesis demonstrates the application of mass spectrometry (MS) to the study of pilus assembly on Gram-negative bacteria and amyloid formation in dialysisrelated amyloidosis. In addition, it also tackles the challenging area of membrane protein analysis by MS. Pili are hair-like appendages located on the outer membrane of bacteria that are involved in the transmission of infection. A periplasmic chaperone and an outer membrane usher protein coordinate pilin subunit assembly. Electrospray ionisation (ESI)-MS was used to elucidate the mechanism of subunit assembly. Experiments revealed the specific amino acids on the N-terminal extension of the pilus subunits that are important in catalysing the subunit assembly process. Further MS/MS analysis indicated differences in the stability of the chaperone-subunit-usher ternary complexes formed, providing new insights into the role of the usher in orchestrating pilus biogenesis. Ion mobility spectrometry (IMS)-MS was next used to characterise oligomeric intermediates formed during beta-2 microglobulin (β2m) assembly into amyloid fibrils. Analysis of the oligomers formed by a range of β2m point mutants that affect the kinetics of amyloid fibril formation highlighted the complexity of this fibril-forming process. Further detailed characterisation of the β2m mutant H51A revealed subtle differences in the subunit exchange dynamics of the oligomers involved in fibril formation. Finally, this thesis shows a novel method for solubilising membrane proteins for MS analysis. Amphipathic polymers, termed amphipols, were used to fold and enhance the stability of two bacterial outer membrane proteins, OmpT and PagP. The utility of amphipols to study the structural and functional properties of membrane proteins by ESI-IMS-MS was then developed. Together these data show the power of ESI-IMS-MS in separating conformationally-distinct populations of amphipathic polymers from the amphipol-membrane complex whilst maintaining a ‘native-like’ membrane protein structure in the gas phase.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2011.
Vita. Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references.
Amyloid fibrils are insoluble, non-crystalline protein filaments associated with a number of diseases such as Alzheimer's and Type Il diabetes. They can have a functional role in different organisms and many proteins and peptides have been found to form amyloid fibrils in vitro. We have used magic angle spinning (MAS) NMR spectroscopy to investigate the structure of two amyloid fibril systems - an 11- residue segment from the disease-related protein transthyretin (TTR); and P2- microglobulin (32m), a 99-residue protein associated with dialysis-related amyloidosis. The TTR(105-115) case exemplifies our efforts to characterize the hierarchy of structures present in the fibril form, including the organization of the Pstrands into P-sheets (tertiary structure), the P-sheet interface that defines each protofilament (quaternary structure), and the protofilament-to-protofilament contacts that lead to the formation of the complete fibril. Our efforts were guided by information obtained from other methods such as cryo-electron microscopy and atomic force microscopy, and resulted in the very first atomic resolution structure of a complete amyloid fibril. We have extended the methods used in the TTR(105-115) structure determination procedure to the fibrils formed by 2m, a process complicated not only by the much larger size of the protein involved but also by the high degree of dynamics exhibited in these fibrils. Nevertheless, we were able to characterize the secondary structure of the protein in the fibril form, and the tertiary and quaternary interactions within the fibrils. In addition, we have compared at the molecular level @2m fibrils formed under different conditions, in an effort to characterize the origins of fibril polymorphism for this protein sequence. Our work on amyloid fibrils has also benefited extensively from the development of dynamic nuclear polarization, a method used to enhance the sensitivity of MAS NMR experiments, leading to unprecedented gains in signal-to-noise ratios and acquisition times.
by Galia Tzvetanova Debelouchina.
Ph.D.

In the face of global warming and shrinking resources of fossil fuels the interest in solar energy has increased in recent years. However, the low energy and cost efficiency of current solar cells has up to this date hindered solar energy from playing a major role on the energy market. Photon upconversion is the process in which light of low energy is converted to high energy photons. Lately, this phenomenon has attracted renewed interest and ongoing research in this field mainly focuses on solar energy applications, solar cells in particular. The aim of this study was to investigate and evaluate amyloid fibrils as nanotemplates for an upconversion system based on the dyes platinum octaetylporphyrin (PtOEP) and 9,10- diphenylanthracene (DPA). This well-known pair of organic dyes upconverts light in the visible spectrum through a mechanism known as sensitized triplet-triplet annihilation. Amyloid fibrils are β-sheet rich protein fibril structures, formed by self-assembly of peptides. Amyloid fibrils were prepared from whey protein isolate using heat and acidic solutions. Dyes were incorporated according to a wellestablished technique, in which dyes are grinded together with the protein in solid state prior to fibrillization. Photophysical properties of pure fibrils and dye-incorporated fibrils were studied using UV-VIS spectroscopy and fluorescence spectroscopy. Atomic force microscopy was further employed to confirm the presence of amyloid fibrils as well as to study fibril structure. Results indicate that amyloid fibrils may not be the optimal host material for the upconversion system PtOEP/DPA. It was found that the absorption and emission spectra of this system overlap to a great deal with that of the fibrils. Though no upconverted emission clearly generated by the dye system was recorded, anti-Stokes emission was indeed observed. Interestingly, this emission appears to be strongly enhanced by the presence of dyes. It is suggested that this emission may be attributed to the protein residues rather than the amyloid structure. Future studies are encouraged to further investigate these remarkable findings.
Intresset för solceller har ökat under de senaste åren, till stor del tillföljd av den globala uppvärmningen och de sinande oljeresurserna. Dagens solceller har dock problem med låg energi- och kostnadseffektivitet, vilket gör att solenergin än så länge har svårt att hävda sig på energimarknaden. Photon upconversion är ett fotofysikaliskt fenomen där fotoner med låg energi omvandlas till fotoner med hög energi. Den senaste tiden har denna process fått förnyat intresse och forskningen inom området har ökat, inte minst med sikte på att integrera processen i solceller och därmed öka dess effektivitet. Målet med denna studie var att undersöka huruvida amyloidfibriller kan användas som stomme för ett photon upconversion-system baserat på platinum-oktaetylporfyrin (PtOEP) och 9,10-difenylantracen (DPA). Dessa två organiska färgämnen är ett välkänt par som konverterar synligt ljus med låg frekvens till mer hög frekvent ljus i det synliga spektrumet, via en mekanism som kallas sensitized triplet-triplet annihilation. Amyloidfibriller är proteinbaserade fiberstrukturer med hög andel β-flak, vilka bildas genom självassociation av peptider. I denna studie skapades amyloidfibriller av vassleprotein genom upphettning i sur lösning. Färgämnena inkorporerades enligt en välbeprövad metod där proteinet mortlas tillsammans med färgämnena i fast tillstånd, innan fibrilleringsprocessen påbörjas. De fotofysikaliska egenskaperna hos fibriller med och utan färgämnen analyserade med UV-VIS samt fluorescensspektroskopi. Atomkraftsmikroskopi användes för att bekräfta att fibriller fanns i proven, samt för att studera dess struktur. De erhållna resultaten antyder att amyloidfibriller inte är ett optimalt material för systemet PtOEP/DPA, delvis på grund av att absorptions- och emissionsspektrumet för systemet överlappar med fibrillernas egna spektrum. Anti-Stokes emission detekterades, men denna är med stor sannolikhet inte orsakad av färgämnena. Dock noterades, intressant nog, att denna emission ökar betydligt i närvaro av färgämnena. En möjlighet är att denna emission är kopplad till monomerer i proteinet snarare än till fibrillstrukturen, eftersom emission observerades hos både nativt och fibrillerat protein. Framtida studier uppmuntras att vidare undersöka dessa effekter.

Les maladies dites ''conformationnelles'' sont caractérisées par un mauvais repliement des protéines qui, de ce fait, ne peuvent plus assurer leur fonction biologique. C'est le cas des amyloses, ces pathologies impliquent des protéines ayant la capacité de s'agréger pour former des structures spécifiques appelées « fibres amyloïdes ». Aujourd'hui, une trentaine de protéines humaines sont connues pour former ce type de fibres et notamment la protéine tau. Celle-ci est associée à plusieurs maladies neurodégénératives, regroupées sous le terme de « tauopathies », incluant la maladie d'Alzheimer. En conditions physiologiques, tau est associée aux microtubules et régule leur polymérisation. Dans les tauopathies, elle devient hyperphosphorylée et s'agrège dans les neurones sous forme de neurodégénérescences fibrillaires (NFTs) toxiques. Les protéines chaperons et particulièrement la protéine de choc thermique de 90 kDa, Hsp90, régule l'homéostasie de la protéine tau. L'interaction entre tau et Hsp90 implique différentes régions de la protéine tau dont celle contenant un hexapeptide de séquence VQIVYK. Ce court fragment est nécessaire et suffisant pour induire la fibrillation de la protéine tau entière in vivo. Cet hexapeptide est également capable, à lui seul, de former des fibres amyloïdes, in vitro, comparables à celles retrouvées in vivo. Nous avons donc choisi d'utiliser l'hexapeptide VQIVYK comme modèle d'étude de la fibrillation, in vitro, et testé l'effet de Hsp90 sur les processus agrégatifs du peptide. Nous avons démontré que Hsp90 interagit spécifiquement avec les structures amyloïdes formées par le peptide et qu'elle est capable d'inhiber à la fois la polymérisation et la dépolymérisation des fibres. Ce rôle antagoniste joué par Hsp90 permet la stabilisation d'espèces amyloïdes intermédiaires supposées moins neurotoxiques. Ces résultats confirment l'implication de Hsp90 dans les processus agrégatifs de la protéine tau et ouvrent de nouvelles perspectives thérapeutiques contre les pathologies neurodégénératives. De plus, cette étude apporte des éléments de réponse sur le fonctionnement des chaperons moléculaires vis-à-vis de leur protéine cliente
Conformational diseases are characterized by protein misfolding which causes a loss of biological activity. Amyloidosis is one of these diseases, and it involves the ability of proteins to self-aggregate into specific structures called “amyloid fibers”. At least thirty human proteins, including tau, are known to form amyloid fibers. The tau protein is linked to several neurodegenerative diseases called tauopathies, including Alzheimer’s disease. Tau is in physiological conditions associated with microtubules and regulates their polymerization. In tauopathies, tau becomes hyper-phosphorylated and aggregates into neurotoxic neurofibrillary tangles (NFTs). Molecular chaperones, and particularly the 90-kDa heat shock protein (Hsp90), regulate tau homeostasis. The interaction between tau and Hsp90 involves several tau regions including the sequence VQIVYK. This short fragment is necessary and sufficient on its own to induce aggregation of the full tau protein in vivo. In vitro this hexapeptide is also able to form amyloid fibers similar to those found in vivo. We therefore used this hexapeptide as an in vitro model to study the process of amyloid fibrillation and to test Hsp90’s effects on it. We demonstrated that Hsp90 interacts specifically with peptide fibrillar structures and that Hsp90 is able to inhibit both the polymerization and depolymerization processes. This antagonistic role for Hsp90 allows the stabilization of intermediate amyloid species that may display a lower neurotoxicity. These results confirm that Hsp90 is involved in tau’s aggregation process and paves the way for new therapeutic perspectives in neurodegenerative diseases. Our study also provides clues to the understanding of how molecular chaperones assist in the folding of their client proteins

In this thesis we present computer modelling studies that were implemented to investigate protein behavior in various environments causing their folding, unfolding and aggregation. Applications related to two important proteins - insulin and apolipoprotein C-II (ApoC-II) are presented. The use of atomistic simulation methodologies based on empirical force fields has enhanced our understanding of many physical processes governing protein structure and dynamics. However, the force fields used in classical modelling studies are often designed for a particular class of proteins and rely on continuous improvement and validation by comparison of simulations with experimental data. In Chapter 4 we present a comprehensive comparison of five popular force fields for simulation of insulin. The effect of each force field on the conformational evolution and structural properties of the protein is analysed in detail and compared with available experimental data. A fundamental phenomenon in nature is the ability of proteins to fold ab initio to their functional native conformation, also known as their biologically active state. Due to the heterogeneity and dimensionality of the systems involved, it is necessary to employ methodologies capable of accelerating rare events, specifically, configurational changes that involve the crossing of large free energy barriers. In Chapter 5, using the recently developed method BE-META we were able to identify the structural transitions and possible folding pathways of insulin. Another interesting phenomenon is the misfolding of proteins causing their aggregation, that may lead to formation of either amorphous compounds or structures of elongated-unbranched morphology known as amyloid fibrils. The deposition of amyloid fibrils in the human body may cause many debilitating diseases such as Alzheimer's and variant Creutzfeldt-Jakob diseases, thus making this field of research important and urgent. The human plasma protein apoC-II serves important roles in lipid transport, and it has been shown to form amyloid-like aggregates in solution. We have performed computational studies to investigate the effect of mutations, such as Met oxidation and the residue substitutions to hydrophobic Val and hydrophilic Gln, on dynamics of apoC-II(60-70) peptide. The conformation features relevant to the amyloidogenic propensities of the peptide were identified and presented in Chapter 6. The involvement of lipids at the various stages of development of amyloid diseases is becoming more evident in recent research efforts. In particular, micellar and sub-micellar concentrations have showed to have different effect on fibril growth and kinetics of native apoC-II and derived peptides. In Chapter 7 we investigated the influences of phospholipids at various concentrations on the structure of apoC-II(60-70) using MD and umbrella sampling methods. The molecular mechanisms of lipid effects on the peptide conformation and dynamics were identified. In Chapter 8 preliminary results on the structural stability of pre-formed oligomeric composites of apoC-II(60-70) peptide of different sizes and arrangements were also presented. The effects of mutation (oxidised Met, Met60Val and Met60Gln) on the most stable cluster was also investigated. To conclude, several ideas for continuation of research in the protein folding and aggregation field are discussed in the Future Work section of this thesis.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2003.
Vita.
Includes bibliographical references.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Several methodological developments and applications of multidimensional solid-state nuclear magnetic resonance to biomolecular structure determination are presented. Studies are performed in uniformly 3C, 15N isotope labeled samples with magic-angle spinning for optimal resolution and sensitivity. Frequency selective rotational-echo double-resonance (FSR) and three-dimensional transferred-echo double-resonance (3D TEDOR) methods for carbon-nitrogen distance measurements in (U-'3C,S5N)-labeled peptides and proteins are described. FSR employs frequency selective Gaussian pulses in combination with broadband REDOR recoupling to measure dipolar couplings based on the isotropic chemical shifts of the selected 13C-15N spin pairs. The experiment is demonstrated in model peptides, N-acetyl-L-Val-L-Leu and N-formyl-L-Met-L-Leu-L-Phe, where multiple distances in the 3-6 A range are determined with high precision, and in a membrane protein, bacteriorhodopsin, where the distances between aspartic acids Asp-85 and Asp-212 and the retinal Schiff base nitrogen are measured in the active site. The 3D TEDOR methods employ 13C and 15N chemical shift dimensions for site-specific resolution and encode the distance information in the buildup of cross-peak intensities, allowing multiple distances to be measured simultaneously. The methods are demonstrated in N-acetyl-L-Val-L-Leu and N-formyl-L-Met-L-Leu-L-Phe, where 20 and 26 distances up to 6 A are determined, respectively. The molecular conformation of peptide fragment 105-115 of transthyretin in an amyloid fibril is investigated.
(cont.) Complete sequence-specific 13C and 15N backbone and side- chain resonance assignments are obtained using two-dimensional 13C-13C and 15N-13C-3C chemical shift correlation experiments. Backbone torsion angles are measured directly using three-dimensional dipolar-chemical shift correlation experiments, which report on the relative orientations of 3C-15N, 3C-1H and 15N-'H dipolar tensors, and intramolecular 13C-15N distances in the 3-5 A range are determined using 3D TEDOR, resulting in about 60 constraints on the peptide structure. An atomic-resolution structure of the peptide consistent with the NMR constraints is calculated using simulated annealing molecular dynamics, and the results indicate that the peptide adopts an extended β-strand conformation in the fibril.
by Christopher Peter Jaroniec.
Ph.D.

Les fibres amyloïdes sont souvent à l’origine de nombreuses maladies dégénératives telles que la maladie d’Alzheimer ou la maladie de Parkinson. La formation de ces plaques insolubles est due à une agrégation anormale de protéines. Les études structurales et biologiques des amyloïdes sont hautement complexes du fait de leur organisation sous forme de superstructures unidirectionnelles composées d’une infinité d’unités peptidiques ou protéiques, mais aussi à cause de leur hétérogénéité conformationnelle et polymorphique. Au cours de ces différents travaux de thèse en collaboration avec différents laboratoires d’analyses structurales, nous avons développé plusieurs outils de synthèse tant pour la formation de différents polymorphes de fibres amyloïdes que pour la formation d’espèces oligomériques de tailles conséquentes qui sont un challenge du point de vue synthétique et méthodologique mais aussi pour leur caractérisation. Ces différentes avancées permettront de mieux comprendre les mécanismes de formation de fibres amyloïdes et de préparer des échantillons homogènes pour les analyses structurales et biologiques. L’étude de modifications chimiques telles que la N-méthylation ou les polypeptides D est également un enjeu important pour l’élucidation des interactions protéine-protéine vis-à-vis des structures amyloïdogéniques et ainsi permettre l’élaboration de nouveaux composés inhibant la formation de plaques amyloïdes
Amyloid fibrils are associated with many human disorders including Alzheimer’s or Parkinson’s diseases. The formation of insoluble plaques is the result of protein misfolding and aggregation due to abnormal conformational isomerization of the involved protein. The structural and biological studies of amyloids are highly complex. In this thesis, we report on the development of different synthetic methodologies for the preparation of distinct amyloid fibril polymorphs as homogeneous samples for structural and biological studies. We also synthesized covalently-tethered oligomers composed of nine copies of an amyloidogenic peptide segment, where we were able to control the self-assembly of the structure by insertion of N-methylated amino-acids and to obtain monomeric oligomers mimicking a cross section of an amyloid fibril. We also report on the chiral recognition of L-peptides and L-proteins towards corresponding D-enantiomers during amyloid formation. Moreover, we studied various N-methylated peptide analogues to suppress amyloid growth. Overall, the results obtained in this thesis pave the way towards rational design of peptide-based inhibitors and diagnostics against amyloid propagation

Orientador: Carlos Henrique Inácio Ramos
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia
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Resumo: Proteínas enoveladas incorretamente, com freqüência levam à formação de agregados fibrilares contendo extensas estruturas em folha-?, comumente denominadas de fibrilas amilóides. A hipótese acerca da capacidade de formar fibrilas amilóides com estruturas idênticas e ricas em estruturas beta, ser uma propriedade genérica de toda proteína, apoia-se no fato de até mesmo proteínas sem conexão com doenças, como a mioglobina, serem capazes de gerar estruturas fibrilares. Embora várias proteínas sejam intrinsecamente desordenadas, muitas são apropriadamente empacotadas, podendo se desenovelar totalmente ou parcialmente de maneira a expor regiões propensas à agregação, que podem converter o polipeptídeo em fibrilas amilóides. De fato, vários estudos sugerem que intermediários parcialmente enovelados estão envolvidos na fibrilogênese. A apomioglobina (apoMb) de baleia do espermacete é uma proteína bem caracterizada, que forma um intermediário durante o desenovelamento do estado nativo ou após a diluição do estado desenovelado em tampão de enovelamento. A mioglobina é uma proteína altamente solúvel, cujas propriedades do estado nativo não sugerem uma predisposição dessa em formar fibrilas amilóides, corroborado pela organização de sua seqüência de resíduos de aminoácidos em hélices-? bem definidas sem elementos de estrutura em folha-?. Contudo, até a mioglobina forma fibrilas amilóides em certas condições, sugerindo que a capacidade de formar fibrilas seja uma característica comum de toda proteína e, portanto, não estando relacionada a uma estrutura primária específica. Neste projeto, visamos mapear as potenciais interações envolvidas na agregação e formação de fibrilas amilóides em apomioglobinas. Para tanto, apresentamos aqui os estudos dos efeitos de 19 mutantes de apoMb na cinética amiloidogênica da mesma. A indução de fibrilas amilóides foi realizada através da incubação das apoMbs em tampão borato de sódio 50 mM, pH 9 e aquecidas a 65°C. O processo de agregação foi acompanhado por medidas da emissão de fluorescência de Tioflavina T (ThT) e espectroscopia de dicroísmo circular (CD). Outras propriedades morfo-fisicoquímicas das amilóides de apoMb foram também estudadas: energia de ativação da formação de fibrilas, organização estrutural, citotoxicidade, efeito de semeadura, desmontagem por uréia. Nossos resultados mostram que alguns mutantes (7 no total) afetaram a cinética de formação das amilóides, e surpreendentemente, esses efeitos correlacionam-se bem com o efeito que a mutação tem sobre a estabilidade do estado nativo, mas não com o efeito sobre a estabilidade do estado intermediário do enovelamento. As estruturas globais (investigadas por difração de raios-X) das fibrilas formadas pelas ampomioglobinas selvagem e mutantes mostram-se indistinguíveis. Experimentos de citotoxicidade, utilizando um modelo de células neuronais N2A (neuroblastoma de camundongo), e semeadura, confirmam que as diferentes formas de agregados das proteínas são capazes de diminuir a viabilidade celular e de acelerar a formação das fibrilas. Generalizando, nossos resultados suportam a hipótese de que, embora o desenovelamento parcial preceda a formação de fibrilas em apomioglobina, a formação do intermediário de enovelamento não parece ser um passo obrigatório no processo e assim, o enovelamento e a formação de agregados/fibrilas são aparentemente distintos para essa proteína.
Abstract: Protein misfolding usually leads to the formation of fibrillar aggregates with extensive ?-sheet structure, commonly termed amyloid fibrils. The hypothesis that the ability to form ordered ?-rich amyloid fibers with identical structures is a generic property of proteins is supported by the fact that even proteins with no connection to disease, such as myoglobin, are able to generate fibrillar structures. Although several proteins are intrinsically disordered, many are properly packed and should unfold totally or partially exposing aggregation-prone regions that can convert the polypeptide into amyloid fibrils. Actually, several studies suggest that partially folded intermediates are involved in fibrillogenesis. Sperm whale apomyoglobin (apoMb) is a well-characterized protein that forms an intermediate after either unfolding from the native state or dilution of the unfolded protein in a folding buffer. Mb is a highly soluble protein whose native state properties do not suggest a predisposition to form amyloid fibrils, corroborated by its amino acid residues sequence organization in well-defined ?-helices with no ?-sheet elements. However, even Mb forms amyloid fibrils under certain conditions, suggesting that the ability to form fibrils is a common feature of all proteins and is not related to a specific primary structure. In this work, we aim to map potential interactions involved in apomioglobin aggregation and fibrils formation. To such aim, we present here the studies of effects on amiloidogenic kinetics of 19 apoMb mutants. The induction of amyloid fibrils was performed by incubating apoMb proteins on 50 mM sodium borate buffer at pH 9 and heat to 65°C. The aggregation process was monitored both by thioflavin T (ThT) emitted fluorescence and circular dichroism (CD) spectroscopy measurements. Other morph-physicochemical properties of apoMb amyloids were also studied: activation energy of fibril formation, structure organization, cytotoxicity, seeding effect, disassembly by urea. Our results show that some mutants (7 in total) affect the amyloid formation kinetics, and surprisingly, these effects are well correlated with the effect that the mutation has on the stability of the native state but not with the effect on the stability of the folding intermediate. The overall structures, probed by X-ray diffraction, of fibers formed by mutants and wild-type apomyoglobin are indistinguishable. Cytotoxicity experiments, using a neuronal cell line model N2A (murine neuroblastoma), and seeding experiments, confirm that different aggregated forms of proteins are capable of decreasing the cell viability and to speed up the formation of fibrils. Generally, our results support the hypothesis that although partially unfolding precedes fibril formation in apomyoglobin, formation of the folding intermediate is not an obligatory step in the process and thus folding and aggregation/fibril formation are apparently distinct in this protein.
Doutorado
Bioquimica
Doutor em Biologia Funcional e Molecular

El propòsit d’aquesta tesis que porta com a títol “Estudi de l’estabilitat de plegament i l’agregació mitjançant l’ús de proteïnes globulars petites” és el de contribuir al coneixement de com les proteïnes globulars adquireixen la seva estructura nativa i funcional o, alternativament, despleguen i agreguen donant lloc a assemblatges tòxics. Les malalties conformacionals inclouen un número important de desordres humans com la malaltia del Parkinson i Alzheimer, les quals estan relacionades amb canvis conformacionals d’espècies solubles no tòxiques a agregats tòxics. A més, la sobrexpressió de proteïnes recombinants normalment promou l’acumulació d’agregats proteics, essent un gran blocatge en diversos processos biotecnològics. D’aquesta manera, el desenvolupament d’estratègies per reduir o evitar aquestes reaccions aberrants s’ha convertit en un problema molt important tant a la indústria biomèdica com biotecnològica. En la present tesis hem utilitzat una bateria de tècniques biofísiques i computacionals per analitzar el plegament, l’estabilitat conformacional i la tendència a agregar de diverses proteïnes globulars. La combinació d’aproximacions experimentals (in vivo i in vitro) i bioinformàtiques ha proveït nous coneixements sobre les propietats intrínseques i estructurals, incloent la presència de ponts disulfurs i d’estructura quaternària, que modulen aquests processos sota condicions fisiològiques. En general, aquests resultats demostren com l’establiment de contactes natius que promouen la formació d’intermediaris de plegament, estructures natives o interfases proteiques amb estabilitat termodinàmica significativa és un procés crucial tant en la conducció del plegament proteic com de l’agregació.
The purpose of the thesis entitled “Using small globular proteins to study folding stability and aggregation” is to contribute to understand how globular proteins fold into their native, functional structures or, alternatively, misfold and aggregate into toxic assemblies. Protein misfolding diseases include an important number of human disorders such as Parkinson’s and Alzheimer’s disease, which are related to conformational changes from soluble non‐toxic to aggregated toxic species. Moreover, the over‐expression of recombinant proteins usually leads to the accumulation of protein aggregates, being a major bottleneck in several biotechnological processes. Hence, the development of strategies to diminish or avoid these aberrant reactions has become an important issue in both biomedical and biotechnological industries. In the present thesis we have used a battery of biophysical and computational techniques to analyze the folding, conformational stability and aggregation propensity of several globular proteins. The combination of experimental (in vivo and in vitro) and bioinformatic approaches has provided insights into the intrinsic and structural properties, including the presence of disulfide bonds and the quaternary structure, that modulate these processes under physiological conditions. Overall, the data illustrates how the establishment of native‐like contacts providing folding intermediates, native structures or protein interfaces with significant thermodynamic stability is a crucial process both to drive protein folding and to compete toxic aggregation.

La spectrométrie de masse est devenue un outil indispensable pour la recherche en protéomique, notamment grâce au développement récent de nouveaux spectromètres de masse comme l’Orbitrap et de nouvelles méthodes de dissociation. La stratégie « bottom-up » (analyse des mélanges de peptides protéolytiques) est la plus utilisée par son efficacement et sa simplicité par rapport à la stratégie top-down (analyse des peptides plus longs ou des protéines intactes), mais cette dernière permet une caractérisation plus complète des isoformes de protéines et des modifications post-traductionnelles.Les méthodes de dissociation utilisant des photons, comme la photodissociation dans le domaine ultra-violet (UVPD) et la dissociation multiphotonique infrarouge (IRMPD), ont reçu une grande attention comme approches alternatives aux méthodes de dissociation par collision. L'absorption du photon UV à haute énergie peut être « diluée » sur l'ensemble du peptide ou de la protéine et provoque une fragmentation étendue du squelette peptidique (liaisons C-C), tandis que les photons IR à faible énergie augmentent progressivement l'énergie interne et dissocient préférentiellement les liaisons amide (C-N) les plus labiles.Cette thèse est centrée sur le développement de méthodes et les applications pour une caractérisation structurale de biomolécules par des méthodes d'activation utilisant des photons. L'intérêt de combiner des photons infrarouges à faible énergie et des photons UV à haute énergie dans un spectromètre de masse Orbitrap, pour la caractérisation de petites protéines, a été évalué. En outre, la dissociation infrarouge multiphotonique a été implémentée dans un piège à ions électrostatique afin d’étendre les méthodes de fragmentation aux macromolécules de très haut poids moléculaires dans le domaine mégadalton. L'une des principales avancées de cette thèse a été d'adapter ces méthodes de spectrométrie de masse aux objets biomoléculaires, allant des petits peptides (dans la gamme de masse de kilodalton) à des fibres de protéines entières (dans la gamme de masse de mégadalton)
The structural characterization of proteins often required them to be fragmented into small units containing only few amino acids. In bottom-up approach, proteins are cleaved into small peptides by enzyme then these peptides are subjected to further fragmentation in a collision cell of a tandem mass spectrometer. However, in top-down approach, proteins can directly be dissociated (without enzyme) into small fragments by collision, electron and photon-driven dissociations. Photon-based activation methods including ultraviolet photodissociation (UVPD) and infrared multiphoton dissociation (IRMPD) have received great attention as an alternative to electron-driven and collision induced dissociation methods. Absorption of the high-energy UV photon is dispersed over the whole peptide or protein and stimulates extensive C?Ca backbone fragmentation while the low-energy IR photons gradually increases the internal energy and thus favorably dissociates the most labile amide (C?N) bonds. This thesis focuses on the method development and applications for characterizing biomolecules by photon-based activation methods. The interest of combining high-energy UV photons and low-energy IR photons in an Orbitrap mass spectrometer, for protein and post-translationally modified peptide characterization, has been evaluated. Moreover, infrared multiphoton dissociation has been implemented in a gated electrostatic ion trap to push forward the limit of fragmentation methods to large megadalton ions. One of the main breakthroughs in this thesis is the ability to adapt these method developments and applications to biomolecular objects ranging from small peptides (in kilodalton mass range) to entire protein fibrils (in megadalton mass range)

The topic of this PhD project concerns aspects of the general problem of the protein folding and unfolding, in line with the research conducted in the laboratory of Protein Chemistry at CRIBI, where the activities were mostly performed. The mechanism of acquisition of the three-dimensional structure of proteins (folding) is an important biological event. It is generally a multi-stage process involving the formation of intermediates, which are partly folded states having some structural features of the native protein, but not the final side chains interactions that allow the protein to exert its specific function. The failure in achieving the correct folding (misfolding) may cause protein aggregation. In fact, partly folded proteins can easily self-assembly in regular insoluble aggregates (amyloid fibrils), which are associated with serious diseases, the so called amyloidosis (Chiti & Dobson, 2006). In particular, my PhD research was focused on ?-lactalbumin (?-LA), a milk metalloprotein, widely used as a model to study protein folding. A new wave of interest in this protein appeared in the last decade after the discovery of a variant of the protein that, besides its physiological role in lactation, is able to induce apoptosis of tumor cells (Svensson et al., 1999). The cytotoxic activity resides in the formation of a complex with a milk fatty acid, oleic acid (OA), named HAMLET (Human Alpha-lactalbumin Made LEthal to Tumour cells) (Svensson et al., 2000). The cell events caused by HAMLET were extensively studied (Kohler et al., 2001; Duringer et al., 2003). On the contrary, the mechanism and the nature of the interaction between ?-LA and OA and the physico-chemical properties of the complex are not completely understood yet. The preparation of the complex is a controversial aspect. Indeed, despite the effective association of OA with the protein in solution (Polverino de Laureto et al., 2002), the resulting ?-LA/OA complex was believed to possess lower antitumor activity than HAMLET, obtained using a chromatographic procedure (Svensson et al., 2000). Other debated matters focus on the protein/fatty acid stoichiometry and the monomeric/oligomeric state of ?-LA in the complex. Moreover, a systematic investigation of the effect of the protein on the phase behavior of OA is still lacking. The aim of this PhD Thesis was the investigation of the OA binding propensity and cytotoxic activity of three proteolytic derivatives of bovine ?-LA, obtained by limited proteolysis with pepsin at acidic pH. The use of proteolytic dissection of a protein has been widely employed to study the folding of several proteins (Wetlaufer, 1981; Gegg et al., 1997; Llinás & Marqusee, 1998). The characterization of protein fragments containing specific structural elements of the intact protein (?-helix, ?-sheet) and able of autonomous folding was successfully used to unravel folding features of ?-LA (Polverino de Laureto et al., 1999; 2001). Indeed, fragments corresponding to structural domains in multidomain proteins were shown in some cases to acquire in solution a native-like conformation (Fontana et al., 2004). The ?-LA fragments investigated are: species 1–40/53–123, lacking the ?-subdomain of the native protein; 1–40/104–123, given by the N-terminal fragment 1–40 covalently linked by two disulfide bridges to the C-terminal fragment 104–123 and containing three of the four ?-LA helices; 53–103, containing the C-helix and the calcium binding loop of intact ?-LA (Polverino de Laureto et al., 1999; 2001). The conformational differences between the three fragments were used as the rationale for a study of their efficacy to bind OA, thus giving an insight into the mechanism of this binding. This study has also some physiological relevance: pepsin is an enzyme of the stomach and therefore these species might be generated in vivo, under the same conditions of low pH in which the complex HAMLET was hypothesized to form, thus contributing to the apoptotic activity of the complex formed by the intact protein. The complexes between the three fragments and OA were prepared first by the chromatographic procedure described for HAMLET, then by directly mixing in solution the two components. The conformational properties of the complexes were characterized by circular dichroism, showing that the complexes prepared by both procedures display similar conformations and acquire ?-helix. The effect of calcium on the conformation of the complexes was then investigated by circular dichroism. Fluorescence spectroscopy was used to study the involvement of Trp residues in the interaction with OA. Moreover, the ability of the complexes to induce apoptosis-like cell death was evaluated, in line with the cytotoxic activity displayed by HAMLET. In order to verify the physical state of OA involved in the interaction with ?-LA, the OA aggregation behavior was investigated using different techniques, such as transmission electron microscopy (TEM), titration with a fluorescent dye and turbidimetric analyses, and an effect of solubilization of OA was observed. A manuscript with these results will be soon submitted to an international journal and is herewith attached. In the second part of the PhD, the research was focused on the aggregation propensity of ?-LA and its three proteolytic fragments. ?-LA is able to form amyloid fibrils in vitro, even if not disease-related. ?-LA fibrils are formed when the structure of the protein is partially destabilized, e.g. at low pH, upon reduction of three disulphide bridges at neutral pH (Goers et al., 2002), or after proteolytic cleavage (Polverino de Laureto et al., 2005). Lipids may act as an effective catalyst of fibrillogenesis, providing a generic environment where protein molecules adopt conformation and orientation promoting their assembly into fibrillar structures (Thirumalai et al., 2003; Stefani, 2004; Sparr et al., 2004; Zhao et al., 2004). In particular, since fatty acid–protein interactions are known to modulate the process of fibrillation (Kim & Takahashi 2006), aggregation processes of ?-LA and its fragments were investigated to elucidate whether and how OA might affect fibrils formation. Firstly, aggregation was followed at pH 2.0, as a comparison with the known fibrillogenic behavior of intact ?-LA. Secondly, the aggregation was investigated at pH 7.4, since in this physiological condition the conformational changes induced by OA on the fragments structure were studied and their cytotoxic activity was analyzed, in the first part of the Thesis. The formation of fibrils was followed by thioflavin T (ThT) fluorescence assay, circular dichroism and TEM. All three fragments were able to produce amyloid fibrils at pH 2.0, similarly to ?-LA. In the used range of protein concentration and protein/lipid ratio, OA seems to accelerate the rate of fibrillation for ?-LA and the three fragments at pH 2.0. At pH 7.4, ?-LA is not able to form fibrils both in the absence and in the presence of OA. Also the three fragments did not form amyloid fibrils at neutral pH, while in the presence of OA they underwent a conformational change to ?-sheet structure, were able to bind ThT and to form aggregates with the typical amyloid morphology. During the PhD course, I also collaborated to an ongoing project of the laboratory at CRIBI, focused on the characterization of oligomeric species on the aggregation pathway of human lysozyme, which belongs to the so called “lysozyme/lactalbumin superfamily”. Soluble oligomers of lysozyme were produced at low pH and high temperature, and then analyzed by a range of techniques including binding to fluorescent probes, Fourier-transform infrared (FTIR) spectroscopy and limited proteolysis. Oligomers have solvent-exposed hydrophobic patches, and FTIR spectra are indicative of highly misfolded species. Moreover, the oligomeric lysozyme aggregates were found to be more susceptible to proteolysis than both the monomeric protein and the mature fibrils, indicating their lack of organized structure. This study showed that the soluble lysozyme oligomers are structurally flexible species present at low concentration during the initial phases of aggregation. The results of this study were accepted for publication in an international journal and the ‘in press’ manuscript is attached to the Thesis. During the third year of PhD, I spent a six months period at the University of Cambridge (UK), in the Cambridge Centre for Proteomics, under the supervision of Dr. Kathryn Lilley. The aim of this period was to learn proteomic methodologies for large scale identification of proteins, improving my background in mass spectrometry. I was involved in an ongoing project of the laboratory, focused on a parallel affinity purification method coupled to mass spectrometry for identifying proteins and their binding partners in Drosophila melanogaster embryos (Veraksa et al., 2005). Triple tagged proteins were generated (Spradling et al., 1999) and isolated from a variety of tissues in embryos. Affinity purification using two tags in parallel allowed the isolation of intact native protein complexes. The high sensitivity and high mass accuracy of the hybrid LTQ-Orbitrap instrument ensured maximal coverage of low abundance complex components, generating high confident data with low false discovery rates. The software ProteinCenter™ (Proxeon) was utilized for the visualization and the statistical comparison of the datasets. The data were compared with datasets published in public databases, which validate the data and increased the certainty of the detected interaction sets. Also novel protein interactions not previously reported were mapped. These high confidence in vivo protein datasets add high confidence data to the currently incomplete D. melanogaster proteome and interactome. Here, the results of five different size proteins from different cellular localizations are reported in detail to show the workflow and the efficiency of the methodology. Summing up, this PhD Thesis is composed of a major part dealing with the characterization of the interaction of ?-LA and oleic acid and the effects on the protein aggregation, and a minor part dealing with the mass spectrometry analysis of Drosophila protein complexes, besides the publication on the oligomeric species in the aggregation pathway of lysozyme.
L’argomento di questa Tesi di Dottorato riguarda in generale aspetti del problema del folding e unfolding proteico, in linea con la tematica di ricerca condotta nel laboratorio di Chimica delle Proteine al CRIBI, dove le attività sono state per la maggior parte svolte. Il meccanismo di acquisizione della struttura tridimensionale di una proteina (folding) è un evento biologico importante. In generale, è un processo multi-stadio che coinvolge la formazione di intermedi, che sono stati parzialmente strutturati contenenti alcune caratteristiche strutturali della proteina nativa, ma non le interazioni finali tra le catene laterali che permettono alla proteina di esercitare la sua funzione specifica. Il fallimento nell’acquisizione del corretto folding (misfolding) può causare aggregazione proteica. Infatti, proteine parzialmente strutturate possono facilmente auto-assemblarsi in aggregati regolari insolubili (fibrille amiloidi), associati a gravi malattie, le cosiddette amiloidosi (Chiti & Dobson, 2006). In particolare, il mio progetto di Dottorato è focalizzato sull’?-lattalbumina (?-LA), una metallo-proteina del latte, ampiamente utilizzata come modello di studio del folding proteico. Nell’ultimo decennio, questa proteina ha suscitato un nuovo interesse per la scoperta di una variante che, oltre al ruolo fisiologico nella lattazione, è in grado di indurre apoptosi nelle cellule tumorali (Svensson et al., 1999). L’attività citotossica risiede nella formazione di un complesso con un acido grasso del latte, l’acido oleico (OA), denominato HAMLET (Human Alpha-lactalbumin Made LEthal to Tumor cells) (Svensson et al., 2000). Gli eventi cellulari causati da HAMLET sono stati estesamente studiati (Kohler et al., 2001; Duringer et al., 2003). Al contrario, il meccanismo e la natura dell’interazione tra ?-LA e OA e le proprietà fisico-chimiche del complesso non sono ancora completamente chiariti. Infatti, nonostante l’effettiva associazione dell’OA con la proteina in soluzione (Polverino de Laureto et al., 2002), si ritiene che il complesso così ottenuto possieda attività antitumorale minore dell’HAMLET, preparato secondo una procedura cromatografica (Svensson et al., 2000). Altre questioni dibattute riguardano la stechiometria proteina/acido grasso e lo stato monomerico/oligomerico dell’?-LA nel complesso. Inoltre, manca un’indagine sistematica dell’effetto della proteina sul comportamento di fase dell’OA. Lo scopo di questa Tesi di Dottorato è lo studio della capacità di legare OA ed esprimere attività citotossica di tre derivati proteolitici di ?-LA bovina, ottenuti per proteolisi limitata con pepsina a pH acido. L’uso di un approccio di proteolytic dissection di una proteina è stato largamente impiegato per studiare il folding di molte proteine (Wetlaufer, 1981; Gegg et al., 1997; Llinás & Marqusee, 1998). La caratterizzazione di frammenti proteici, contenenti elementi strutturali specifici della proteina intera (?-elica, ?-sheet) e in grado di assumere struttura in modo autonomo, è stata usata con successo per chiarire caratteristiche strutturali di ?-LA (Polverino de Laureto et al., 1999; 2001). Infatti, frammenti corrispondenti a domini strutturali in proteine multi-dominio hanno mostrato in alcuni casi la capacità di acquisire in soluzione una conformazione simile a quella nativa (Fontana et al., 2004). I frammenti di ?-LA studiati sono: la specie 1–40/53–123, priva di parte del dominio ? della?proteina nativa; 1–40/104–123, formato dal frammento N-terminale 1-40 legato covalentemente al frammento C-terminale 104-123 mediante due ponti disolfuro e contenente tre delle quattro ?-eliche di ?-LA; 53-103, contenente l’elica C e il sito di legame al calcio (Polverino de Laureto et al., 1999; 2001). Le differenze conformazionali dei tre frammenti sono state utilizzate come razionale per studiare la loro efficacia di legame all’OA, e per approfondire quindi il meccanismo di questo legame. Questo studio ha anche rilevanza fisiologica: la pepsina è un enzima dello stomaco e quindi queste specie potrebbero essere generate in vivo, nelle stesse condizioni di pH acido in cui si è ipotizzata la formazione del complesso HAMLET, contribuendo così all’attività apoptotica del complesso formato dalla proteina intera. I complessi dei tre frammenti con OA sono stati preparati prima seguendo la procedura cromatografica descritta per l’HAMLET, poi per diretto miscelamento in soluzione dei due componenti. Le proprietà conformazionali dei complessi sono state caratterizzate mediante dicroismo circolare, mostrando che i complessi preparati attraverso entrambe le procedure presentano conformazioni simili e acquisizione di ?-elica. Inoltre, è stato valutato l’effetto del calcio sulla conformazione dei complessi mediante dicroismo circolare. La spettroscopia di fluorescenza è stata utilizzata per analizzare il coinvolgimento dei residui di Trp nell’interazione con OA. Inoltre, è stata studiata la capacità dei complessi di indurre morte cellulare per apoptosi, in linea con l’attività citotossica mostrata dall’HAMLET. Per analizzare lo stato fisico dell’OA coinvolto nell’interazione con l’?-LA, il comportamento di aggregazione di OA è stato studiato con diverse tecniche, quali microscopia elettronica a trasmissione (TEM), titolazione con un colorante fluorescente e analisi turbidimetriche, ed è stato osservato un effetto di solubilizzazione dell’OA. Questi risultati hanno permesso di preparare un articolo che sarà presto spedito ad una rivista internazionale e che è allegato alla Tesi. Nella seconda parte del Dottorato, la ricerca è stata focalizzata sulla tendenza di ?-LA e dei suoi tre frammenti proteolitici ad aggregare. ?-LA è in grado di formare fibrille amiloidi in vitro, sebbene non sia associata a patologie. Fibrille di ?-LA si producono quando la struttura della proteina è parzialmente destabilizzata, ad esempio a pH acido, per riduzione di tre ponti disolfuro a pH neutro (Goers et al., 2002), o per taglio proteolitico (Polverino de Laureto et al., 2005). I lipidi possono agire come efficaci catalizzatori della fibrillogenesi, creando un ambiente in cui le molecole proteiche adottano una conformazione e un’orientazione che promuove il loro assemblaggio in strutture fibrillari (Thirumalai et al., 2003; Stefani, 2004; Sparr et al., 2004; Zhao et al., 2004). In particolare, poiché è noto che le interazioni proteina-acido grasso modulano il processo di fibrillogenesi (Kim & Takahashi 2006), i processi di aggregazione di ?-LA e dei suoi frammenti sono stati studiati per capire se e come l’OA possa influenzare la formazione di fibrille. In primo luogo, l’aggregazione è stata seguita a pH 2.0, in parallelo con il già noto comportamento fibrillogenico di ?-LA intera. In secondo luogo, l’aggregazione è stata studiata a pH 7.4, poiché in questa condizione fisiologica nella prima parte della Tesi sono stati studiati i cambiamenti conformazionali indotti dall’OA sulla struttura dei frammenti e la loro attività citotossica. La formazione di fibrille è stata seguita mediante saggi di fluorescenza con la tioflavina T (ThT), dicroismo circolare e TEM. Tutti e tre i frammenti sono in grado di produrre fibrille amiloidi a pH 2.0, analogamente all’?-LA. Ai valori di concentrazione proteica e rapporto proteina/lipide utilizzati, OA sembra accelerare la velocità di formazione di fibrille di ?-LA e dei frammenti a pH 2.0. A pH 7.4, ?-LA non forma fibrille amiloidi sia in assenza sia in presenza di OA. Anche i tre frammenti non sono stati in grado di formare fibrille a pH neutro, mentre in presenza di OA hanno mostrato un cambiamento conformazionale verso una struttura ?-sheet, hanno legato ThT e formato aggregati con la tipica morfologia amiloide. Durante il Dottorato, ho inoltre collaborato ad un progetto in corso nel laboratorio al CRIBI, relativo alla caratterizzazione di specie oligomeriche nel processo di aggregazione del lisozima umano, che appartiene alla cosiddetta “superfamiglia lisozima/lattalbumina”. Oligomeri solubili di lisozima sono stati prodotti a pH acido e alta temperatura, e quindi analizzati con varie tecniche, quali legame a molecole fluorescenti, spettroscopia infrarosso in trasformata di Fourier (FTIR) e proteolisi limitata. Gli oligomeri presentano superfici idrofobiche esposte al solvente, e gli spettri FTIR sono indicativi di specie altamente destrutturate. Inoltre, gli aggregati oligomerici di lisozima si sono rivelati più suscettibili alla proteolisi rispetto sia alla proteina monomerica sia alle fibrille mature, indicando la mancanza di una struttura organizzata. Questo studio ha dimostrato che gli oligomeri solubili di lisozima sono specie strutturalmente flessibili presenti a bassa concentrazione durante le fasi iniziali dell’aggregazione. I risultati di questo studio sono stati accettati per la pubblicazione in una rivista internazionale e il manoscritto in press è allegato alla Tesi. Durante il terzo anno di Dottorato, ho trascorso un periodo di sei mesi all’Università di Cambridge (UK), presso il Cambridge Centre for Proteomics, sotto la supervisione della Dr.ssa Kathryn Lilley. L’obiettivo di questo periodo è stato di apprendere metodologie di proteomica per l’identificazione di proteine su larga scala, ottimizzando le mie conoscenze di spettrometria di massa. Ho collaborato ad un progetto in corso nel laboratorio, incentrato su un metodo di purificazione di affinità in parallelo accoppiata a spettrometria di massa per identificare complessi proteici in embrioni di Drosophila melanogaster (Veraksa et al., 2005). Proteine con tre tags sono state generate (Spradling et al., 1999) e isolate da vari tessuti embrionali. La purificazione di affinità usando due tags in parallelo ha permesso di isolare complessi proteici nativi intatti. L’alta sensibilità e l’alta accuratezza di massa dello strumento ibrido LTQ-Orbitrap ha assicurato la massima copertura di componenti di complessi poco abbondanti, generando dati ad alta confidenza con basse false discovery rates. È stato utilizzato il software ProteinCenter™ (Proxeon) per la visualizzazione e l’analisi statistica dei set di dati. I risultati sono stati confrontati con dati presenti in database pubblici, confermandone la validità e aumentando l’autenticità delle interazioni individuate. Sono state inoltre mappate nuove interazioni proteiche non riportate in precedenza. Questi set di dati in vivo aggiungono alta confidenza al proteoma e ‘interattoma’ di D. melanogaster attualmente incompleto. In questa Tesi sono riportati in dettaglio i risultati di cinque proteine di diverse dimensioni e localizzazione cellulare, per presentare la procedura e l’efficienza della metodologia. In sintesi, questa Tesi di Dottorato è composta da una parte principale che riguarda la caratterizzazione dell’interazione tra ?-LA e acido oleico e gli effetti sull’aggregazione proteica, e una parte minore relativa all’analisi di spettrometria di massa di complessi proteici in Drosophila, oltre alla pubblicazione sulle specie oligomeriche studiate nel processo di aggregazione del lisozima.

The inherited form of primary open angle glaucoma, a disorder characterized by increased intraocular pressure and retina degeneration, is linked to mutations in the olfactomedin (OLF) domain of the myocilin gene. Disease-causing myocilin variants accumulate within trabecular meshwork cells instead of being secreted to the trabecular extracellular matrix thought to regulate aqueous humor flow and control intraocular pressure. Like other diseases of protein misfolding, we hypothesize myocilin toxicity originates from defects in protein biophysical properties. In this thesis, the first preparative recombinant high-yield expression and purification system for the C-terminal OLF domain of myocilin (myoc-OLF) is described. To determine the relative stability of wild-type (WT) and mutant OLF domains, a fluorescence thermal stability assay was adapted to provide the first direct evidence that mutated OLF is folded but less thermally stable than WT. In addition, mutant myocilin can be stabilized by chemical chaperones. Together, this work provides the first quantitative demonstration of compromised stability among identified OLF variants and placing myocilin glaucoma in the context of other complex diseases of protein misfolding. Subsequent investigations into the biophysical properties of WT myoc-OLF provide insight into its structure and function. In particular, myoc-OLF is stable in the presence of glycosaminoglycans (GAGs), as well as over a wide pH range in buffers with functional groups reminiscent of such GAGs. Myoc-OLF contains significant â-sheet and â-turn secondary structure as revealed by circular dichroism analysis. At neutral pH, thermal melts indicate a highly cooperative transition with a melting temperature of ~55°C. A compact core structural domain of OLF was identified by limited proteolysis and consists of approximately residues 238-461, which retains the single disulfide bond and is as stable as the full myoc-OLF construct. This construct also is capable of generating 3D crystals for structure determination. This data, presented in Chapter 3, inform new testable hypotheses for interactions with specific trabecular extracellular matrix components. To gain further insight into the biological function of myoc-OLF, a facile fluorescence chemical stability assay was designed to identify possible ligands and drug candidates. In the assay described in Chapter 4, the target protein is initially destabilized with a chemical denaturant and is tested for re-stabilization upon the addition of small molecules. The assay requires no prior knowledge of the structure and/or function of the target protein, and it is amendable to high-throughput screening. Application of the assay using a library of 1,280 compounds revealed 14 possible ligands and drug candidates for myoc-OLF that may also generate insights into myoc-OLF function. Due to the high â-sheet content of monomeric myoc-OLF and presence of an aggregated species upon myoc-OLF purification, the ability of myoc-OLF to form amyloid fibrils was suspected and verified. The fibril forming region was confirmed to reside in the OLF domain of myocilin. Kinetic analyses of fibril formation reveal a self-propagating process common to amyloid. The presence of an aggregated species was confirmed in cells transfected with WT myocilin, but to a greater extent in cells transfected with P370L mutant myocilin. Both cell lines stained positive for amyloid. Taken together, these results provide further insights into the structure of myocilin and suggest a new hypothesis for glaucoma pathogenesis. Finally, in a related study, small molecule drug candidates were investigated to treat acid â-glucosidase (GCase), the deficient lysosomal enzyme in Gaucher disease, another protein conformational disorder. Three new GCase active-site directed 3,4,5,6-tetrahydroxylazepane inhibitors were synthesized that exhibit half inhibitory concentrations (IC50) in the low millimolar to low micromolar range. Although the compounds thermally stabilize GCase at pH 7.4, only one of the synthesized analogs exhibits chaperoning activity under typical assay conditions. This successful pharmacological chaperone is also one in which GCase is in its proposed active conformation as revealed by X-ray crystallography. Probing the plasticity of the active-site of GCase offers additional insight into possible molecular determinants for an effective small molecule therapy for GD.