Dissertations / Theses: 'Model lipid membrane'

1

Oldham, Alexis Jean. "Modulation of lipid domain formation in mixed model systems by proteins and peptides." View electronic thesis, 2008. http://dl.uncw.edu/etd/2008-1/r1/oldhama/alexisoldham.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

2

Botelho, Ana Vitoria. "Lipid-protein interactions: Photoreceptor membrane model." Diss., The University of Arizona, 2005. http://hdl.handle.net/10150/280765.

Full text

Abstract:

G-protein coupled receptors (GPCRs) are transmembrane proteins capable of recognizing an astonishing variety of biological signals, ranging from photons of light to hormones, odorants, and neurotransmitters involved in key biological signaling processes. The aim of this work is to identify how lipid-protein interactions involving the membrane bilayer ultimately affect such vital biological functions. Here the relationship between the bilayer thickness, hydrophobic mismatch, and protein aggregation are investigated by expanding the framework of membrane-receptor interactions in terms of a new flexible surface model. Previously, we have shown how coupling of the elastic stress-strain due to mismatch of the spontaneous curvature and hydrophobic thickness at the lipid/protein interface can govern the conformational transitions of membrane proteins. This approach has now been extended to include coupling of the lateral organization of the GPCR rhodopsin to the curvature and area stress and strain of the proteolipid membrane. Rhodopsin was labeled with site-specific fluorophores, and a FRET technique was employed to probe protein association in different lipid environments. Moreover, UV-visible spectroscopy was used for thermodynamic characterization of the conformational change of rhodopsin. Lastly, the deformation of the lipids with and without rhodopsin was probed in terms of acyl chain order parameters and relaxation rates by solid-state NMR methods, giving insight into the lipid deformation. The results showed that optimal receptor activation occurs in phosphatidylcholine bilayers of 20-carbon acyl chain length, hence one can say that metarhodopsin II is likely to adopt an elongated shape. Lipids promoting aggregation, or below their gel to liquid crystalline transition temperature all favor formation of metarhodopsin I. The data also showed that association and activation of rhodopsin do not always correlate. In terms of the extended flexible surface model, the stress due to hydrophobic mismatch is coupled via the effective number of lipids surrounding the protein due to the lateral organization of the membrane. The measured changes in rhodopsin-rhodopsin interactions and membrane influences on the conformation of the protein after photoisomerization may be crucial to understanding physiological regulation of the rod disk membranes. They are relevant to understanding the complexity of biomembranes involved in many cellular mechanisms, including signal transduction.

APA, Harvard, Vancouver, ISO, and other styles

3

Polozov, Ivan V. "Interactions of class A and class L amphipathic helical peptides with model membranes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape16/PQDD_0006/NQ30110.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Bechtella, Leïla. "Molecular analysis of the interactions of the cell-penetrating peptide Penetratin and lipid membranes. Contributions of the lipid PIP2, biophysical approaches and benzophenone photoreactivity in model membranes." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS045.

Full text

Abstract:

Les peptides vecteurs (CPP) peuvent entrer dans les cellules et y transporter des molécules biologiquement actives. De précédents travaux ont montré que les CPP pouvaient remodeler le cytosquelette d'actine, interagissaient fortement avec les lipides chargés négativement et que le PIP2 pourrait jouer un rôle dans l'internalisation de la Pénétratine. Nos expériences en DSC ont montré que la Pénétratine interagit avec les têtes polaires et influence la fluidité de la membrane de vésicules contenant du PIP2. La présence de PIP2 favorise l’interaction Pénétratine-lipide. De plus, l’estimation de l'affinité de liaison par fluorescence du tryptophane a montré que la Pénétratine a une affinité plus élevée pour le PIP2 que pour la PS. Le photomarquage par affinité couplé à la spectrométrie de masse, à l'aide de peptides fonctionnalisés par une benzophénone (Bzp), a permis d’étudier les interactions non covalentes des CPP et des membranes lipidiques à un niveau moléculaire. Le PIP2 s'est avéré être un partenaire d'interaction de la Pénétratine et a été marqué préférentiellement dans les liposomes contenant du PC, de la PS et du PIP2. Nous avons mis en évidence des réactions secondaires très informatives qui peuvent se produire simultanément lors de l'irradiation UV, dans un unique système biologique : un CPP inséré dans une bicouche lipidique. Ce travail montre comment exploiter de manière originale les différentes réactivités de la Bzp dans le contexte d'une membrane lipidique, informant sur l'interaction CPP/lipide au niveau moléculaire comme la profondeur d'insertion ou la fluidité membranaire au voisinage du CPP
Cell-penetrating peptides (CPP) can cross cell membranes and deliver biologically active molecules into cells. Previous work showed that CPPs could remodel the actin cytoskeleton, interacted strongly with negatively charged lipids and PIP2 could play a role in Penetratin internalization. Our DSC experiments showed that Penetratin interacts with polar head groups and impacts the lipid bilayer fluidity of PIP2-containing liposomes. It indicated that presence of PIP2 in liposomes triggers Penetratin-lipid interaction. Moreover, Penetratin binding affinity for PIP2-containing lipid vesicles, estimated by tryptophan fluorescence, pointed out that Penetratin has a higher affinity for PIP2 than for PS. Affinity photocrosslinking coupled to mass spectrometry, using benzophenone (Bzp)-functionalized peptides, was used to study the non-covalent interactions of CPPs and lipid membranes at a molecular level. PIP2 was found to be a good interaction partner for Penetratin and was preferably labelled in liposomes containing PC, PS and PIP2. We revealed highly informative secondary reactions occurring during UV irradiation that can occur concomitantly in a single biological system: a membrane-active peptide inserted within a phospholipid bilayer. This work shows how to exploit in an original way the different reactivities of Bzp in the context of a lipid membrane, giving access to information on the CPP/lipid interaction at a molecular level such as depth of insertion or membrane fluidity in the CPP vicinity

APA, Harvard, Vancouver, ISO, and other styles

5

Chen, Tianhong, and Bjoern Reinhard. "A novel free standing lipid membrane model designed for dark field microscopy." Diffusion fundamentals 16 (2011) 32, S. 1-3, 2011. https://ul.qucosa.de/id/qucosa%3A13765.

Full text

APA, Harvard, Vancouver, ISO, and other styles

6

Chen, Tianhong, and Bjoern Reinhard. "A novel free standing lipid membrane model designed for dark field microscopy." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-184882.

Full text

APA, Harvard, Vancouver, ISO, and other styles

7

Walter, Vivien. "Lipid membrane interaction with self-assembling cell-penetrating peptides." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAE032/document.

Full text

Abstract:

Les peptides pénétrateurs de cellule (CPP) sont des oligopeptides cationiques faisant parti des vecteurs les plus étudiés dans le cadre du développement du transport ciblé de médicament à l’intérieur de l’organisme. Les applications principales sont par exemple le traitement des cancers ou la thérapie génique. Néanmoins, certaines caractéristiques des CPPs rendent leur utilisation médicale compliquée, tels que leur manque de spécificité à l’égard des cellules cibles ou la perte de leurs propriétés pénétrantes lorsqu’un cargo moléculaire leur est greffé. L’une des solutions envisagées pour résoudre ces problèmes est le greffage sur des polypeptides di-blocs auto-assemblés basés sur de l’élastine (ELPBC), des systèmes développés par l’équipe d’Ashutosh Chilkoti à l’Université de Duke (USA). Des travaux précédents ont montré que ces macromolécules, que l’on appelle CPP-ELPBC, retrouvaient les propriétés pénétrantes du CPP même en présence d’un cargo et permettaient également d’induire une spécificité à l’encontre des cellules cancéreuses. En revanche, le mécanisme de pénétration de ces systèmes restait inconnu.Dans cette thèse, je me suis concentré sur l’étude du mécanisme de pénétration des CPP et des CPP-ELPBC au travers de membranes lipidiques modèles, et en particulier sur l’adsorption de ces molécules à la surface de vésicules unilamellaires géantes (GUV). Le développement d’une nouvelle méthode de quantification de la fluorescence en microscopie confocale m’a permis de réaliser des mesures simples de comptage de peptides à la surface des vésicules, ce qui m’a permis par la suite de procéder à des mesures thermodynamiques de l’adsorption des peptides
Cell-penetrating peptides (CPP) are cationic oligopeptides currently investigated as potential vectors for targeted drug delivery design, for applications in cancer treatment and/or gene therapy. Nevertheless, some drawbacks make the CPP complex for medical applications, such as their lack of specificity toward target cells or the loss of their penetrating properties once they have been grafted with a molecular cargo. One of the solutions studied to overcome these issues is the binding of the CPP unit on a self-assembling elastin-like diblock polypeptide (ELPBC), a macromolecular system designed by the team of Ashutosh Chilkoti from Duke University (USA). While it has already been proven that these molecules, named CPP-ELPBC, recover the penetrating properties of the CPP despite the presence of a cargo and also induce a selectivity toward tumorous cells, the exact mechanism of translocation is still under debate.In this PhD thesis, I focused on the investigation of the translocation mechanism of the CPP and CPP-ELPBC using model lipid membranes, and specifically the adsorption of these molecules at the surface of giant unilamellar vesicles (GUV). The development of a new quantification method of fluorescence in confocal microscopy allowed me to directly count the peptides adsorbed on the surface of the GUVs, which I used to perform thermodynamic measurements on the peptide adsorption

APA, Harvard, Vancouver, ISO, and other styles

8

Alaimo, Cristina. "Bacterial N-glycosilation: a model to study lipid-linked oligosaccharide translocation across the membrane /." Zürich : ETH, 2006. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16728.

Full text

APA, Harvard, Vancouver, ISO, and other styles

9

Baumgart, Tobias. "Herstellung und physikochemische Charakterisierung von planaren gestützten Lipid-Modellmembran-Systemen Preparation and physicochemical characterisation of planar supported lipid model membrane systems /." [S.l.] : [s.n.], 2001. http://ArchiMeD.uni-mainz.de/pub/2001/0123/diss.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

10

Higson, Seamus P. J. "Charge transfer reactions of some naturally occuring quinones across a novel biomimetic lipid model membrane." Thesis, University of Southampton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316187.

Full text

APA, Harvard, Vancouver, ISO, and other styles

11

Lundquist, Anna. "Nanosized Bilayer Disks as Model Membranes for Interaction Studies." Doctoral thesis, Uppsala universitet, Fysikalisk kemi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8495.

Full text

Abstract:

PEG-lipid stabilized bilayer disks have been found in lipid mixtures containing polyethylene glycol (PEG)-lipids where the combination of a high bending rigidity and low PEG-lipid/lipid miscibility favours disk formation. The disks are planar and circular in shape and their long-term stability is excellent. Theoretical calculations and experimental observations suggest that the micelle forming PEG-lipid are situated at the rim of the aggregate, protecting the hydrophobic lipid chains in the bulk of the aggregate from contact with water. This thesis deals with fundamental aspects concerning the lipid distribution in the disks, as well as with development, optimization, and initial evaluation of the disks as model membranes in partition and interaction studies. Small angle neutron scattering was used to study the partial segregation of components within the bilayer disk. The experiments verified that the PEG-lipids segregate and accumulate at the bilayer disk rim. The proof of component segregation is important from a fundamental point of view and useful, as exemplified in the below-mentioned study of melittin-lipid interaction, when interpreting partition or binding data obtained from studies based on bilayer disks. Today liposomes are often used as model membranes in partition and interaction studies. Using liposomes to predict, e.g., drug partitioning can however have certain drawbacks. In this thesis the disks were proven to be attractive alternatives to liposomes as model membranes in partition studies. The formation of bilayer disks by a technique based on detergent depletion enabled incorporation of a transmembrane protein in the bilayer disks and opened up for the use of disks as model membranes in membrane protein studies. Further, bilayer disks were used in a comparative study focused on the effect of aggregate curvature on the binding of the peptide melittin. Various techniques were used to perform initial evaluations of the bilayer disks as model membranes. Of these, capillary electrophoresis and biosensor-based technology had not been used before in combination with bilayer disks.

APA, Harvard, Vancouver, ISO, and other styles

12

Ariöz, Candan. "Exploring the Interplay of Lipids and Membrane Proteins." Doctoral thesis, Stockholms universitet, Institutionen för biokemi och biofysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-102675.

Full text

Abstract:

The interplay between lipids and membrane proteins is known to affect membrane protein topology and thus have significant effect (control) on their functions. In this PhD thesis, the influence of lipids on the membrane protein function was studied using three different membrane protein models. A monotopic membrane protein, monoglucosyldiacylglyecerol synthase (MGS) from Acholeplasma laidlawii is known to induce intracellular vesicles when expressed in Escherichia coli. The mechanism leading to this unusual phenomenon was investigated by various biochemical and biophysical techniques. The results indicated a doubling of lipid synthesis in the cell, which was triggered by the selective binding of MGS to anionic lipids. Multivariate data analysis revealed a good correlation with MGS production. Furthermore, preferential anionic lipid sequestering by MGS was shown to induce a different fatty acid modeling of E. coli membranes. The roles of specific lipid binding and the probable mechanism leading to intracellular vesicle formation were also investigated. As a second model, a MGS homolog from Synechocystis sp. PCC6803 was selected. MgdA is an integral membrane protein with multiple transmembrane helices and a unique membrane topology. The influence of different type of lipids on MgdA activity was tested with different membrane fractions of Synechocystis. Results indicated a very distinct profile compared to Acholeplasma laidlawii MGS. SQDG, an anionic lipid was found to be the species of the membrane that increased the MgdA activity 7-fold whereas two other lipids (PG and PE) had only minor effects on MgdA. Additionally, a working model of MgdA for the biosynthesis and flow of sugar lipids between Synechocystis membranes was proposed. The last model system was another integral membrane protein with a distinct structure but also a different function. The envelope stress sensor, CpxA and its interaction with E. coli membranes were studied. CpxA autophosphorylation activity was found to be positively regulated by phosphatidylethanolamine and negatively by anionic lipids. In contrast, phosphorylation of CpxR by CpxA revealed to be increased with PG but inhibited by CL. Non-bilayer lipids had a negative impact on CpxA phosphotransfer activity. Taken together, these studies provide a better understanding of the significance of the interplay of lipids and model membrane proteins discussed here.

APA, Harvard, Vancouver, ISO, and other styles

13

Schumacher, Johannes [Verfasser]. "Interaction of antimicrobial compounds with lipid bilayers in established and novel membrane model systems / Johannes Schumacher." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2021. http://d-nb.info/123300901X/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Witkowski, Thomas, Rainer Backofen, and Axel Voigt. "The influence of membrane bound proteins on phase separation and coarsening in cell membranes." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-139226.

Full text

Abstract:

A theoretical explanation of the existence of lipid rafts in cell membranes remains a topic of lively debate. Large, micrometer sized rafts are readily observed in artificial membranes and can be explained using thermodynamic models for phase separation and coarsening. In live cells such domains are not observed and various models are proposed to describe why the systems do not coarsen. We review these attempts critically and show within a phase field approach that membrane bound proteins have the potential to explain the different behaviour observed in vitro and in vivo. Large scale simulations are performed to compute scaling laws and size distribution functions under the influence of membrane bound proteins and to observe a significant slow down of the domain coarsening at longer times and a breakdown of the self-similarity of the size-distribution function
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich

APA, Harvard, Vancouver, ISO, and other styles

15

Macqueen, Robin Michael. "A ²H-NMR study of lipid chain disorder in a model membrane : effect of integral peptide length." Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/26003.

Full text

Abstract:

Polypeptides of the form: Lys₂-Gly-Leu[sub n]-Lys₂-Ala-amide with n=16, 20 or 24, and of the form: Ac-Leu₁₀-Lys₂-Ala-amide, were mixed with perdeuterated potassium palmitate at peptide/lipid ratios of approximately 1:200 and 1:100. Potassium phosphate buffer (50mM) was added such that the water:lipid molar ratio was 7.75:1. ²H-NMR measurements were made on the samples at 49°C and 65°C. The effect of all peptides was to cause an increase in lipid chain order which varied linearly with concentration. This increase was manifested by an increase in average order parameter for the entire lipid chain of about 20%, from about .11 to .14.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

APA, Harvard, Vancouver, ISO, and other styles

16

Ayoub, Pierre. "Molecular dynamics study of pyrene excimer formation and oxidation in lipid bilayer models." Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAE038/document.

Full text

Abstract:

Nous proposons une nouvelle approche pour déterminer le coefficient de diffusion dans des membranes lipidiques se basant sur la formation d'excimères. Alors que les autres modèles statistiques considèrent le système comme un ensemble de points sur un réseau, nous utilisons un modèle à gros grain afin d'étudier des bicouches lipidiques simulées à l'aide du champs de force Martini. Nous déterminons le taux de réaction dépendant du temps à partir des probabilités de survie obtenues a posteriori à l'aide des trajectoires numeriques des bicouches symétriques de DOPC (1,2-Dioleoyl-sn-glycero-3-phosphocholine) et POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) simulées à 283 K et 293 K respectivement. Les dynamiques de collision sont obtenues en distinguant virtuellement les molécules simulées. Les sondes fluorescentes sont supposées semblables aux lipides, et par conséquent, ne modifient pas la dynamique. Nous obtenons une expression générale pour la probabilité de survie en combinant approximation des paires indépendantes et propriétés d'échelle, mais aucune hypothèse n'est faite pour le taux de formation d'excimère. En superposant les intensités d'émission de fluorescence normalisées, déterminées numériquement, aux courbes de titrations expérimentales, nous obtenons deux ensembles de résultats pour le coefficient de diffusion latéral, selon que l'association entre feuillets est autorisée ou pas. Nous utilisons un rayon de capture de 0.5 nm, la distance à partir de laquelle les deux sondes réagissent pour former un excimère. En comparant la dynamique Martini aux expériences de fluorescence, il est possible d'estimer le facteur d'accélération
We propose a novel approach to extract the lateral diffusion coefficient in lipid bilayers using excimer formation. In contrast to previous statistical models that modeled the system as points undergoing jumps from site to site on a lattice, we use coarse-grained molecular dynamics to study lipid bilayers simulated using the Martini force field. We derive time dependent reaction rates from survival probabilities obtained a posteriori from numerically generated trajectories of symmetric DOPC (1,2-Dioleoyl-sn-glycero-3-phosphocholine) and POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) bilayers at 283K and 293K respectively. Collision dynamics are determined by virtually relabeling the simulated molecules. The fluorescent probes are assumed to behave like ordinary membrane lipids and therefore the dynamics remain unaffected. We derive a generalized expression for the survival probability combining independent pairs and size scaling assumptions, but no assumption is made regarding the kinetic rate of the excimer formation process. By fitting the numerically determined normalized fluorescence emission intensities to experimental titration curves, we obtain two sets of results for the lateral diffusion coefficients depending whether interleaflet excimer association is allowed or not. We use a capture radius of 0.5 nm, the distance at which the probes react to form excimers. By relating Martini dynamics to real fluorescence experiments, we estimate the numerical Martini acceleration factor. We also study mixtures of oxidized-non oxidized DOPC and POPC bilayers using a hydroperoxidized model of these lipids for different concentrations of the oxidized component (3.1%, 25% and 50%). Using pair correlation functions, we extract structural information on the systems and determine whether the two components are prone to mixing or not. Finally, we calculate the thermodynamic mixing parameters within the framework of the virial expansion

APA, Harvard, Vancouver, ISO, and other styles

17

Witkowski, Thomas, Rainer Backofen, and Axel Voigt. "The influence of membrane bound proteins on phase separation and coarsening in cell membranes." Royal Society of Chemistry, 2012. https://tud.qucosa.de/id/qucosa%3A27814.

Full text

Abstract:

A theoretical explanation of the existence of lipid rafts in cell membranes remains a topic of lively debate. Large, micrometer sized rafts are readily observed in artificial membranes and can be explained using thermodynamic models for phase separation and coarsening. In live cells such domains are not observed and various models are proposed to describe why the systems do not coarsen. We review these attempts critically and show within a phase field approach that membrane bound proteins have the potential to explain the different behaviour observed in vitro and in vivo. Large scale simulations are performed to compute scaling laws and size distribution functions under the influence of membrane bound proteins and to observe a significant slow down of the domain coarsening at longer times and a breakdown of the self-similarity of the size-distribution function.
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

APA, Harvard, Vancouver, ISO, and other styles

18

Troup, Gregory Marshall Wrenn Steven Parker Dr. "Fluorescence investigation of laterally phase-separated cholesterol rich domains in model lipid membranes using the membrane probe 1-myristoyl-2-[12-[(5-dimethylamino-1-naphthalenesulfonyl)amino]dodecanoyl]-sn-Glycero-3-phosphocholine (A) /." Philadelphia, Pa. : Drexel University, 2004. http://dspace.library.drexel.edu/handle/1860/345.

Full text

APA, Harvard, Vancouver, ISO, and other styles

19

De, Ghellinck D'Elseghem Alexis. "Natural and model membranes: structure and interaction with bio-active molecules via neutron reflection." Doctoral thesis, Universite Libre de Bruxelles, 2013. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209550.

Full text

Abstract:

Dans cette thèse de doctorat, la structure de membranes naturelles et modèles et leurs interactions avec des molécules biologiquement actives ont été étudiées au moyen de la réflectométrie de neutrons. Les lipides naturels ont été extraits de la levure Pichia pastoris, poussée en milieux deutéré et hydrogéné. L’analyse a montré que la quantité relative de phospholipides n’est pas affectée par le changement en composition isotopique du milieu de croissance. Cependant, les cellules de levures deutérées contiennent principalement des acides gras C18 :1 alors que le degré d’insaturation est plus élevé chez les levures hydrogénés. Diminuer la température du milieu de croissance permet d’augmenter le degré d’insaturation des acides gras chez les levures deutérées. Une analyse qualitative des sphingolipides a été réalisée et un protocole pour séparer les fractions phosphocholines et phosphoethanolamine a été établi.

La structure de bicouches composées des lipides de levures a été étudiée par réflectivité de neutrons. La bicouche composée de lipides deutérés polaires a une épaisseur similaire aux bicouches faites de phosphocholines C18:1 synthétiques. En présence de stérols, la rugosité aux interfaces entre les têtes polaires et les chaînes augmente. La bicouche composée de lipides polaires hydrogénés est plus mince que celle deutérée. Ceci est dû à la composition en acides gras beaucoup plus variée et du plus grand nombre d’insaturations. En présence de stérols, l’épaisseur de la bicouche hydrogénée augmente.

L’interaction de ces bicouches avec l’amphotéricine B (AmB) a été étudiée. L’AmB est un antifongique qui interagit fortement avec les membranes contenant de l’ergostérol et moins fortement avec des membranes contenant du cholestérol. Dans tous les cas, les molécules d’AmB forment une couche épaisse et diluée au dessus de la bicouche lipidique. En présence de stérols, les molécules d’AmB pénètrent dans la bicouche et change sa structure selon la composition en acide gras.

La structure de bicouches lipidiques de plante et leurs interactions avec des intermédiaires de synthèse ont aussi été étudiées par réflectivité de neutrons. Des mélanges ternaires de plantes étaient déposés sur silicium et des mélanges quaternaires sur saphir. L’épaisseur de la bicouche composée de mélange ternaire est de 38 Å, tandis que celle du mélange ternaire est de 28 Å, la différence venant probablement d’un effet de substrat. La présence de diacylglycérol (DAG) a comme conséquence d’augmenter l’aire par lipide, et ainsi de changer la conformation des têtes polaires. L’interaction des bicouches de lipide de plante avec l’acide phosphatidique (PA) dans le but d’observer un flip-flop possible a aussi été étudiée mais le PA a tendance à désorbé les bicouches du substrat et aucun mécanisme de flip flop n’a été détecté.

Finalement, la localisation d’une petite molécule, le resvératrol, dans des bicouches modèles a été étudiée. Le resvératrol est connu pour être responsable du « paradoxe français » qui est une corrélation inverse entre la consommation d’aliment gras et un faible taux de maladie cardiaque. Quand le resvératrol est adsorbé à partir de la phase liquide, il induit une réorganisation des têtes polaires. Quand il est déposé sur le substrat en présence des lipides, il est présent à l’interface entre les têtes polaires et les chaines.

Doctorat en Sciences
info:eu-repo/semantics/nonPublished

APA, Harvard, Vancouver, ISO, and other styles

20

SAITTA, FRANCESCA. "THERMODYNAMIC STABILITY OF ISG-LIKE MODEL LIPID MEMBRANES: INSPECTING THE CONTRIBUTIONS OF LIPID-LIPID INTERACTION AND ACTION OF FREE FATTY ACIDS IN THE FRAME OF TYPE 2 DIABETES MELLITUS DISEASE." Doctoral thesis, Università degli Studi di Milano, 2019. http://hdl.handle.net/2434/692503.

Full text

Abstract:

Allo scopo di comprendere il ruolo giocato da alcuni dei principali fattori che contribuiscono alla stabilità termodinamica delle membrane cellulari, è stato effettuato uno studio progressivo di vescicole con diversa morfologia e composizione lipidica a pH fisiologico mediante calorimetria a scansione differenziale ad alta sensibilità (High-Sensitivity DSC), raggiungendo la preparazione di vescicole lipidiche artificiali che rappresentano abbondantemente il doppio strato fosfolipidico dei granuli secretori di insulina (ISGs), vescicole presenti nelle cellule β di Langerhans del pancreas e addette alla conservazione e cosecrezione di insulina e amilina in seguito al consumo di alimenti. Tutte le vescicole sono state preparate allo scopo di rappresentare solamente la componente lipidica delle membrane delle ISGs, ovvero il bilayer fosfolipidico, ma per motivi di semplicità saranno tutte indicate come “membrane modello” in questa tesi. Gli effetti della curvatura di membrana sono stati considerati analizzando i profili micro-DSC di vescicole unilamellari piccole, grandi e giganti preparate come sistemi puri e misti di DMPC, DPPC e DSPC. Lo studio incrociato di sistemi binari composti da DMPC, DPPC, DSPC e DPPC, DPPS, DPPE ha consentito la discriminazione dei ruoli giocati dalle diverse teste e code fosfolipidiche riguardo al comportamento termotropico delle membrane cellulari, mentre l’aggiunta di DOPC, un fosfolipide insaturo, ad una membrane ternaria completamente satura e caratterizzata da solo una specifica testa fosfolipidica (colina) ha rivelato la forte influenza che le code insature hanno sull’organizzazione dei lipidi in membrana. Quindi, è stato possibile delineare una gerarchia di contributi alla stabilità complessiva delle membrane: curvatura di membrana < testa fosfolipidica < coda fosfolipidica < insaturazione fosfolipidica. La successiva inclusione di sfingomieline e lisofosfatidilcoline alla membrana ternaria DPPC:DPPE:DPPS, la cui composizione rifletteva già le proporzioni delle ISGs, insieme ad una distribuzione più completa di acidi grassi presenti nel bilayer fosfolipidico delle ISGs ha permesso di giungere alla preparazione di una membrana modello complessa costituita da quattordici componenti che riflette l’80% dei fosfolipidi presenti nel sistema reale. Infine, è stata considerata anche l’inclusione del colesterolo portando all’ottenimento della membrana simil-ISG finale. L’effetto di acidi grassi liberi (FFAs), i cui livelli sono spesso elevati in soggetti diabetici e/o obesi, sulla stabilità termodinamica di membrane selezionate è stato inoltre investigato. I risultati hanno evidenziato forti effetti stabilizzanti sulle membrane e pronunciate segregazioni di fase nel caso di acidi saturi (acidi palmitico e stearico), moderati effetti stabilizzanti per un acido insaturo trans (acido elaidico), mentre effetti opposti sono stati riscontrati per un acido insaturo cis (acido oleico). Infine, sono state effettuate misure calorimetriche e spettroscopiche allo scopo di investigare l’interazione tra membrane modello e un peptide in grado di formare pori (nisina). A tale scopo, è stata progettata una membrana modello semplificata rappresentante la termodinamica della membrana simil-ISG combinando specifiche percentuali di DMPC, DPPS e DOPC. L’interazione nisina-membrana è stata studiata sulla membrana semplificata mediante micro-DSC, anisotropia di fluorescenza e DLS a pH fisiologico, evidenziando inoltre il ruolo di sei diversi FFAs sull’interazione peptide-membrana, ossia due FFAs saturi (acidi palmitico e stearico), due monoinsaturi (acido oleico come acido insaturo cis e acido elaidico come acido insaturo trans) e due acidi grassi polinsaturi (l’acido linoleico come ω-6 e l’acido docosaesaenoico o DHA come ω-3).
A stepwise study of vesicles with different morphology and lipid composition was performed through high-sensitivity differential scanning calorimetry at physiological pH with the purpose of comprehending the role played by some of the main factors that contribute to the thermodynamic stability of cell membranes, achieving the preparation of artificial lipid vesicles that highly resembled the phospholipid bilayer of Insulin Secretory Granules (ISGs), vesicles located in the pancreatic Langerhans β-cells and which are responsible for insulin and amylin storage and secretion in response to nutrient intake. All the considered vesicle preparations were aimed at representing only the lipid component of ISGs membrane, i.e. the phospholipid bilayer, but we will refer to all as “model membranes” in this thesis for simplicity’ sake. Curvature effects were considered by analysing the micro-DSC profiles of small, large and giant unilamellar vesicles prepared as pure and mixed systems of DMPC, DPPC, DSPC. The cross-study of binary systems composed by DMPC, DPPC, DSPC and DPPC, DPPS, DPPE allowed the dissection of the role played by several phospholipid headgroups and tails on the thermotropic behaviour of cell membranes, whilst the addition of DOPC, an unsaturated phospholipid, to a completely saturated ternary membrane characterized by only a specific phospholipid headgroup (choline) revealed the strong influence of unsaturated tails on membrane lipid organization. Therefore, a hierarchy of contribution to the overall thermodynamic stability of membranes was depicted as membrane curvature < phospholipid headgroup < phospholipid tail < phospholipid unsaturation. The following inclusion of sphingomyelins and lysophosphatidylcholines to a DPPC:DPPE:DPPS ternary membrane, whose composition already reflected the proportions in ISGs, together with a more complete fatty acids distribution characterizing the phospholipid bilayer of the ISGs allowed us to achieve the preparation of a high-complexity fourteen-components model membrane that reflected the 80% of phospholipids present in such a real system. The inclusion of cholesterol was finally considered for the achievement of the final ISG-like membrane. Furthermore, the effect of Free Fatty Acids (FFAs), whose levels are recurrently altered in diabetic and/or obese subjects, on the thermodynamic stability of selected membranes was investigated. The results highlighted strong stabilizing effects on the membranes as well as pronounced phase segregations in the case of saturated acids (palmitic and stearic acids), moderate stabilizing effects for a trans-unsaturated FFA (elaidic acid), whereas the opposite effect was observed in the case of a cis-unsaturated one (oleic acid). Finally, in order to investigate the interaction between model membranes and a pore-forming peptide (nisin), calorimetric and spectroscopic measurements were carried out. With this purpose, a simplified model membrane that resembled the thermodynamics of the ISG-like membrane was modelled by combining specific percentages of DMPC, DPPS and DOPC. Nisin-membrane interaction was studied on the simplified membrane through micro-DSC, fluorescence anisotropy and DLS at physiological pH, also highlighting the role of six different FFAs on peptide-membrane interaction, namely two saturated FFAs (palmitic and stearic acids), two monounsaturated FFAs (the cis-unsaturated oleic acid and the trans-unsaturated elaidic acid) and two polyunsaturated FFAs (the ω-6 linoleic acid and the ω-3 docosahexaenoic acid or DHA).

APA, Harvard, Vancouver, ISO, and other styles

21

Pähler, Gesa. "Lateral Organization and Thermodynamics of Coiled-coil Lipopeptides - Implications for Docking and Fusion Efficiency." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2012. http://hdl.handle.net/11858/00-1735-0000-000D-F19D-5.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

Wong, Christine Shiang Yee. "Study on lipid droplet dynamics in live cells and fluidity changes in model bacterial membranes using optical microscopy techniques." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/8842.

Full text

Abstract:

In this thesis optical microscopy techniques are used to consider aspects of viral and bacterial infections. In part 1, the physical effects of cytomegalovirus on lipid droplet dynamics in live cells are studied; in part 2, the effects of an antimicrobial peptide on the fluidity of model bacterial membranes are studied. The optical microscopy techniques used to study the effects of murine-cytomegalovirus (mCMV) on lipid droplets in live NIH/3T3 fibroblast cells in real-time are coherent anti- Stokes Raman scattering (CARS), two-photon fluorescence (TPF) and differential interference contrast (DIC) microscopies. Using a multimodal CARS and TPF imaging system, the infection process was monitored by imaging the TPF signal caused by a green fluorescent protein (GFP)-expressing strain of mCMV, where the amount of TPF detected allowed distinct stages of infection to be identified. Meanwhile, changes to lipid droplet configuration were observed using CARS microscopy. Quantitative analysis of lipid droplet numbers and size distributions were obtained from live cells, which showed significant perturbations as the infection progressed. The CARS and TPF images were acquired simultaneously and the experimental design allowed incorporation of an environmental control chamber to maintain cell viability. Photodamage to the live cell population was also assessed, which indicated that alternative imaging methods must be adopted to study a single cell over longer periods of time. To this end, DIC microscopy was used to study the lipid droplet dynamics, allowing lipid droplet motion to be tracked during infection. In this way, the effects of viral infection on the mobility and arrangement of the lipid droplets were analysed and quantified. It was found that the diffusion coefficient of the lipid droplets undergoing diffusive motion increased, and the droplets undergoing directed motion tended to move at greater speeds as the infection progressed. In addition, the droplets were found to accumulate and cluster in infected cells. The second part of this thesis presents a study on the effects of an antimicrobial peptide on model bacterial membranes. Giant unilamellar vesicles (GUVs) were produced as a simple model of E. Coli membrane using a 3:1 mixture of DPPC and POPG lipids. Incorporating Laurdan fluorescent dye into the lipid membrane of the GUVs allowed the membrane fluidity to be probed and visualised using TPF microscopy, whereby the fluidity was quantified by determining the general polarization (GP) values. Studying GUVs comprising single lipid and mixed lipid compositions over a temperature range from 25 C to 55 C enabled the lipid phase bands to be identified on the basis of GP value as gel phase and liquid crystalline phase. As such, the changes in lipid phase as a result of interaction with AMP were quantified, and phase domains were identified. It was found that the amount of liquid crystalline phase domains increased significantly as a result of AMP interaction.

APA, Harvard, Vancouver, ISO, and other styles

23

Gleisner, Martin. "Interaction of he Epsin N-Terminal Homology domain (ENTH) with artificial membranes as a function of lateral tension." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2016. http://hdl.handle.net/11858/00-1735-0000-0028-8821-2.

Full text

Abstract:

Proteine formen während der Endozytose planare Membranen zu gekrümmten Vesikeln um. Im ersten Schritt dieses Prozesses bindet das Protein Epsin an das Rezeptorlipid Phosphatidylinositol-4,5-bisphosphat (PIP₂) und ein vorher ungeordneter Bereich am N-Terminus von Epsin, die epsin N-terminal homology domain (ENTH), bildet eine α-Helix, welche in die Membran insertiert. Im Rahmen dieser Arbeit wurde die Wechselwirkung von ENTH mit PIP₂-haltigen Lipiddoppelschichten unter Verwendung von bottom up Modellsystemen charakterisiert. Die Affinität von ENTH zu PIP₂ wurde für verschiedene Lipidzusammensetzungen und Membrangeometrien untersucht, wobei unabhängig von Lipidzusammensetzung und Membrantopologie ähnliche Bindungskonstanten im hohen nanomolaren Bereich bestimmt wurden. Ausgestülpte porenüberspannende Membranen wurden als Modellsystem etabliert, um die Fähigkeit von ENTH zur Membrankrümmung als Funktion der Lipidzusammensetzung zu charakterisieren. Die Höhe der ausgestülpten Membranen ist durch die laterale Spannung begrenzt. Verursacht durch Insertion der ENTH Helix wuchsen Membranen mit einem hohen Flächenkompressionsmodul. Im Gegensatz dazu rissen Membranen mit einem niedrigen Flächenkompressionsmodul durch die ENTH induzierte Bildung von Membrandefekten. Entgegen der Eigenschaft von ENTH Membranen zu krümmen, wurde an hochgespannten porenüberspannenden Membranen keine Membrantubulierung und -vesikulierung beobachtet. Daher wurde untersucht, ob diese Fähigkeit durch eine hohe laterale Spannung unterdrückt wird. Zu diesem Zweck wurden Riesenvesikel auf einem Glassubstrat adhäriert, wobei die Adhäsionsstärke und in Folge die laterale Spannung als Funktion der Mg²⁺ Konzentration eingestellt werden konnte. ENTH-induzierte Membrantubulierung konnte für Vesikel mit niedriger Spannung nachgewiesen werden und war bei höherer Spannung unterdrückt. Unabhängig von der Membranspannung wurde ein Abflachen der Vesikel nach ENTH-Zugabe beobachtet. Die Ursache hierfür wurde in der durch die insertierte Helix hervorgerufene Reduktion des Flächenkompressionsmoduls gefunden. Die insertierte Helix stört die hydrophoben Wechselwirkungen der Lipidfettsäureketten und das reduzierte Flächenkompressionsmodul verringert die zur Membrankrümmung benötigte Energie. In Kombination mit der durch die insertierte Helix erzeugten lokalen Krümmung ist dies eine molekulare Erklärung für die ENTH-initiierte Bildung eines Vesikels während der Endozytose.

APA, Harvard, Vancouver, ISO, and other styles

24

Guidi, Henrique Santos. "Modelos estatísticos para a transição ordem - desordem de camadas lipídicas." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-27032013-130925/.

Full text

Abstract:

Lipídios em solução aquosa formam uma variedade de estruturas diferentes que incluem monocamadas de surfactantes na interface água-ar, conhecidas como monocamadas de Langmuir, como também vesículas unilamelares ou plurilamelares no interior da solução. Sob variação de temperatura, estas estruturas apresentam diferentes fases, observadas através de calorimetria ou variação isotérmica de pressão lateral. Entre as fases apresentadas por estas estruturas, as duas mais importantes se diferenciam pela ordem das cadeias lipídicas. Entendemos que do ponto de vista das fases termodinâmicas, simplificado e qualitativo, monocamadas de Langmuir e bicamadas lipídicas constituem o mesmo sistema físico sob vínculos diferentes. Neste trabalho, desenvolvemos um modelo estatístico para o estudo da transição ordem-desordem destes sistemas, que inclui flutuações de densidade, estas ausentes no modelo de Doniach, de 1980, a base para muitos estudos teóricos para transições de fase de sistemas lipídicos. Flutuações de densidade são fundamentais na descrição de vesículas lipídicas carregadas, compostas de surfactante cuja cabeça polar se dissocia em água. O estudo em laboratório das propriedades térmicas e estruturais de membranas artificiais de lipídios carregados _e relativamente recente, e foi desenvolvido em grande parte no Laboratório de Biofísica do IFUSP. Tais membranas apresentam comportamento distinto das membranas neutras, notoriamente influenciado pela concentração de sal na solução. Isto motivou o desenvolvimento de uma segunda versão do modelo, na qual passamos a descrever a cabeça polar do lipídio em termos de um par de cargas opostas, sendo que a camada lipídica foi acoplada ao modelo primitivo restrito na rede, que desempenha o papel da solução salina. O primeiro modelo foi estudado por aproximação de campo médio e por simulações de Monte Carlo, e o segundo modelo foi investigado apenas através de simulações numéricas. O estudo do modelo carregado foi precedido por uma investigação criteriosa das técnicas de simulação de sistemas com interação Coulombiana, resultando no desenvolvimento de uma metodologia adequada a condições de contorno não isotrópicas e com custo computacional reduzido. Os modelos estatísticos propostos por nós levaram a dois resultados importantes. O modelo para camadas lipídicas neutras é, até hoje, o único modelo estatístico que descreve tanto a transição gel-fluido de bicamadas lipídicas, como a transição líquido condensado - líquido expandido\" de monocamadas de Langmuir, além de descrever também a transição líquido expandido gás na interface água-ar. O modelo para camadas lipídicas que se dissociam em água reproduz a variação abrupta na dissociação, concomitante com a transição ordem-desordem, propriedade que permite interpretar estudos experimentais relativos à condutividade das soluções lipídicas correspondentes.
Lipids in aqueous solution form a variety of different structures which include monolayers of surfactants at the water-air interface, known as Langmuir monolayers, as well as unilamellar or plurilamellar vesicles within the solution. Under temperature variation, these structures display different phases, observed through calorimetry or isothermal variation of lateral pressure. Among the phases presented by these structures, the two most important differ in the order of the lipid chains. From the point of view of the thermodynamic phases, our understanding is that Langmuir monolayers and lipid bilayers constitute the same physical system under different constraints. In this work, we develop a statistical model for the order - disorder transition of lipid bilayers which adds density fluctuations to Doniach\'s 1980 model, which has been considered the basis for many theoretical studies for lipid systems phase transitions. Density fluctuations are essential in the description of the properties of charged vesicles in solution, which consist of surfactants whose polar head dissociates in water. The study in the laboratory of thermal and structural properties of artificial charged lipid membranes is relatively new, and was developed largely in the IFUSP Laboratory of Biophysics. Such membranes exhibit distinct behavior if compared to neutral membranes, notoriously influenced by the solution salt concentration. The experimental investigations motivated us to develop a second model, in which we describe the polar headgroups through a pair of opposite charges. The lipid layer is attached to the lattice restricted primitive model, which plays the role of the saline solution. The first model was studied both through a mean-field approximation as well as through Monte Carlo simulations, whereas the second model was investigated only through numerical simulations. The study of the charged model was preceded by a thorough investigation of the simulation techniques for Coulomb interaction systems, leading to the development of a methodology suitable for non isotropic boundary conditions and with reduced computational cost. The statistical models proposed by us led to two important results. To our knowledge, our model for neutral lipid layers is the only statistical model which, aside from describing simultaneously both the gel-fluid transition of lipid bilayers and the condensed liquid - expanded liquid transition of Langmuir monolayers, also describes the gas- expanded liquid transition at the air-water interface. The model for lipid layers that dissociate in water reproduces the abrupt change in dissociation, concomitant with the order-disorder transition, a property that allows us to interpret experimental studies related to conductivity of the corresponding lipid solutions.

APA, Harvard, Vancouver, ISO, and other styles

25

Gräb, Oliver. "Solid Supported Model Membranes Containing Plant Glycolipids: A Tool to Study Interactions between Diatom Biomolecules and the Silicalemma in vitro." Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2017. http://hdl.handle.net/11858/00-1735-0000-0023-3E88-E.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

Vogel, Alexander, Jörg Nikolaus, Katrin Weise, Gemma Triola, Herbert Waldmann, Roland Winter, Andreas Herrmann, and Daniel Huster. "Interaction of the human N-Ras protein with lipid raft model membranes of varying degrees of complexity." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-191006.

Full text

Abstract:

Ternary lipid mixtures composed of cholesterol, saturated (frequently with sphingosine backbone), and unsaturated phospholipids show stable phase separation and are often used as model systems of lipid rafts. Yet, their ability to reproduce raft properties and function is still debated. We investigated the properties and functional aspects of three lipid raft model systems of varying degrees of biological relevance – PSM/POPC/Chol, DPPC/POPC/Chol, and DPPC/DOPC/Chol – using 2H solidstate nuclear magnetic resonance (NMR) spectroscopy, fluorescence microscopy, and atomic force microscopy. While some minor differences were observed, the general behavior and properties of all three model mixtures were similar to previously investigated influenza envelope lipid membranes, which closely mimic the lipid composition of biological membranes. For the investigation of the functional aspects, we employed the human N-Ras protein, which is posttranslationally modified by two lipid modifications that anchor the protein to the membrane. It was previously shown that N-Ras preferentially resides in liquid-disordered domains and exhibits a time-dependent accumulation in the domain boundaries of influenza envelope lipid membranes. For all three model mixtures, we observed the same membrane partitioning behavior for N-Ras. Therefore, we conclude that even relatively simple models of raft membranes are able to reproduce many of their specific properties and functions.

APA, Harvard, Vancouver, ISO, and other styles

27

Vogel, Alexander, Jörg Nikolaus, Katrin Weise, Gemma Triola, Herbert Waldmann, Roland Winter, Andreas Herrmann, and Daniel Huster. "Interaction of the human N-Ras protein with lipid raft model membranes of varying degrees of complexity." de Gruyter, 2014. https://ul.qucosa.de/id/qucosa%3A14050.

Full text

Abstract:

Ternary lipid mixtures composed of cholesterol, saturated (frequently with sphingosine backbone), and unsaturated phospholipids show stable phase separation and are often used as model systems of lipid rafts. Yet, their ability to reproduce raft properties and function is still debated. We investigated the properties and functional aspects of three lipid raft model systems of varying degrees of biological relevance – PSM/POPC/Chol, DPPC/POPC/Chol, and DPPC/DOPC/Chol – using 2H solidstate nuclear magnetic resonance (NMR) spectroscopy, fluorescence microscopy, and atomic force microscopy. While some minor differences were observed, the general behavior and properties of all three model mixtures were similar to previously investigated influenza envelope lipid membranes, which closely mimic the lipid composition of biological membranes. For the investigation of the functional aspects, we employed the human N-Ras protein, which is posttranslationally modified by two lipid modifications that anchor the protein to the membrane. It was previously shown that N-Ras preferentially resides in liquid-disordered domains and exhibits a time-dependent accumulation in the domain boundaries of influenza envelope lipid membranes. For all three model mixtures, we observed the same membrane partitioning behavior for N-Ras. Therefore, we conclude that even relatively simple models of raft membranes are able to reproduce many of their specific properties and functions.

APA, Harvard, Vancouver, ISO, and other styles

28

Basiouni, Shereen. "The modulating effects of polyunsaturated fatty acids on membrane composition and phospholipase D in a canine mast cell line as a model for atopic dermatitis." Doctoral thesis, Universitätsbibliothek Leipzig, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-142529.

Full text

Abstract:

Polyunsaturated fatty acids (PUFA) have been used with some success in the treatment of canine atopic dermatitis (CAD). Correspondent in vitro studies revealed that PUFA play a crucial role in the exocytosis of mast cells. n3 PUFA such as α-linolenic acid (LNA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), as well as the n6 PUFA linoleic acid (LA) have been shown to arrest the secretion of inflammatory mediators. Contrary, the n-6 PUFA arachidonic acid (AA) has been proven to promote the production of mast cell inflammatory mediators. However, we are still lacking a complete picture of the mode of action. The goal of this work was to further characterize the modulatory effects of PUFA supplementation on the plasma membrane lipid composition of mast cells. Furthermore the consequences of a membrane modulation of mast cells by PUFA on the localization and activity on of the membrane bound enzyme phospholipases D (PLD) were investigated. Canine mastocytoma cells (C2) were supplemented with one of the following PUFA: LNA, EPA, DHA, LA or AA. To investigate the influence of PUFA on the lipid composition of membrane microdomains, lipid rafts were separated from non-raft plasma membranes of mast cells for the first time using a detergent-free isolation technique. Results show that PUFA are significantly increased in rafts as well as in non-rafts microdomains (Publication 1). The incorporation of PUFA into the membrane goes along with an increase of the unsaturation status and the fluidity of the membrane. This rise in membrane fluidity may result in a reorganization of membrane signaling molecules and enzymes such as the PLD. To define the impact of a PUFA supplementation on PLD trafficking, C2 were transfected with green fluorescent protein (GFP) fusion plasmids encoding PLD1 or PLD2. Since the transfection ability of the suspension cell line C2 is limited, a special transfection protocol was established, suitable for non-adherent cell lines. Transfection succeeded using chicken egg white as coating material for the cell culture plates. The transfection efficiency rose to 50% versus 5% in uncoated plates. In addition to the obvious increase in the transfection efficiency, the new technique is simple and economic and might be suitable for a wide range of suspension cell lines (Publication 2). Using this optimized protocol the influence of PUFA on the trafficking of PLD isoforms was studied. LNA, EPA, DHA and LA but not AA prevented the stimulation-induced translocation of PLD1 to the plasma membrane. Since the translocation of PLD1 is important for mast cell exocytosis, LNA, EPA, DHA and LA do have an inhibiting effect on the stimulation-induced release of pro-inflammatory mediators. All PUFA tested boosted the total PLD activity. In order to rule out, which PLD isoform was affected by the PUFA, the mast cells were supplemented with DHA or AA in the presence of specific PLD isoform inhibitors. DHA completely abolished the inhibitiory effect of the PLD1 inhibitor but had no effect on the inhibitory effect of PLD2 inhibitor. On the other hand, AA suppressed the inhibitory effect of both PLD1 and PLD2 inhibitor (Publication 3). Taking together, the studies provide a mechanistic base for the role of PUFA in the exocytosis processes of mast cells. PUFA of the n3 and the n6 families impact the lipid composition of membrane microdomains, which in turn lead to a modulation of the physiochemical properties of the membrane. LNA, EPA, DHA and LA suppress the release of inflammatory mediators through their inhibitory action on the stimulation-induced translocation of the PLD1. Contrariwise, AA permits the stimulation-induced migration of PLD1 to the plasma membrane and increases the activity of both PLD isoforms. Therefore, LNA, EPA, DHA and LA but not AA inhibit the release of mast cell inflammatory mediators upon stimulation
Mehrfach ungesättigte Fettsäuren (PUFA) können mit einigem Erfolg zur Behandlung der caninen atopischen Dermatitis (CAD) eingesetzt werden. In vitro-Studien zeigten, dass PUFA eine entscheidende Rolle in der Exozytose von Mastzellen spielen. N-3-PUFA wie α-Linolensäure (LNA), Eicosapentaensäure (EPA), Docosahexaensäure (DHA) sowie die n-6-PUFA Linolsäure (LA) können die Sekretion von Entzündungsmediatoren vermindern. Arachidonsäure (AA) als n-6 mehrfach ungesättigte Fettsäure hingegen fördert die Entzündungsmediatoren-Freisetzung aus den Mastzellen. Eine vollständige Aufklärung der Wirkungsweise fehlt aber weiterhin. Das Ziel dieser Arbeit war eine weitergehende Charakterisierung der modulierenden Effekte einer PUFA-Supplementierung auf die Lipidzusammensetzung der Plasmamembran von Mastzellen. Darüber hinaus wurden die Auswirkungen von PUFA auf die Lokalisation und Aktivität des Membran-gebundenen Enzyms Phospholipase D (PLD) untersucht. Canine Mastozytom-Zellen (C2) wurden mit einer der folgenden PUFA kultiviert: LNA, EPA, DHA, LA oder AA. Um den Einfluss von PUFA auf die Lipidzusammensetzung der Membran-Mikrodomänen zu untersuchen, konnten sowohl Lipid Raft als auch Nicht-Raft Plasmamembran-Anteile von Mastzellen zum ersten Mal mittels einer Detergenzien-freien Isolationsmethode getrennt werden. Hervorzuheben ist, dass PUFA signifikant vermehrt in Raft- sowie in Nicht-Raft Membranmikrodomänen eingelagert werden (Publikation 1). Die Integration von PUFA in die Membran geht mit einer Steigerung der Doppelbindungsanzahl und der Fluidität der Membran einher. Diese Erhöhung der Membranfluidität kann zu einer Reorganisation von membranären Signalmolekülen und Enzymen wie der PLD führen. Um die Auswirkungen einer PUFA-Supplementierung auf den intrazellulären Transport der PLD in C2 zu bestimmen, wurden die Zellen mit PLD1- oder PLD2-codierenden grün fluoreszierenden Protein-(GFP-)Fusionsplasmiden transfiziert. Da die Transfektionsfähigkeit der Suspensions-Zelllinie C2 begrenzt ist, wurde ein für nicht-adhärente Zelllinien geeignetes Transfektionsprotokoll etabliert. Mit Hühnereiweiß als Beschichtungsmaterial für die Zellkultur-Platten stieg die Transfektionseffizienz auf 50% im Vergleich zu 5% bei unbeschichteten Platten. Neben der deutlichen Erhöhung der Transfektionseffizienz ist die neu etablierte Technik einfach durchzuführen sowie wirtschaftlich und kann für eine Vielzahl von Suspension-Zelllinien geeignet sein (Publikation 2). Unter Verwendung dieses optimierten Protokolls wurde der Einfluss von PUFA auf die Translokation der PLD-Isoformen untersucht. LNA, EPA, DHA und LA, nicht aber AA verhindern die stimulationsinduzierte Translokation der PLD1 an die Plasmamembran. Die Translokation der PLD1 ist wichtig für die Mastzell-Exozytose. LNA, EPA, DHA und LA haben hier eine hemmende Wirkung auf die stimulationsinduzierte Freisetzung von proinflammatorischen Mediatoren. Alle getesteten PUFA verstärken die Gesamt-PLD-Aktivität. Um zu unterscheiden, welche PLD-Isoform durch PUFA beeinflusst ist, wurden die Mastzellen mit DHA oder AA in Gegenwart von PLD-Isoform-Inhibitoren supplementiert. DHA hebt die inhibitorische Wirkung des PLD1-Inhibitors vollständig auf, zeigte aber keinen Einfluss auf die hemmende Wirkung des PLD2-Inhibitors. Andererseits unterdrückt AA die hemmende Wirkung des PLD1- als auch des PLD2-Inhibitors (Publikation 3). Zusammenfassend bietet die Studie eine mechanistische Basis für die Rolle von PUFA bei Exozytose-Prozessen von Mastzellen. PUFA der n-3- und n-6-Familie beeinflussen die Lipidzusammensetzung von membranären Mikrodomänen, was wiederum zu einer Modulation der physikalisch-chemischen Eigenschaften der Membran führt. LNA, EPA, DHA und LA verhindern die Freisetzung von Entzündungsmediatoren durch ihre hemmende Wirkung auf die stimulationsinduzierte Translokation der PLD1. Umgekehrt erlaubt AA eine stimulationsinduzierte Migration der PLD1 zur Plasmamembran und steigert die Aktivität der beiden Isoformen der PLD. Somit hemmen LNA, EPA, DHA und LA, aber nicht AA die Freisetzung von Mastzell-Entzündungsmediatoren nach Stimulation

APA, Harvard, Vancouver, ISO, and other styles

29

Liebau, Jobst. "Taming the Griffin : Membrane interactions of peripheral and monotopic glycosyltransferases and dynamics of bacterial and plant lipids in bicelles." Doctoral thesis, Stockholms universitet, Institutionen för biokemi och biofysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-146872.

Full text

Abstract:

Biological membranes form a protective barrier around cells and cellular compartments. A broad range of biochemical processes occur in or at membranes demonstrating that they are not only of structural but also of functional importance. One important class of membrane proteins are membrane-associated glycosyltransferases. WaaG is a representative of this class of proteins; its function is to catalyze one step in the synthesis of lipopolysaccharides, which are outer membrane lipids found in Gram-negative bacteria. To study protein-membrane complexes by biophysical methods, one must employ membrane mimetics, i.e. simplifications of natural membranes. One type of membrane mimetic often employed in solution-state NMR is small isotropic bicelles, obloid aggregates formed from a lipid bilayer that is dissolved in aqueous solvent by detergent molecules that make up the rim of the bicelle. In this thesis, fast dynamics of lipid atoms in bicelles containing lipid mixtures that faithfully mimic plant and bacterial membranes were investigated by NMR relaxation. Lipids were observed to undergo a broad range of motions; while the glycerol backbone was found to be rigid, dynamics in the acyl chains were much more rapid and unrestricted. Furthermore, by employing paramagnetic relaxation enhancements an ‘atomic ruler’ was developed that allows for measurement of the immersion depths of lipid carbon atoms. WaaG is a membrane-associated protein that adopts a GT-B fold. For proteins of this type, it has been speculated that the N-terminal domain anchors tightly to the membrane via electrostatic interactions, while the anchoring of the C-terminal domain is weaker. Here, this model was tested for WaaG. It was found by a set of circular dichroism, fluorescence, and NMR techniques that an anchoring segment located in the N-terminal domain termed MIR-WaaG binds electrostatically to membranes, and the structure and localization of isolated MIR-WaaG inside micelles was determined. Full-length WaaG was also found to bind membranes electrostatically. It senses the surface charge density of the membrane whilst not discriminating between anionic lipid species. Motion of the C-terminal domain could not be observed under the experimental conditions used here. Lastly, the affinity of WaaG to membranes is lower than expected, indicating that WaaG should not be classified as a monotopic membrane protein but rather as a peripheral one.

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Manuscript.

APA, Harvard, Vancouver, ISO, and other styles

30

Morandi, Mattia. "Disruption of model membranes' phase behavior upon interaction with hydrophilic/hydrophobic molecules." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAE041/document.

Full text

Abstract:

Ce travail concerne l’altération du comportement de phase de membranes lipidiques lors de leur interaction avec des molécules hydrophiles ou hydrophobes. L’utilisation de sondes moléculaires de fluorescence sensibles à leur micro-environnement constitue un aspect majeur de ce travail. Les techniques de spectroscopie de fluorescence et de microscopie confocale ont été mises à profit pour l’étude du comportement de ces sondes, donnant accès au degré de compacité et d’ordre dans les membranes.Nos résultats montrent que le polystyrène, un plastique rencontré de façon commune dans les régions polluées des océans, présente la capacité de modifier le comportement de phase des membranes lipidiques, entrant notamment en compétition avec le cholestérol.Nous avons montré que la présence élevée de sucres, tel que l’on peut le rencontrer dans certaines situations relevant de la bio-préservation, a pour effet de rompre la qualité de compaction des lipides, et nous avons proposé un nouveau modèle thermodynamique pour interpréter nos résultats.Enfin, les effets sur la membrane de l’incorporation d’un polymère amphiphile comportant un cholestérol greffé ont été étudiés, dans le cadre de l’élaboration de nouvelles stratégies thérapeutiques à base de lipides
This work focuses on the alterations of lipid membrane phase behavior upon interaction with hydrophobic and hydophilic molecules. One major aspect of this thesis is the employement of environment sensitive probes to obtain information on the lipid bilayer packing by means of confocal spectral imaging and fluorescence spectroscopy. Our results show that polystyrene, a commonly found plastic in ocean wastes, has the ability to disrupt the lipid bilayer phase behavior and has a competitive interaction with cholesterol. The presence of high concentration of sugars, relevant in the field of biopreservation, has been found to alter the lipid bilayer packing and a new thermodynamics model has been proposed to complement the experimental results. Finally, the effects of an amphiphilic cholesterol-grafted polymer on model membrane was investigated, providing insight into potential new lipid therapeutic strategies

APA, Harvard, Vancouver, ISO, and other styles

31

Mohaibes, Raheem J. "Efficacy and mechanism of action of novel synthetic fatty acids derivatives in a transgenic Drosophila melanogaster Model of a Alzheimer's disease." Doctoral thesis, Universitat de les Illes Balears, 2015. http://hdl.handle.net/10803/378038.

Full text

Abstract:

- Introducció Alzheimer's disease (AD) is a neurodegenerative disorder characterized by early synaptic and late neuronal loss, affecting more than 26 million people worldwide. Among patients affected with dementia, more than half suffer from Alzheimer’s disease. The biggest risk factor for developing Alzheimer's disease is age. β-amyloid (Aβ) plaques and neurofibrillary p-Tau tangles accumulates in the brains of elderly patients playing a central role in the pathogenesis of AD. During the last years the fruit fly, Drosophila melanogaster has increasingly been used as a model for neurodegenerative disease. Although the adult fly has a simpler nervous system than those of vertebrates, it is capable of higher-order brain functions, including aversive and appetitive learning, and recalling learned information from prior experiences. - Contingut de la investigació This work has been focused on modeling Alzheimer's Disease in Drosophila by expressing two human genes associated with AD (Aβ42 and Tau) in the fly central nervous system. This model displays AD-like neuropathological as well as behavioral symptoms. The main goal of developing such a model is to analyse and study the effect of new synthetic fatty acids molecules in the pathogenesis of AD. Additionally, the model organisms established in this study could provide tools that help to understand disease-specific processes resulting in neuronal loss. This study argues that Drosophila can be used to study the behavioural basis of human neurodegenerative diseases and may provide a model to identify novel therapeutic avenues for neurodegenerative diseases as Alzheimer’s disease. In this work also was studied the effect of membrane lipid therapy on cognitive decline of a transgenic model of Drosophila. This model overexpresses the human amyloid peptide of 42 amino acids (Aβ42), and human Tau protein that play a key role in the development of this disease. - Conclusió The treatment has been based on the use of DHA and its hydroxylated derivate OHDHA, ARA and its hydroxylated form OHARA and EPA and its hydroxylated form OHEPA at 1, 3, 10, 30, 100 and 250 μg/ml of standard food. After testing the transgenes expression in the F1 generation by PCR analysis and Western blot it was evaluated the toxicity of the compounds, and it was demonstrated that food supplementation with OHDHA, OHARA, OHEPA partially restored the loss of locomotor activity and increased the life-span of the flies expressing the human transgenes whereas the DHA, ARA, EPA, form had not significant effects. It has been observed that the concentrations of 30 and 100 μg/ml of hydroxylated form, including the mixtures of (OHDHA+OHARA), (OHEPA+OHARA), and 30 μg/ml of TGMs, LP183A1, LP183A2, was used, have led to cognitive improvement and have maintained or increased the lifespan with respect to the control group. In addition it was analyzed the lipid content from Drosophila heads by using gas chromatography and it was found that the food supplementation with either hydroxylated or non-hydroxylated compounds induced changes in the fatty acid profile of Drosophila. Furthermore it was discovered that the amount of short chain fatty acids (SCFA), from the heads of F1 treated with ARA, EPA and DHA was less than that from untreated F1 flies. Concerning the hydroxylated fatty acids, the reduction in the levels of short chain fatty acid (SCFA) was similar to that of the non-hydroxylated fatty acids. All food supplement tested induced an increase of long chain fatty acids (≥ 18C). ARA, EPA and DHA were present in the fatty acid profile of flies treated with the respective non-hydroxylated food supplements. This fact proves the absorption and incorporation of dietary PUFAs into the Drosophila body tissues.
- Introducció La enfermedad de Alzheimer (AD, del inglés Alzheimer's disease) es una patología neurodegenerativa caracterizada por una pérdida temprana de conexiones sinápticas y, de manera tardía, de neuronas. Esta enfermedad afecta a unos 40 millones de personas en todo el mundo. Entre las personas con demencia, más de la mitad sufren AD. El mayor riesgo para desarrollar la enfermedad de Alzheimer es la edad. De hecho, las placas β-amiloide (Aβ) y ovillos neurofibrilares de fosfo-Tau se acumulan en los cerebros de pacientes ancianos, jugando un papel central en la patogénesis de AD. Además, se han encontrado reducciones significativas en los niveles de los lípidos fosfatidiletanolamina y ácido docosahexaenoico (DHA) en el cerebro de pacientes con AD. Durante la última década, la mosca de la fruta (Drosophila melanogaster) se ha utilizado como modelo para enfermedades neurodegenerativas, debido a que puede ser utilizada para el análisis de conductas como el aprendizaje aversivo y apetitivo, así como su capacidad de utilizar la información aprendida de previas experiencias, aunque la mosca adulta presenta un sistema nervioso mucho más simple que el de vertebrados. - Contingut de la investigació La presente investigación se centra en la utilización de Drosophila como modelo de AD mediante la sobreexpresión de los genes humanos asociados con AD (Aβ42 y Tau) en el sistema nervioso central de la mosca. El principal objetivo de desarrollar este modelo es analizar y estudiar el efecto de ácidos grasos sintéticos novedosos en la terapia de la AD. Conjuntamente, los organismos modelo establecidos en este trabajo pueden constituir un sistema que permita la comprensión de los procesos específicos de la enfermedad que desencadena la pérdida neuronal. Con todo ello, el presente trabajo demuestra que se puede usar Drosophila para estudiar las bases comportamentales de las enfermedades humanas neurodegenerativas y puede suponer un modelo para identificar nuevas terapias para dichas enfermedades, tales como AD. Además, se ha estudiado el efecto de la terapia lipídica de membrana en el declive cognitivo del modelo transgénico de AD de Drosophila. - Conclusió Los tratamientos empleados se basan en el uso de DHA y su derivado hidroxilado OHDHA, ARA y su forma hidroxilada OHARA y EPA y su forma hidroxilada OHEPA, así como derivados de triacilgliceroles (triacilglicerol miméticos, TGM) a dosis crecientes y añadidos en la comida. Tras confirmar la expresión de los transgenes en la generación F1 de las moscas por PCR y western blot, se analizó la toxicidad de los distintos compuestos y se demostró que la suplementación de comida con OHDHA, OHARA, OHEPA restauró la pérdida de actividad locomotora, parcialmente, además, aumentó la vida media de las moscas expresando los transgenes humanos, mientras que DHA, ARA, EPA no presentaron efectos significativos. Se observó que las concentraciones de 30 y 100 μg/ml de las formas hidroxiladas, incluyendo las mezclas de (OHDHA+OHARA), (OHEPA+OHARA) y 30 μg/ml de TGMs, LP183A1, LP183A2, mejoraron la capacidad cognitiva y aumentaron la vida media con respecto al grupo control no tratado. También se analizó el contenido lipídico en membranas de la cabeza de moscas mediante cromatografía de gases y se observó que la suplementación de la comida, tanto con los compuestos hidroxilados como los no-hidroxilados estudiados, indujo cambios en el perfil de ácidos grasos de Drosophila melanogaster. Entre ellos, se observó una menor cantidad de ácidos grasos de cadena corta en cabezas de moscas F1 tratadas con ARA, EPA and DHA en comparación con moscas no tratadas. En cuanto a los ácidos grasos hidroxilados, presentaron un nivel similar en la reducción de los niveles de ácidos grasos de cadena corta. Además, todos los suplementos añadidos a la comida indujeron un aumento de los ácidos grasos de cadena larga (≥ 18C). Finalmente, se observó la presencia de ARA, EPA y DHA en el perfil de ácidos grasos de las moscas tratadas con el correspondiente ácido graso no-hidroxilado. Este hecho prueba la absorción e incorporación de los ácidos grasos poliinsaturados presentes en la dieta en los tejidos de la Drosophila.

APA, Harvard, Vancouver, ISO, and other styles

32

Dannehl, Claudia. "Fragments of the human antimicrobial LL-37 and their interaction with model membranes." Phd thesis, Universität Potsdam, 2013. http://opus.kobv.de/ubp/volltexte/2013/6814/.

Full text

Abstract:

A detailed description of the characteristics of antimicrobial peptides (AMPs) is highly demanded, since the resistance against traditional antibiotics is an emerging problem in medicine. They are part of the innate immune system in every organism, and they are very efficient in the protection against bacteria, viruses, fungi and even cancer cells. Their advantage is that their target is the cell membrane, in contrast to antibiotics which disturb the metabolism of the respective cell type. This allows AMPs to be more active and faster. The lack of an efficient therapy for some cancer types and the evolvement of resistance against existing antitumor agents make AMPs promising in cancer therapy besides being an alternative to traditional antibiotics. The aim of this work was the physical-chemical characterization of two fragments of LL-37, a human antimicrobial peptide from the cathelicidin family. The fragments LL-32 and LL-20 exhibited contrary behavior in biological experiments concerning their activity against bacterial cells, human cells and human cancer cells. LL-32 had even a higher activity than LL-37, while LL-20 had almost no effect. The interaction of the two fragments with model membranes was systematically studied in this work to understand their mode of action. Planar lipid films were mainly applied as model systems in combination with IR-spectroscopy and X-ray scattering methods. Circular Dichroism spectroscopy in bulk systems completed the results. In the first approach, the structure of the peptides was determined in aqueous solution and compared to the structure of the peptides at the air/water interface. In bulk, both peptides are in an unstructured conformation. Adsorbed and confined to at the air-water interface, the peptides differ drastically in their surface activity as well as in the secondary structure. While LL-32 transforms into an α-helix lying flat at the water surface, LL-20 stays partly unstructured. This is in good agreement with the high antimicrobial activity of LL-32. In the second approach, experiments with lipid monolayers as biomimetic models for the cell membrane were performed. It could be shown that the peptides fluidize condensed monolayers of negatively charged DPPG which can be related to the thinning of a bacterial cell membrane. An interaction of the peptides with zwitterionic PCs, as models for mammalian cells, was not clearly observed, even though LL-32 is haemolytic. In the third approach, the lipid monolayers were more adapted to the composition of human erythrocyte membranes by incorporating sphingomyelin (SM) into the PC monolayers. Physical-chemical properties of the lipid films were determined and the influence of the peptides on them was studied. It could be shown that the interaction of the more active LL-32 is strongly increased for heterogeneous lipid films containing both gel and fluid phases, while the interaction of LL-20 with the monolayers was unaffected. The results indicate an interaction of LL-32 with the membrane in a detergent-like way. Additionally, the modelling of the peptide interaction with cancer cells was performed by incorporating some negatively charged lipids into the PC/SM monolayers, but the increased charge had no effect on the interaction of LL-32. It was concluded, that the high anti-cancer activity of the peptide originates from the changed fluidity of cell membrane rather than from the increased surface charge. Furthermore, similarities to the physical-chemical properties of melittin, an AMP from the bee venom, were demonstrated.
Aufgrund der steigenden Resistenzen von Zellstämmen gegen traditionelle Therapeutika sind alternative medizinische Behandlungsmöglichkeiten für bakterielle Infektionen und Krebs stark gefragt. Antimikrobielle Peptide (AMPs) sind Bestandteil der unspezifischen Immunabwehr und kommen in jedem Organismus vor. AMPs lagern sich von außen an die Zellmembran an und zerstören ihre Integrität. Das macht sie effizient und vor allem schnell in der Wirkung gegen Bakterien, Viren, Pilzen und sogar Krebszellen. Das Ziel dieser Arbeit lag in der physikalisch-chemischen Charakterisierung zweier Peptidfragmente die unterschiedliche biologische Aktivität aufweisen. Die Peptide LL-32 und LL-20 waren Teile des humanen LL-37 aus der Kathelizidin-Familie. LL-32 wies eine stärke Aktivität als das Mutterpeptid auf, während LL-20 kaum aktiv gegen die verschiedenen Zelltypen war. In dieser Arbeit wurde die Wechselwirkung der Peptide mit Zellmembranen systematisch anhand von zweidimensionalen Modellmembranen in dieser Arbeit untersucht. Dafür wurden Filmwaagenmessungen mit IR-spektroskopischen und Röntgenstreumethoden gekoppelt. Circulardichroismus-Spektroskopie im Volumen komplementierte die Ergebnisse. In der ersten Näherung wurde die Struktur der Peptide in Lösung mit der Struktur an der Wasser/Luft-Grenzfläche verglichen. In wässriger Lösung sind beide Peptidfragmente unstrukturiert, nehmen jedoch eine α-helikale Sekundärstruktur an, wenn sie an die Wasser/Luft-Grenzfläche adsorbiert sind. Das biologisch unwirksamere LL-20 bleibt dabei teilweise ungeordnet. Das steht im Zusammenhang mit einer geringeren Grenzflächenaktivität des Peptids. In der Zweiten Näherung wurden Versuche mit Lipidmonoschichten als biomimetisches Modell für die Wechselwirkung mit der Zellmembran durchgeführt. Es konnte gezeigt werden, dass sich die Peptide fluidisierend auf negativ geladene Dipalmitylphosphatidylglycerol (DPPG) Monoschichten auswirken, was einer Membranverdünnung an Bakterienzellen entspricht. Eine Interaktion der Peptide mit zwitterionischem Phosphatidylcholin (PC), das als Modell für Säugetierzellen verwendet wurde, konnte nicht klar beobachtet werden, obwohl biologische Experimente das hämolytische Verhalten zumindest von LL-32 zeigten. In der dritten Näherung wurde das Membranmodell näher an die Membran von humanen Erythrozyten angepasst, indem gemischte Monoschichten aus Sphingomyelin (SM) und PC hergestellt wurden. Die physikalisch-chemischen Eigenschaften der Lipidfilme wurden zunächst ausgearbeitet und anschließend der Einfluss der Peptide untersucht. Es konnte anhand verschiedener Versuche gezeigt werden, dass die Wechselwirkung von LL-32 mit der Modellmembran verstärkt ist, wenn eine Koexistenz von fluiden und Gelphasen auftritt. Zusätzlich wurde die Wechselwirkung der Peptide mit der Membran von Krebszellen imitiert, indem ein geringer Anteil negativ geladener Lipide in die Monoschicht eingebaut wurde. Das hatte allerdings keinen nachweislichen Effekt, so dass geschlussfolgert werden konnte, dass die hohe Aktivität von LL-32 gegen Krebszellen ihren Grund in der veränderten Fluidität der Membran hat und nicht in der veränderten Oberflächenladung. Darüber hinaus wurden Ähnlichkeiten zu Melittin, einem AMP aus dem Bienengift, dargelegt. Die Ergebnisse dieser Arbeit sprechen für einen Detergenzien-artigen Wirkmechanismus des Peptids LL-32 an der Zellmembran.

APA, Harvard, Vancouver, ISO, and other styles

33

CANEPA, ESTER. "Nonspecific Interactions of Amphiphilic Nanoparticles and Biomimetic Membranes." Doctoral thesis, Università degli studi di Genova, 2021. http://hdl.handle.net/11567/1046376.

Full text

Abstract:

Robust control over nanoparticle (NP)-cell interactions is essential to the rational design of safe, advanced, and tailored nano-bio technologies. Achieving control over NP behavior at the cellular interface relies on the fundamental need to elucidate the physicochemical principles underlying the interactions between NPs and cell membranes. Despite numerous research efforts, the propensity of surface-modified NPs to interfere (or not) with the organization and function of cell membranes is still far from clear due to the inherently complex and dynamic nature of these biological barriers. In this thesis, experimental investigations were undertaken to tackle some aspects of nonspecific NP-membrane interactions that are still unclear or very poorly addressed. Sub-5 nm gold NPs protected by a mixture of hydrophobic and ω-charged hydrophilic thiols were considered. These amphiphilic NPs possess high biomedical potential as they are able to passively enter living cells for theranostic purposes. Based on a biomimetic approach, lipid bilayers of varying structural and morphological complexity were employed to model the lipid structure of cell membranes. This work revealed that the sign of the NP surface charge is not responsible for different NP behavior in the interaction with neutral membranes. Notably, anionic and cationic NPs were shown not to damage the membrane integrity during passive bilayer penetration. Furthermore, anionic NPs were revealed to perturb the lateral lipid phase separation of multidomain membranes in a concentration-dependent manner and form peculiar bilayer-embedded ordered aggregates. Finally, the cholesterol-tuned reduction in bilayer fluidity was disclosed to dramatically hinder passive NP uptake into fluid membranes. Taken together, these findings provide a novel contribution in elucidating how amphiphilic entities endowed with surface conformational flexibility, such as ligand-protected NPs, can interact with cell membranes.

APA, Harvard, Vancouver, ISO, and other styles

34

Veatch, Sarah Louise. "Liquid immiscibility in model bilayer lipid membranes /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/9772.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

Valet, Manon. "Transport properties in biomimetic tissues." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS397.

Full text

Abstract:

Dans ce travail nous développons un modèle expérimental biomimétique de la communication cellule-cellule. Il s'agit de réseaux de gouttelettes aqueuses baignant dans l'huile et reliées par des bicouches lipidiques ornées de canaux ioniques. Pour produire ces réseaux de gouttelettes, nous développons d'abord une méthode d'impression originale basée sur l'extraction périodique à travers une interface huile/air d'un capillaire dans lequel la phase aqueuse est injectée. Nous incorporons ensuite aux bicouches un canal ionique – l’hémolysine - pour étudier la diffusion d'une sonde fluorescente dans des réseaux nanoporeux 1D par microscopie d’épifluorescence. Nous établissons que le temps de diffusion caractéristique dépend de façon non linéaire de la concentration introduite en nanopores. Nous montrons que nos résultats peuvent être compris par le biais d’une description théorique basée sur les temps de premier passage, dans laquelle les nanopores sont regroupés dans la membrane plutôt qu'isolés. Dans la dernière partie, nous utilisons des réactions cell-free pour exprimer directement dans les gouttelettes l'hémolysine précédemment utilisée ou le canal ionique mécanosensible MscL. Nous avons démontré dans ce cadre l'insertion et la fonctionnalité de l'hémolysine ainsi synthétisée par microscopie confocale et mesures électrophysiologiques. Ces résultats permettront d’entreprendre l'étude des propriétés de transport diffusives dans les réseaux mécanosensibles sous contrainte mécanique
In this thesis work, we develop an experimental model biomimetic of cell-cell communication. It consists in networks of aqueous droplets bathing in oil and connected by lipid bilayers decorated with ion channels. To produce these droplet networks, we first develop an original printing method based on the periodic extraction through an oil/air interface of a capillary in which the aqueous phase is injected. When the bilayers are decorated with the ion channel hemolysin, we then study the diffusion of a fluorescent probe in 1D nanoporous networks, using epifluorescence microscopy. We establish that the characteristic diffusion time depends non-linearly on the nanopores concentration. We show that our results are well captured within a first passage time theoretical description, in which nanopores are clustered rather than being independent. In the last part, we use cell-free reactions to express directly within the droplets the previously used hemolysin or the mechanosensitive ion channel MscL. We successfully demonstrate the insertion and functionality of synthesized hemolysin using both confocal microscopy and electrophysiological measurements. These results pave the way to the study of diffusive transport properties in mechanosensitive networks under mechanical stress

APA, Harvard, Vancouver, ISO, and other styles

36

Nomura, Daniela Akiko. "Caracterização estrutural de dispersões aquosas de lipídios aniônicos." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-08052018-005348/.

Full text

Abstract:

É conhecido que a força iônica do meio desempenha um papel fundamental na estrutura de vesículas aniônicas de DMPG (dimiristoil fosfatidilglicerol) em dispersões aquosas. A baixa força iônica (~ 6 mM), as dispersões de DMPG exibem várias características anômalas, que foram interpretadas como a abertura de poros na bicamada ao longo da larga região de transição de fase gel-fluida (de ~ 18°C a 30°C). Aqui, revisitamos o sistema de DMPG em tampão a baixa força iônica, mas com dispersões obtidas após a extrusão por filtros de 100 nm, portanto menos polidispersas. Para enfatizar as interações eletrostáticas entre as cabeças polares dos lipídios, que não estarão blindadas pela presença de sais na solução, estudamos dispersões de DMPG em água pura, de modo a monitorar os agregados presentes na dispersão, e suas interações. As dispersões em água foram caracterizadas antes e depois da extrusão. Para tal, utilizamos diversas técnicas experimentais, em diferentes temperaturas: espalhamento de luz estático (SLS) e dinâmico (DLS), calorimetria diferencial de varredura (DSC), Ressonância Paramagnética Eletrônica (RPE) de marcadores de spin incorporados aos agregados, espalhamento de raios-X a altos e baixos ângulos (WAXS e SAXS), e medidas de viscosidade, turbidez, mobilidade eletroforética e condutividade elétrica. Resultados das várias técnicas com dispersões extrusadas de DMPG em tampão mostraram que o comportamento anômalo é observado de forma similar ao de dispersões não extrusadas. Entretanto, o pico de SAXS em muito baixo ângulo é visto de 5 a 45°C, e não apenas na região de transição de fase, portanto não deve ser modelado como a distância entre poros na bicamada lipídica que se abririam nesta região. A distância de repetição relacionada a este pico diminui na região de transição de fase, e com o aumento da concentração lipídica. Medidas de DSC indicaram que, em água, a região de transição de fase da vesícula de DMPG é ainda mais ampla, começando em torno de 10°C, mas ainda terminando em ~ 30oC. No entanto, a alta condutividade elétrica, viscosidade, mobilidade eletroforética, raio efetivo, e a baixa turbidez, vistas apenas na região de transição de fase do DMPG em tampão, são encontradas até altas temperaturas em água, quando a bicamada lipídica já se encontra na fase fluida. Medidas de RPE e WAXS mostraram a transição da membrana de uma fase mais rígida/imóvel/organizada para uma fase mais frouxa/móvel. Dados de espalhamento de luz, RPE e SAXS mostram que, similar ao DMPG em tampão, em água, o DMPG organiza-se como vesículas esféricas, unilamelares, mas possivelmente menores e mais carregadas, exibindo fortes interações vesícula-vesícula. Nas medidas de SAXS, o pico de Bragg na região de muito baixo ângulo foi visto em todas as temperaturas (de 5 a 60°C), sendo que a distância de repetição diminui para temperaturas maiores do que 10oC. Os resultados obtidos para dispersões em água, reforçam o comportamento anômalo observado anteriormente para dispersões em tampão em baixa força iônica. De acordo com eles, propomos a existência de vesículas altamente deformadas e ionizadas a partir de uma certa temperatura, T1 para o DMPG em água e Tmon em tampão baixa força iônica, sendo que em água a forte repulsão eletrostática PG--PG- levaria a fortes deformações e interações vesícula-vesícula, em uma ampla extensão de temperaturas.
It is known that the ionic strength plays a fundamental role in the structure of DMPG (dimyristoyl phosphatidylglycerol) anionic vesicles in water medium. At low ionic strength (~ 6 mM), DMPG dispersions display several anomalous characteristics, which were interpreted as the opening of bilayer pores along the wide bilayer gel-fluid transition region (from ~ 18°C to 30°C). Here, we revisit DMPG in buffer at low ionic strength, but with dispersions obtained after the extrusion by 100 nm filters, thus less polydisperse. To emphasize electrostatic interactions between the polar head-groups, which will not be shielded by ions in solution, we studied DMPG dispersions in pure water to monitor the aggregates in the dispersion and their interactions. Water dispersions were characterized before and after extrusion. For such, we used several experimental techniques, at different temperatures: light scattering, both static (SLS) and dynamic (DLS); differential scanning calorimetry (DSC); electron spin resonance (ESR) of spin labels incorporated into the aggregates, Small and Wide Angle X-Ray Scattering (SAXS and WAXS); and viscosity, turbidity, electrophoretic mobility and electrical conductivity measurements. Several techniques with extruded dispersions of DMPG in buffer showed that the anomalous behavior is also observed. However, the SAXS peak at very low angles is seen from 5 to 45°C, and not only in the phase transition region, therefore it should not be modeled as the distance of correlated pores in the lipid bilayer that would open in this region. The repeating distance related to this peak decreases in the phase transition region, and with increasing lipid concentration. DSC indicates that, in water, the bilayer gel-fluid transition is even wider, starting around 10oC but still ending ~ 30oC. However, high electric conductivity, viscosity, electrophoretic mobility, effective radius and low turbidity found only in the gel-fluid transition region for DMPG in buffer, are found at higher temperatures in water, when lipid bilayers are already in the fluid state. ESR and WAXS measurements evidenced the transition of the membrane from a more rigid/immobile/organized phase to a more soft/mobile phase. Light scattering, ESR and SAXS data showed that, similar to DMPG in buffer, in water, DMPG is organized as spherical unillamelar vesicles, but possibly smaller, highly charged, displaying strong vesicle-vesicle interactions. With SAXS the Bragg peak at very low angles was seen at all temperatures (from 5 to 60°C) with the repetition distance decreasing at temperatures higher than 10 ° C. The results obtained for water dispersions reinforce the anomalous behavior previously observed for buffer at low ionic strength dispersions. According to them, we propose the existence of highly deformed and ionized vesicles from a certain temperature, T1 for DMPG in water and Tmon in buffer at low ionic strength. In water the strong PG- - PG- electrostatic repulsion would lead to strong deformations and vesicle-vesicle interactions, over a wide range of temperatures.

APA, Harvard, Vancouver, ISO, and other styles

37

Barrett, Matthew. "Structure and dynamics of model lipid membranes." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17540.

Full text

Abstract:

Das Peptid Amyloid-beta wird seit vielen Jahren mit der Alzheimer''schen Demenz in Verbindung gebracht, aber die Verbindung zwischen dem Peptid und der Herkunft der Symptome bleibt unklar. Eine neue Hypothese besagt, dass Wechselwirkungen von Mono- oder Oligomeren des Amyloid-beta mit neuronalen Zellmembranen zu Veränderungen der Membran-Doppelschichtsruktur führen und Störungen dynamischer Prozesse in den Membranen verursachen können. Mit Methoden der Röntgen- und Neutronenstreuung wurden die Struktur und Dynamik von Modellmembranen und Änderungen durch den Einfluss des Peptids Amyloid-beta auf die Modellmembranen untersucht. Es konnte gezeigt werden, dass Monomere des Peptidfragments Amyloid-beta 22-40 in anionische Lipidmembranen eingebaut werden. Mittels quasielastischer-inkohärenter Neutronenstreuung wurde die Dynamik von Lipidmembran untersucht. Ein Anteil von 1,5 mol % Amyloid-beta 22-40 in einer Lipidmembran bei 30°C verursacht eine Verringerung der Diffusionskoeffizienten sowohl der Schwerpunktbewegung der Lipide im ns-Bereich als auch der Dynamik der Fettsäurereste im ps-Bereich. Andererseits wird in der Gelphase der Lipidmembran bei 15°C ein Anstieg der Diffusionskoeffizienten beider Prozesse beobachtet. Eine Serie von Lipidproben mit unterschiedlichem Cholesteringehalt und eingelagerten Peptiden Amyloid-beta 1-42 und Amyloid-beta 22-40 wurde Mittels Röntgendiffraktion charakterisiert. Für das Peptid Amyloid-beta 22-40 wurden zwei Positionen gefunden, eine auf der Oberfläche der Membran, eine zweite in der Membran eingelagert. Das Peptid Amyloid-beta 1-42 ist teilweise in die Membran eingelagert und ist in einer 40 mol % Cholesteringehaltige Membrane durch eine einzelne Position modelliert. Zusätzlich wird der Entwurf und die Inbetriebnahme der BerILL Feuchtekammer beschrieben.
The peptide amyloid-beta has long been associated with Alzheimer’s disease; however the link between the peptide and the origin of symptoms is poorly understood. An emerging hypothesis is that monomeric and oligomeric forms of the peptide interact with neuronal membranes, resulting in perturbations in the bilayer structure and in the dynamic processes which take place in the bilayer. Using X-ray and neutron scattering techniques, the structure and dynamics of model lipid membranes and the changes which arise in the presence of amyloid-beta peptide fragments have been studied. Monomers of the peptide fragment amyloid-beta 22-40 were found to intercalate into an anionic lipid bilayer. Through quasi-elastic neutron scattering, dynamics of bilayer lipids were observed. The presence of 1.5 mol % of the peptide results in a decrease in the diffusion coefficients for lipid centre of mass motion on the nanosecond time-scale, as well as for the lipid tail dynamics on the picosecond scale at 30°C. On the other hand, in the gel-phase of the lipid, at 15°C, an increase in the diffusion coefficients for both of these processes was observed. A series of samples with various cholesterol content and either the amyloid-beta 22-40 peptide fragment or the amyloid-beta 1-42 full length peptide was characterized using X-ray diffraction. The amyloid-beta 22-40 peptide was found to populate two positions, on the surface and embedded in the bilayer. The amyloid-beta 1-42 peptide embeds itself into the membrane, and is modelled by a single population for high cholesterol levels (40 mol % cholesterol). In addition, the design and commissioning of the BerILL humidity chamber, a sample environment with precise temperature and humidity control compatible with neutron scattering experiments is presented.

APA, Harvard, Vancouver, ISO, and other styles

38

Azouz, Mehdi. "Alzheimer's disease neurotoxic peptides : towards a comprehension of their modes of action on model membranes." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0419.

Full text

Abstract:

La maladie d'Alzheimer (MA) est une neuropathologie complexe qui constitue la principale forme de démence chez l'être humain. Étroitement associée au vieillissement, elle se manifeste par une perte progressive de la mémoire et des fonctions cognitives. Avec 30 millions d’individus concernés au niveau mondial et des estimations voyant ce chiffre quadrupler d'ici 2050, elle constitue aujourd’hui une menace sociétale majeure. L’atrophie cérébrale observée chez les patients atteints de la MA est la conséquence d’un long processus de neurodégénérescence qui intervient au niveau moléculaire et s’amorce bien avant l’apparition des symptômes. Deux marqueurs histopathologiques ont été identifiés comme étant associés à ce processus : les plaques séniles, composées du peptide Abêta et les dégénérescences neurofibrillaires constituées de la protéine Tau. Ces deux molécules, considérées comme les protagonistes décisifs du développement de la MA, concentrent les recherches afin de mieux comprendre leurs rôles dans le processus neurodégénératif et pouvoir mettre en place des solutions thérapeutiques, inexistantes à ce jour.Un des axes de recherche majeurs se focalise sur l’interaction de ces peptides avec la membrane plasmique. L’occurrence d’un tel phénomène pourrait potentiellement être en cause dans la mort neuronale s’il s’avérait délétère. Il est donc capital d’étudier en détail ces processus afin d’identifier les facteurs qui pourraient conduire Abêta et Tau à endommager l’intégrité des membranes. De nombreux travaux ont démontré que certains lipides pouvaient promouvoir ces interactions. Cependant, les conclusions sont parfois divergentes et un consensus commun reste à trouver quant à leurs rôles.Ce travail de thèse s’est consacré à l’étude des modes d’action du peptide Abêta et d’un fragment clé de la protéine Tau, le peptide K18, sur des membranes modèles, en se focalisant principalement sur l’influence de certains lipides. Afin d’élucider les mécanismes qui régissent ces phénomènes, les processus de solubilisation membranaires ont dans un premier temps été étudiés avec des molécules amphiphiles bien caractérisées : les détergents. Cette étude a permis d’établir que les phénomènes de solubilisation membranaires peuvent varier en fonction de la composition membranaire et démontrer de la sélectivité.Le cœur du projet était de visualiser les effets des peptides amyloïdes Abêta et K18 sur des modèles membranaires, les bicouches supportées, avec pour principale technique d’investigation la microscopie à force atomique. Elle nous a permis d’observer ces phénomènes in situ, en conditions physiologiques et à l’échelle sub-micrométrique. Nous avons pu montrer que la composition membranaire était un facteur pouvant moduler l’interaction avec Abêta. L'étude établit que les domaines lipidiques favorisent les perturbations membranaires induites par le peptide. Il est proposé que des défauts d'empilement lipidiques aux interfaces de ces domaines agissent comme des sites d'adsorption du peptide, menant à la destruction des membranes. En utilisant la même approche, avec des compositions lipidiques plus en adéquation avec Tau, nous avons pu établir que K18 induisait également des effets de solubilisation en fonction de la nature des lipides dans la membrane et des propriétés qui leurs sont associées.Dans les deux cas, nous montrons que les effets délétères que peuvent induire ces peptides se manifestent par des effets comparables à ceux des détergents et sont dépendants de la composition des membranes. L’agrégation des peptides, qui peut conduire à leur fibrillation, n’a également été mise en évidence qu’en présence de certains lipides.Ce travail de thèse apporte de nouvelles informations sur le caractère décisif de la membrane à pouvoir moduler les interactions avec les peptides Abêta; et K18. Par extension aux membranes cellulaires, ces phénomènes pourraient potentiellement être associés aux processus neurodégénératifs impliqués dans la MA
Alzheimer’s disease is a complex neuropathological disorder that constitutes the prime form of dementia. Intimately related to ageing, it is associated to the gradual loss of memory and cognitive functions in individual suffering from the pathology. With nearly 30 million people concerned today, and the alarming trends predicting this figure to increase fourfold by 2050, Alzheimer’s disease will constitute a major burden for our societies in the upcoming decades. The cerebral atrophy occurring within the brain results from slow and progressive neurodegenerative mechanisms triggered many years before the appearance of the first symptoms. Two histopathological markers have been identified as strongly associated to the neurodegeneration: the senile plaques, majorly composed of the amyloid peptide Abeta, and the neurofibrillary tangles, constituted of the abnormally phosphorylated form of Tau protein. These two molecules, hence considered as the main culprits of the disease, are therefore under the spotlight of researchers who try to better understand the respective roles in the neurodegeneration process and uncover therapeutic solutions to a still uncurable disease.One of the promising research axis is focusing on the interplay between these molecules and the plasma membrane as potential interactions could convincingly rationalize the neural cell deaths if they happened to be deleterious. Therefore, investigate these interactions in detail is of primary importance to identify the factors that might drive Abeta and Tau to cause damages on membranes. A strong body of evidences has demonstrated that certain lipids could promote these interactions and are then suspected to be involved into detrimental phenomena. However, numerous results appear to be contradicting and consensual conclusions are still lacking.This PhD was dedicated to the investigation of the effects of Abeta and K18, a key peptide fragment of Tau protein, on membranes with a particular focus on the influence of lipids. The aim of this work was to elucidate the action mechanisms of these peptides.To first comprehend how membrane damages can be induced, we first focused on the solubilising ability of extensively used amphiphile agents: detergents. As a first study, we revealed that the membrane composition and the physicochemical properties of lipids play an important role in driving the solubilisation of the bilayer, a process that can even lead to a selectivity during the lipid extraction.The core part of the project was to visualize the effects of the amyloid peptides Abeta and K18 on supported lipid bilayers as membrane models, using atomic force microscopy as an investigation technique. With its high spatial resolution and its ability to operate in physiological milieu, this approach has shown that the membrane composition could promote membrane disruption induced by Abeta oligomers in a lipid-dependent manner. More importantly, we propose that packing defects at the interface of membrane domains act as adsorption and nucleation sites leading to membrane damages.Using the same strategy, we observed that K18 could also induce solubilisation phenomenon and demonstrated to be sensitive to the aspect of lipid order in membranes.In both cases, we highlighted that these peptides could be detrimental to supported lipid bilayers and that their disruptive abilities, associated to detergent-like mechanisms, were intimately dependent of lipids. We also show that the aggregation, a phenomenon that can lead to the peptides fibrillation can only be triggered in presence of certain lipids.This work provides important insights about the decisive role of membrane composition in modulating interactions with the Abeta and K18. This interplay could constitute one of the numerous factors that promote neurotoxic phenomena, taking part in the complex neurodegenerative processes associated to Alzheimer’s disease

APA, Harvard, Vancouver, ISO, and other styles

39

Arouri, Ahmad. "Interaction of antimicrobial peptides with model lipid membranes." kostenfrei, 2009. http://nbn-resolving.de/urn:nbn:de:gbv:3:4-540.

Full text

APA, Harvard, Vancouver, ISO, and other styles

40

Leidy, Chad. "Thermotropic behavior of lipid domains in model membranes /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2002. http://uclibs.org/PID/11984.

Full text

APA, Harvard, Vancouver, ISO, and other styles

41

Brown, Aidan. "A physical study of model biological membranes." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609720.

Full text

APA, Harvard, Vancouver, ISO, and other styles

42

Fuhrer, Andrew B. "The Role of Lipid Domains and Sterol Chemistry in Nanoparticle-Cell Membrane Interactions." Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1596569401131742.

Full text

APA, Harvard, Vancouver, ISO, and other styles

43

Beard, Jason. "A model of integrative feedback and homeostasis in lipid biosynthesis." Thesis, University of Southampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289506.

Full text

APA, Harvard, Vancouver, ISO, and other styles

44

Kluzek, Monika. "Lipid membrane alteration under exposure to alpha-cyclodextrins and pH-responsive pseudopeptide polymers." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAE045/document.

Full text

Abstract:

Le développement de nanotransporteurs basés sur des lipides, des polymères et des nanoparticules avec des propriétés «sur mesure» pour augmenter l’efficacité de médicaments, fait l’objet de recherches intensives. Toutefois, la physico-chimie subtile des intéractions polymères-lipides and nanoparticules-lipides présente encore de larges domaines mal compris et de nombreuses questions sans réponse. Ce projet de recherche doctoral utilise des techniques de visualisation (Cryo-MET, LSCM), et de caractérisation (ITC, DSC, SAXS, SANS, QCM-D) avancées pour obtenir des informations nouvelles sur les mécanismes d’interaction entre des Cyclodextrines-α d’autre part, des polymères sensibles au pH d’autre part, et des bicouches modèle de DOPC. La forte influence de ces deux composés sur ces systèmes modèle élucide certains aspects relatifs à la toxicité vis-à-vis des membranes biologiques et suggère de nouvelles approches pour des applications pharmaceutiques
The primary goal of nanomedicine is to improve clinical outcomes. To this end, the development of nanocarriers based on lipids, polymers and nanoparticles with tailor-made properties that enhance the in vivo potency of drugs is a subject of intense research. However, the subtle physical-chemistry of the polymer-lipid and nanoparticle-lipid interactions still present many poorly understood fields of investigation as well as unanswered questions. This doctoral research project utilizes state-of-the-art visualization (Cryo-TEM, LSCM) and characterization (ITC, DSC, SAXS, SANS, QCM-D) techniques to gain novel insights into the interaction between α-Cyclodextrins in the first hand, a pH-responsive polymer in the other hand, and model DOPC bilayers. The strong influence of both compounds on these model systems elucidate some aspects regarding biological membrane toxicity and suggests novel strategies for pharmaceutical applications

APA, Harvard, Vancouver, ISO, and other styles

45

Helmers, Michael. "Kinks in a model for two-phase lipid bilayer membranes." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:15343985-1b1c-4123-838d-8e157e837db1.

Full text

Abstract:

In the spontaneous curvature model for two-phase lipid bilayer membranes the shape of vesicles is governed by a combination of an elastic bending energy and an interface energy that penalises the size of phase boundaries. Each lipid phase induces a preferred curvature to the membrane surface, and these curvatures as well as phase boundaries may lead to the development of kinks. In a rotationally symmetric setting we introduce a family of energies for smooth surfaces and phase fields for the lipid components and study convergence to a sharp-interface limit, which depends on the choice of the bending parameters of the phase field model. We prove that, if kinks are excluded, our energies $Gamma$-converge to the commonly used sharp-interface spontaneous curvature energy with the additional assumption of $C^1$-regularity across interfaces. For a choice of parameters such that kinks may appear, we obtain a limit that coincides with the $Gamma$-limit on all reasonable membranes and extends the classical model by assigning a bending energy also to kinks. We illustrate the theoretical result by some numerical examples.

APA, Harvard, Vancouver, ISO, and other styles

46

Bingham, Richard John. "A continuum model of the electroporation of bilayer lipid membranes." Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.535113.

Full text

APA, Harvard, Vancouver, ISO, and other styles

47

Yamamoto, Akihisa. "Mesoscopic structural dynamics and mechanics of cell membrane models." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/198928.

Full text

APA, Harvard, Vancouver, ISO, and other styles

48

Fournier, Luc. "A lattice model for the rupture kinetics of lipid bilayer membranes." Thesis, University of Ottawa (Canada), 2002. http://hdl.handle.net/10393/6293.

Full text

Abstract:

We have constructed a model for the kinetics of rupture of membranes under tension, applying physical principles relevant to lipid bilayers held together by hydrophobic interactions. The membrane is characterized by the bulk compressibility (for expansion) K and the thickness 2ht of the hydrophobic part of the bilayer. The model is a lattice model which incorporates stress relaxation, and considers the nucleation of pores at constant area, constant temperature, and constant particle number. The particle number is conserved by allowing multiple occupancy of the sites. A value for the rigidity of the phopholipid tails in the Lalpha liquid phase are found for saturated and unsaturated lipids, and long diblock copolymers. An equilibrium "phase diagram" is constructed as a function of temperature and strain with the pores total surface and distribution as the order parameters. With parameters relevant to saturated phosphatidylcholine (PC) lipid membranes, well defined regions of "no pores", "protopores (non-critical pores)", "rupture" are found. The model also reproduces recent results on super-thick membranes, and on membranes in presence of peptides. Free energy curves as a function of total pore surface are presented for various values of tension and temperature, and the fractal dimension of the pore edge is evaluated.

APA, Harvard, Vancouver, ISO, and other styles

49

Malcolmson, Richard Joseph. "Physical studies of cholesterol and cholesteryl esters in model membranes." Thesis, Edinburgh Napier University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385910.

Full text

APA, Harvard, Vancouver, ISO, and other styles

50

Asghari, Adib Ali. "Interactions of Engineered Silica Nanoparticles with Cell Membrane Models." Ohio University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1501764587639053.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Model lipid membrane'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles