Academic literature on the topic 'Sdsl-Epr'

Site-directed spin labeling (SDSL) in combination with electron paramagnetic resonance (EPR) spectroscopy enables studies of the structure, dynamics, and interactions of proteins in the noncrystalline state. The scope and analytical value of SDSL–EPR experiments crucially depends on the employed labeling strategy, with key aspects being labeling chemoselectivity and biocompatibility, as well as stability and spectroscopic properties of the resulting label. The use of genetically encoded noncanonical amino acids (ncAA) is an emerging strategy for SDSL that holds great promise for providing excellent chemoselectivity and potential for experiments in complex biological environments such as living cells. We here give a focused overview of recent advancements in this field and discuss their potentials and challenges for advancing SDSL–EPR studies.

Abstract Site-directed spin labeling (SDSL) in combination with electron paramagnetic resonance (EPR) spectroscopy has emerged as an efficient tool to elucidate the structure and the conformational dynamics of proteins under conditions close to the native state. This review article summarizes the basics as well as the recent progress in SDSL and EPR methods, especially for investigations on protein structure, protein function, and interaction of proteins with other proteins or nucleic acids. Labeling techniques as well as EPR methods are introduced and exemplified with applications to systems that have been studied in the author’s laboratory in the past 15 years, headmost the sensory rhodopsin-transducer complex mediating the photophobic response of the halophilic archaeum Natronomonas pharaonis. Further examples underline the application of SDSL EPR spectroscopy to answer specific questions about the system under investigation, such as the nature and influence of interactions of proteins with other proteins or nucleic acids. Finally, it is discussed how SDSL EPR can be combined with other biophysical techniques to combine the strengths of the different methodologies.

Site-directed spin labeling (SDSL) in combination with electron paramagnetic resonance (EPR) spectroscopy is a rapidly expanding powerful biophysical technique to study the structural and dynamic properties of membrane proteins in a native environment. Membrane proteins are responsible for performing important functions in a wide variety of complicated biological systems that are responsible for the survival of living organisms. In this review, a brief introduction of the most popular SDSL EPR techniques and illustrations of recent applications for studying pertinent structural and dynamic properties on membrane proteins will be discussed.

Site-directed spin labeling (SDSL) combined with continuous wave electron paramagnetic resonance (cw EPR) spectroscopy is a powerful technique to reveal, at the local level, the dynamics of structural transitions in proteins. Here, we consider SDSL-EPR based on the selective grafting of a nitroxide on the protein under study, followed by X-band cw EPR analysis. To extract valuable quantitative information from SDSL-EPR spectra and thus give a reliable interpretation on biological system dynamics, a numerical simulation of the spectra is required. However, regardless of the numerical tool chosen to perform such simulations, the number of parameters is often too high to provide unambiguous results. In this study, we have chosen SimLabel to perform such simulations. SimLabel is a graphical user interface (GUI) of Matlab, using some functions of Easyspin. An exhaustive review of the parameters used in this GUI has enabled to define the adjustable parameters during the simulation fitting and to fix the others prior to the simulation fitting. Among them, some are set once and for all (gy, gz) and others are determined (Az, gx) thanks to a supplementary X-band spectrum recorded on a frozen solution. Finally, we propose guidelines to perform the simulation of X-band cw-EPR spectra of nitroxide labeled proteins at room temperature, with no need of uncommon higher frequency spectrometry and with the minimal number of variable parameters.

Investigations on the structure and function of biomolecules often depend on the availability of topological information to build up structural models or to characterize conformational changes during function. Electron paramagnetic resonance (EPR) spectroscopy in combination with site–directed spin labeling (SDSL) allow to determine intra- and intermolecular distances in the range from 4–70 Å, covering the range of interest for biomolecules. The approach does not require crystalline samples and is well suited also for molecules exhibiting intrinsic flexibility. This article is intended to give an overview on pulsed EPR in conjunction with SDSL to study protein interactions as well as conformational changes, exemplified on the tRNA modifying enzyme MnmE.

Here we introduce chiLife, a Python package for site-directed spin label (SDSL) modeling for electron paramagnetic resonance (EPR) spectroscopy, in particular double electron–electron resonance (DEER). It is based on in silico attachment of rotamer ensemble representations of spin labels to protein structures. chiLife enables the development of custom protein analysis and modeling pipelines using SDSL EPR experimental data. It allows the user to add custom spin labels, scoring functions and spin label modeling methods. chiLife is designed with integration into third-party software in mind, to take advantage of the diverse and rapidly expanding set of molecular modeling tools available with a Python interface. This article describes the main design principles of chiLife and presents a series of examples.

AbstractCellular membranes and associated proteins play critical physiological roles in organisms from all life kingdoms. In many cases, malfunction of biological membranes triggered by changes in the lipid bilayer properties or membrane protein functional abnormalities lead to severe diseases. To understand in detail the processes that govern the life of cells and to control diseases, one of the major tasks in biological sciences is to learn how the membrane proteins function. To do so, a variety of biochemical and biophysical approaches have been used in molecular studies of membrane protein structure and function on the nanoscale. This review focuses on electron paramagnetic resonance with site-directed nitroxide spin-labeling (SDSL EPR), which is a rapidly expanding and powerful technique reporting on the local protein/spin-label dynamics and on large functionally important structural rearrangements. On the other hand, adequate to nanoscale study membrane mimetics have been developed and used in conjunction with SDSL EPR. Primarily, these mimetics include various liposomes, bicelles, and nanodiscs. This review provides a basic description of the EPR methods, continuous-wave and pulse, applied to spin-labeled proteins, and highlights several representative applications of EPR to liposome-, bicelle-, or nanodisc-reconstituted membrane proteins.

Membrane proteins possess a variety of functions essential to the survival of organisms. However, due to their inherent hydrophobic nature, it is extremely difficult to probe the structure and dynamic properties of membrane proteins using traditional biophysical techniques, particularly in their native environments. Electron paramagnetic resonance (EPR) spectroscopy in combination with site-directed spin labeling (SDSL) is a very powerful and rapidly growing biophysical technique to study pertinent structural and dynamic properties of membrane proteins with no size restrictions. In this review, we will briefly discuss the most commonly used EPR techniques and their recent applications for answering structure and conformational dynamics related questions of important membrane protein systems.

L'étude des biomolécules dans leur environnement natif, la cellule, est l'un des principaux objectifs de la biologie structurale au cours de la dernière décennie. Ainsi, nous assistons à un remarquable développement des approches dites « in-cell », comme la CryoET, FRET (Förster Resonance Energy Tranfer), RMN. Parmi elles, la technique de marquage de spin couplée à la spectroscopie de Résonance Paramagnétique Electronique (SDSL-RPE) présente des caractéristiques intéressantes et avantageuses permettant de sonder la dynamique des protéines à l'intérieur des cellules. En particulier, l’utilisation des sondes de type nitroxyde combine sensibilité élevée et absence de contraintes de taille de la biomolécule d'intérêt avec la capacité d'étudier les transitions structurales et les interactions protéines-protéines à température physiologique. Cependant, même si de nombreux efforts ont été faits pour adapter cette technique à des études structurales dans les cellules, des progrès restent à faire.Dans cette thèse, nous traitons des principales limitations de l’utilisation des nitroxydes dans un contexte cellulaire. Nous nous sommes concentrés sur la stabilité des marqueurs nitroxydes dans des milieux reducteurs et dans la cellule, sur l’incorporation des protéines marquées dans les cellules et la viabilité de ces cellules en vue de mesures par RPE. Grâce aux résultats obtenus dans cette partie méthodologique, nous avons pu étudier la dynamique structurale de deux protéines chaperons (NarJ et UreG) dans des cellules bactériennes. Ces avancées ont permis de comparer les données obtenues in-cell à celles obtenues in vitro ou dans un environnement mimant le milieu cellulaire
The study of biomolecules in their native environment has been one of the main goals of structural biology in the last decade. As a result, we are assisting to a remarkable increase of new "in-cell" approaches, like Cryo-ET, FRET and NMR. Among these approaches, Site-Directed Spin Labeling (SDSL) coupled to Electron Paramagnetic Resonance (EPR) spectroscopy shows competitive and advantageous features to capture protein dynamics inside cells. In particular, nitroxide-based SDSL-EPR combines the advantages of high sensitivity and the lack of size constraints on the biomolecule of interest with the ability to capture protein structural transitions and interactions at physiological temperature. Despite the methodological advancements of the technique that have allowed the community to obtain increasingly relevant results, progresses still need to be done.In this work, the main limitation of nitroxide-based SDSL-EPR has been addressed. In the first time, we focused on the development of delivery methods to introduce the labeled protein in bacterial cells. Next, the stability of nitroxide labels in reducing environments and in-cell has been assessed, monitoring in parallel the viability of the cells during the EPR measurements. Thanks to the results achieved in this methodological part, we were able to study the structural dynamics of two flexible chaperone proteins directly in bacterial cells: NarJ from Escherichia coli and UreG from Sporosarcina pasteurii. Finally, to go further in understanding the impact of the cellular environment on the protein dynamics, the data obtained in cellular context were compared with those obtained in vitro or in a cell-mimicking environment

In this work 3 different proteins are subjected to investigations on their structural, dynamic and functional properties by SDSL EPR spectroscopy, combined with in silico structure prediction and modeling: the pore-forming bacterial toxin colicin A in its membrane-bound form and its corresponding immunity protein Cai, and the Na+/proline symporter PutP. Colicin A (ColA) is a plasmid-encoded water-soluble pore-forming toxin produced by certain E. coli strains that kills unprotected cells of related strains by inserting a pore-forming subdomain into the cytoplasmic membrane to form voltage-dependent ion channels. Detailed structural data for the membrane-bound channel, in the closed as well as in the open state, is still missing, thus in the present study, the in vitro investigation by site-directed spin labeling and EPR spectroscopy has been substantially extended. The results indicate that a larger fraction of the protein than previously suggested penetrates into the hydrophobic core of the membrane, and distance measurements by pulse and cw EPR spectroscopy provide evidence that ColA in lipid bilayer membranes forms an oligomeric structure. Pulse EPR distance measurements under in vivo conditions reveal clear indications for an oligomeric ColA structure also in vivo. The results of all EPR measurements were combined to construct a dimer model for the colicin A closed channel state conformation. The immunity protein Cai, an integral inner membrane protein, protects the producing E. coli cell from the cytotoxic activity of its corresponding toxin (colicin A), by preventing channel opening by a yet unknown mechanism. ESR measurements for single spin label probes attached to ColA in the presence and absence of the immunity protein Cai reveal a clear influence on the ColA helices of the pore-forming domain in the presence of Cai as previously postulated. The data suggest that Cai induces a conformational change in/for the voltage sensor helix H6 of ColA, forming a “locked” inactive channel conformation that is not capable of voltage sensing and channel opening. Initial experiments with spin labeled wt-Cai in the presence and absence of unlabeled ColA suggest a more compact structure in the presence of ColA. PutP is an integral membrane protein located in the cytoplasmic membrane of E. coli, being responsible for the coupled transport of Na+ and proline in a 1:1 stoichiometry. It belongs to the family of sodium solute symporters (SSSF). Three dimensional structural data for PutP are at the moment not available, but a homology model has been developed based on the crystal structure of another member of this protein family, the Na+/galactose symporter vSGLT of Vibrio parahaemolyticus. The observed periodicity in spin label mobility and polarity measurements suggest a secondary structure of the extracellular Loop eL4 of PutP of two α-helical segments eL4a and eL4b, and imply the idea of eL4 functioning as an external gate to the SSSF. The ligand-induced changes observed in mobility, polarity and accessibility upon substrate binding support this notion, thus providing further insights into the mechanistic basis of sodium solute symport.

The photosensitive unit triggering the negative phototaxis in the haloarchaeum Natronomonas pharaonis consists of the receptor sensory rhodopsin II (NpSRII) and its cognate transducer (NpHtrII) in a 2:2 stoichiometry. Upon light excitation, a structural rearrangement in the receptor initiates a displacement/rotation of the transducer helix TM2, which can be considered as starting event for the signal transduction. This signal is further transmitted to the cytoplasmic signaling domain through the signal transduction unit comprising two HAMP domains.Structural information already exists for the transmembrane region of this complex (crystal structure) as well as for the rod shaped cytoplasmic part of NpHtrII due to its high homologies with chemoreceptors. Moreover, the solution NMR structure of the isolated HAMP domain from A. fulgidus recently obtained shows a homodimeric, four-helical, parallel coiled-coil with an unusual interhelical packing, that is thought to propagate a signal by virtue of concerted helix rotations. Here, an electron paramagnetic resonance (EPR) investigation of site-directed spin labeled transducers in the NpSRII/NpHtrII complex has been carried out for structural and functional elucidation of the N. pharaonis HAMP. For this purpose, cw as well as pulse EPR techniques have been used in terms of mobility, accessibility and intra-transducer dimer distance analyses. Conformational changes induced by environmental inputs, namely salt, temperature and pH, give insight into the two-state equilibrium existing between a highly dynamic (dHAMP) and a more compact (cHAMP) conformation of this linker region.

Understanding the conformational and dynamic changes of biomacromolecular complexes in different states, such as the membrane protein photoreceptor-transducer complex NpSRII/NpHtrII, is a key step to gaining insight into the functional mechanism of these important classes of protein complexes, since ~30 % of the human proteome are membrane proteins, yet they are largely underrepresented in terms of structural information with <1 % of all structures in the protein data bank. Hence for the development of methods suitable to study the conformation and dynamics of such complexes there is a strong demand and a vast potential field of applications. Here we combined method development at the interface between biomolecular simulations and model-based analysis of EPR- and fluorescence spectroscopic data with application studies using state-of-the-art spectroscopic techniques in conjunction with site-directed spin- or fluorescence labeling. In an initial benchmark study on the rigid globular protein complex Rpo4/7, we compared experimental inter fluorescence label distances or spin label distance distributions to a variety of predicted inter label distances based on molecular dynamics simulations, Monte Carlo sampling and a discrete rotamer library analysis. We found that while for the molecular dynamics simulations with explicit solvent considerable sampling challenges have to be overcome to reproduce the experimentally observed inter label distance distributions, the Monte Carlo sampling performed well when compared to the experimental data and was computationally less demanding. Significantly more efficient and equally accurate for our examples was the so-called rotamer library analysis available for the spin labels since it relies on a pre-calculated set of rotational isomers. In general, predictions for the mean distances were in agreement within the error margins while distribution shapes were more challenging to reproduce. Overall this study shows a positive evaluation for the assessed tools and the developed simulation protocols as well as their potential applications. Using the combination of EPR and fluorescence spectroscopy for distance determination we studied the structural influence of RNA binding on Rpo4/7, and showed that the protein complex stays conformationally rigid and thereby serves as a guiding rail for the nascent RNA chain that leaves the RNA polymerase along the Rpo4/7 RNA binding interface. To enhance the interpretation of experimentally determined changes of conformation and dynamics in protein complexes and to discuss the observed changes in terms of structural information, we built models of the two transcription factors TFE and the Spt4/5 complex, as well as of Argonaute, a 713 amino acid four-domain protein nuclease from Methanocaldococcus jannaschii. These structural models not only allowed a more accurate planning of fluorescence or EPR labeling experiments, but also the models enabled the discussion of the experimental data in structural terms. Based on such an initial structure further computational analysis techniques may be applied to identify putative structural changes or dynamic modes. This was shown for the histidine transporter HisQMP2, where we combined normal mode analysis to model protein flexibility with the rotamer library analysis to screen for possible conformational changes in comparison to experimental inter spin distance data. The most prominent agreement with one mode led to a working hypothesis of a conformational change and provides the basis for validation in future experiments. Due to the inherent synergy effects, we applied a combined experimental and simulation approach for the EPR-based distance determination in the globular DNA-binding protein LexA to probe conformation and dynamics of the N-terminal DNA-binding domains with respect to the C-terminal domains within the LexA homodimer. While the C-terminal dimerization domains exhibit a well-defined conformation that proved to be independent of DNA-binding, large-scale changes in conformation and dynamics were detected for the N-terminal domains. They were only found in a defined conformation when bound to DNA while in its absence a large rotational freedom of the entire N-terminal domains contributed to the conformational ensemble. Combined with a biochemical characterization of the autocatalytic cleavage of LexA, our data explains how LexA induces the SOS response after DNA damage or under latent antibiotic stress. We further studied the membrane photoreceptor-transducer complex NpSRII/NpHtrII that governs the light-dependent swimming behavior in Natronomonas pharaonis by a two-component signaling system. This system comprises extraordinary features of sensitivity, signal amplification, integration and transducer cooperativity, yet the molecular details of these features are poorly understood, as is signal propagation itself. By combining time-resolved cw EPR spectroscopy of NpSRII/NpHtrII variants spin labeled in the HAMP1 domain with time-resolved optical absorbance spectroscopy to report on the receptor signaling state, we found a tight kinetic coupling of receptor and transducer during the relaxation back to the ground state and hence a prolonged activation period, that with ~500 - ~700 ms is sufficiently long to cause phosphorylation bursts of the cognate kinase CheA. This explains signal amplification already on the level of the NpSRII/NpHtrII dimers. We further determined the transient difference spectra from the time-resolved EPR data that show local differences in dynamics and steric restrictions upon light-activation. Comparing these experimentally observed differences to predictions confirms the assumed two-state structural model and shows this transition between the two states for a single HAMP domain in a light-dependent manner. Additionally, our approach integrates a dynamic view into the model, since the two states are shown to exhibit different local dynamics in a fashion described previously as a competing model for signaling by dynamic differences based on biochemical studies. Here we show unification of the two models into one congruent description encompassing a transition between the two previously suggested states by concerted structural and dynamic changes. In an independent analysis using all-atom and coarse grained molecular dynamics of the NpSRII/NpHtrII complex in the minimal unit that can exert kinase control, the trimer of receptor-transducer dimers, we revealed a distinct dynamical pattern encoded in the primary sequence of the coiled-coil heptad-repeats. Upon receptor activation, these segments alter their dynamics in a concerted fashion with regions such as HAMP1 and the adaptation region becoming more compact, while HAMP2 and the tip become more dynamic, leading to dynamic and to limited structural changes at the CheA-kinase binding sites. Together with an extensive validation against experimental data, these findings suggest the altered dynamics as the mechanism for signal propagation along the extended coiled-coil structure of NpHtrII. This working model, that explains the current body of experimental data, allows for further refinement by all-atom molecular dynamics and provides a basis to devise future experiments for validation. The presented studies outline the versatile methodology of combined experimental and simulation approaches to analyze the conformation and dynamics of biomacromolecules including membrane protein complexes.

The fundamental task of de novo protein folding and refolding is ensured by the diverse family of molecular chaperones. Insight into the structure, conformational changes and client interactions is key to understanding the processes within the complex chaperone network. Electron paramagnetic resonance (EPR) spectroscopy combined with site-directed spin labeling (SDSL) is a suitable technique to unravel the processes involving chaperone activity. In this chapter, we review the state-of-the-art SDSL-EPR methodology, in particular distance determination providing structural information. Recent work in the field of molecular chaperones studied by EPR spectroscopy is summarized illustrating the tremendous potential and versatile applicability of this method.