Um die anderen Arten von Veröffentlichungen zu diesem Thema anzuzeigen, folgen Sie diesem Link: Membranes, bilayers and vesicles.
Dissertationen zum Thema „Membranes, bilayers and vesicles“
Geben Sie eine Quelle nach APA, MLA, Chicago, Harvard und anderen Zitierweisen an
Machen Sie sich mit Top-50 Dissertationen für die Forschung zum Thema "Membranes, bilayers and vesicles" bekannt.
Neben jedem Werk im Literaturverzeichnis ist die Option "Zur Bibliographie hinzufügen" verfügbar. Nutzen Sie sie, wird Ihre bibliographische Angabe des gewählten Werkes nach der nötigen Zitierweise (APA, MLA, Harvard, Chicago, Vancouver usw.) automatisch gestaltet.
Sie können auch den vollen Text der wissenschaftlichen Publikation im PDF-Format herunterladen und eine Online-Annotation der Arbeit lesen, wenn die relevanten Parameter in den Metadaten verfügbar sind.
Sehen Sie die Dissertationen für verschiedene Spezialgebieten durch und erstellen Sie Ihre Bibliographie auf korrekte Weise.
1
Bertrand, Martin. „Deformed Soft Matter under Constraints“. Thesis, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/20564.
Der volle Inhalt der QuelleAnnotation:
In the last few decades, an increasing number of physicists specialized in soft matter, including polymers, have turned their attention to biologically relevant materials. The properties of various molecules and fibres, such as DNA, RNA, proteins, and filaments of all sorts, are studied to better understand their behaviours and functions. Self-assembled biological membranes, or lipid bilayers, are also the focus of much attention as many life processes depend on these. Small lipid bilayers vesicles dubbed liposomes are also frequently used in the pharmaceutical and cosmetic industries. In this thesis, work is presented on both the elastic properties of polymers and the response of lipid bilayer vesicles to extrusion in narrow-channels. These two areas of research may seem disconnected but they both concern deformed soft materials. The thesis contains four articles: the first presenting a fundamental study of the entropic elasticity of circular chains; the second, a simple universal description of the effect of sequence on the elasticity of linear polymers such as DNA; the third, a model of the symmetric thermophoretic stretch of a nano-confined polymer; the fourth, a model that predicts the final sizes of vesicles obtained by pressure extrusion. These articles are preceded by an extensive introduction that covers all of the essential concepts and theories necessary to understand the work that has been done.
2
Harman, Alison. „A Molecular Dynamics Simulation of Vesicle Deformation and Rupture in Confined Poiseuille Flow“. Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/26127.
Der volle Inhalt der QuelleAnnotation:
Vesicles are simple structures, but display complex, non-linear dynamics in fluid flow. I investigate the deformation of nanometer-sized vesicles, both fully-inflated and those with excess area, as they travel in tightly confined capillaries. By varying both channel size and flow strength, I simulate vesicles as they transition from steady-state to unstable shapes, and then rupture in strong flow fields. By employing a molecular dynamics model of the vesicle, fluid, and capillary system one is able to rupture the lipid bilayer of these vesicles. This is unique in that most other numerical methods for modelling vesicles are unable to show rupture. The rupture of fully-inflated vesicles is applicable to drug delivery in which the release of the encapsulated medicine needs to be controlled. The deformation and rupture of vesicles with excess area could be applicable to red blood cells which have similar rheological properties.
3
Blochel, Andreas. „Adsorption of halogenated phenolate ions to egg-phosphatidylcholine vesicles“. PDXScholar, 1992. https://pdxscholar.library.pdx.edu/open_access_etds/4271.
Der volle Inhalt der Quelle
4
Kuhlmann, Jan Wilhelm. „Modulation of lateral membrane tension and SNARE-mediated single vesicle fusion on pore spanning membranes“. Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2017. http://hdl.handle.net/11858/00-1735-0000-0023-3F13-E.
Der volle Inhalt der Quelle
5
Norman, Robert Ellis. „Statistical mechanics of vesicles, membranes and interfaces“. Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358818.
Der volle Inhalt der Quelle
6
Lee, Lester Y. C. „Transmembrane electron transfer in artificial bilayers /“. Full text open access at:, 1985. http://content.ohsu.edu/u?/etd,86.
Der volle Inhalt der Quelle
7
Robinson, Alan Jonathan. „The computer simulation of lipid bilayers and biological membranes“. Thesis, University of Oxford, 1996. https://ora.ox.ac.uk/objects/uuid:787e13b4-4a3e-44ce-bd2d-9bb847631a5d.
Der volle Inhalt der QuelleAnnotation:
Computer simulations of lipid bilayers and biological membranes using molecular mechanics calculations have been undertaken in order to study these complex systems which are so vital in the control and functioning of many biological processes. The preliminary research involved the development of a model that recreates experimentally observed properties. This is not a trivial task since structural data on lipids in the biologically relevant liquid crystalline phase are unavailable precisely because of their fluid nature. The starting configuration designed for simulation of lipids in the fluid phase contained four different lipid conformations. These reflected the most probable head group and glycerol moiety conformations plus gauche dihedrals were introduced into the hydrocarbon chains so that they resembled chains in the fluid phase and reduced the time required for equilibration molecular dynamics. The bilayer model was then used to study cholesterol-lipid and peptide-lipid interactions. The cholesterol simulations illustrated how this molecule orders lipid chains by virtue of its rigid skeleton while the peptide simulations showed how cooperative the interactions between proteins and lipids are. Finally simulations of ion channels of gramicidin and melittin in membranes were accomplished and conclusions drawn on the nature and mechanism of the toxicity of melittin and of how water and ion translocation occurs along gramicidin channels.
8
Maleki, Karyak Mohsen. „Modeling and analysis of lipid bilayers with applications to vesicles and lipoprotein particles“. Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=121455.
Der volle Inhalt der QuelleAnnotation:
Continuum approaches for modeling lipid bilayers are developed and applied to two-phase lipid vesicles and discoidal high-density lipoprotein (HDL) particles. First, relying on a three-dimensional model, the mechanics of a lipid bilayer with spontaneous curvature is considered. Kinematics, material symmetry, stress relations, and coherency of lipid bilayer leaflets are discussed. Treating a lipid bilayer as a thin structure, the areal energy density of a lipid bilayer with spontaneous curvature is obtained using a dimension-reduction procedure. Attention is paid on the source of spontaneous curvature in the well known Canham–Helfrich energy density. Also, the effect of constitutive asymmetry of the leaflets on the areal energy density of a lipid bilayer is highlighted.Considering a two-phase vesicle as system of coexisting spherical domains, its equilibrium is studied using a simple continuum model. Multidomain and ground-state configurations are considered. Whereas in the former case multiple budded lipid domains coexist on a vesicle, in the latter case the vesicle is composed of two large lipid domains. Variations of the net potential-energy of a multidomain vesicle with the number of lipid domains and osmotic pressure are studied. Based on an energy comparison argument, two ground-state configurations corresponding to minimum energy levels are identified: pinched-off and complete sphere configurations. The results indicate that osmotic pressure and initial excess radius play key roles in the final shape of attaining ground-state configurations. The critical values of these parameters are identified. Lastly, the equilibrium and stability of a discoidal HDL particle are studied. A model in which the lipid bilayer and double-belt apoA-I components of discoidal HDL particle are represented by a material surface and a material curve perfectly bonded to the edge of the surface is proposed. The curvature energy and surface tension of lipid bilayer and the bending energy of apoA-I chain are included. Adopting a variational scheme, nonlinear equilibrium equations of a discoidal HDL particle in a general configuration are derived using both direct, geometrically-based and parametrized formulations. The linearized equilibrium equations of a flat circular HDL particle are obtained and its linear stability is investigated using the second variation method. An energy comparison method is applied and is found to offer a handy approach for ascertaining linear stability. Numerical results are provided for the equilibrium and stability of flat circular HDL particle. A stability plane indicating different stable and unstable regions of underlying dimensionless input parameters is provided. Possible pathways of stability change and instability mode shapes are identified. It is shown that the first transverse and planar instability modes resemble nonplanar saddle-like and planar elliptic shapes, respectively.Des méthodes de milieux continus pour la modélisation de bicouches lipidiques sont développées et appliquées à des vésicules lipidiques à deux phases et à des particules discoïdes de lipoprotéines de haute densité (HDL). Tout d'abord, en s'appuyant sur un modéle tridimensionnel, la mécanique d'une bicouche lipidique possédant une courbure spontanée est considérée. La Cinématique, la symétrie matérielle, les relations de stress, et la cohérence de bicouches lipidiques sont discutées. En traitant une bicouche lipidique comme une structure mince, la densité d'énergie surfacique d'une bicouche lipidique ayant une courbure spontanée est obtenue à l'aide d'une procédure de réduction de dimension. L'attention est portée sur la source de courbure spontanée de la densité d'énergie bien connue de Canham–Helfrich. En outre, l'effet de l'asymétrie constitutive des sur la densité d'énergie surfacique d'une bicouche lipidique est mis en évidence. Considérant une vésicule à deux phases comme système de domaines sphériques coexistants, son équilibre est étudié à l'aide d'un modèle simple de milieu continu. Des configurations multi-domaines et de l'état fondamental sont considérées. Alors que, dans le premier cas, plusieurs domaines lipidiques bourgeonnés coexistent sur une vésicule, dans le dernier cas, la vésicule est composée de deux grands domaines lipidiques. La variation de l'énergie potentielle nette d'une vésicule multi-domaine en fonction du nombre de domaines lipidiques et de la pression osmotique est étudiée. En se basant sur la comparaison de l'énergie, deux configurations de l'état fondamental correspondant à des niveaux d'énergie minimaux sont identifiés: la configuration étranglée et la sphère complète. Les résultats indiquent que la pression osmotique et le rayon excédentaire initial jouent un rôle clé dans la forme finale des configurations à l'état fondamental. Les valeurs critiques de ces paramètres sont identifiées. Enfin, l'équilibre et la stabilité d'une particule HDL discoïde sont étudiés. Un modèle dans lequel la bicouche lipidique et les composants d'ApoA-I à double bande de la particule de HDL discoïde sont représentées par une surface de matériau et une courbe de matériau parfaitement collée sur le bord de la surface est proposé. L'énergie de courbure et la tension de surface de la bicouche lipidique ainsi que l'énergie de flexion de la chaîne apoA-I sont incluses. En adoptant un schéma variationnel, les équations d'équilibre non-linéaire d'une particule de HDL discoïdale dans une configuration générale sont calculées d'après des formulations directes, basées sur la géométrie, ou paramétrées. Les équations d'équilibre linéarisées d'une particule de HDL circulaire plane sont obtenues et sa stabilité linéaire est étudiée en utilisant la seconde méthode de variation. Une méthode de comparaison de l'énergie est appliquée et se trouve à offrir une approche pratique pour déterminer la stabilité linéaire. Des résultats numériques sont présentés pour l'équilibre et la stabilité des particules de HDL circulaires planes. Un plan de stabilité indiquant différentes régions stables et instables des paramètres d'entrée adimensionnels sous-jacents est fourni. Certaines possibilités de changement de stabilité et les formes modales d'instabilité sont identifiées. Il est démontré que les premiers modes d'instabilité transversale et plane ressemblent aux formes de selle non planes et d'ellipse plane, respectivement.
9
Peter, Samuel N. K. „Polymerized-depolymerized Vesicles : reversible thiol-disulfide-based phosphatidylcholine membranes /“. Ann Arbor : Univ. Microfilms Intern, 1988. http://www.gbv.de/dms/bs/toc/016151828.pdf.
Der volle Inhalt der Quelle
10
Connell, Karen Elizabeth. „Studies of transport through curved and planar lipid bilayers /“. Title page, contents and summary only, 1990. http://web4.library.adelaide.edu.au/theses/09PH/09phc7522.pdf.
Der volle Inhalt der Quelle
11
Carpenter, M. L. „The interaction of pressure and anaesthetics with lipid bilayers“. Thesis, University of Salford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376841.
Der volle Inhalt der Quelle
12
Crowell, Kevin James. „Solid state deuterium nuclear magnetic resonance investigation of the interaction of positively-charged polyelectrolytes with negatively-charged lipid bilayer membrane vesicles“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq29221.pdf.
Der volle Inhalt der Quelle
13
Dennison, Andrew. „Neutron reflectivity studies of insulin and phosphatidylcholine floating lipid bilayers“. Thesis, University of Sheffield, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.574586.
Der volle Inhalt der Quelle
14
Adrien, Berthault. „Molecular simulation of mixtures in lipid bilayers“. Doctoral thesis, Universitat Rovira i Virgili, 2018. http://hdl.handle.net/10803/664727.
Der volle Inhalt der QuelleAnnotation:
L'objectiu principal d'aquesta tesi doctoral és estendre un mètode ràpid i fiable (camp simple de mitjana cadena) per estudiar barreges en equilibri i en particular mescles de lípids i petits col·loides inserits en membranes lipídiques, capaços de considerar la presència de components addicionals i unir models de simulació molecular i teories elàstiques per membranes anfifíliques. Per aconseguir aquest objectiu, proposem parametritzar els paràmetres amb el mètode de camp de mitjana cadena simple per reproduir les característiques de les bicapes de lípids DMPC en equilibri comparant amb resultats de simulació publicats prèviament i dades experimentals. La tesi presenta el treball realitzat per assolir els objectius específics d'aquesta tesi doctoral: dades moleculars fiables completament parametritzats capaços de reproduir el comportament de les membranes lipídiques amb un únic tipus de component, l'estudi de les seves propietats d'equilibri interactuant amb molècules addicionals i els seus efectes en la línia de tensió per al cas específic de la creació de porus i un enfocament dinàmic per a l'estudi de la dinàmica de les membranes fetes de diverses cadenes anfifíliques, en particular en presència de porusEl objetivo principal de esta tesis doctoral es extender un método rápido y confiable (campo simple de media cadena) para estudiar mezclas en equilibrio y en particular mezclas de lípidos y pequeños coloides insertados en membranas lipídicas, capaces de considerar la presencia de componentes adicionales y unir modelos de simulación molecular y teorías elásticas para membranas anfifílicas. Para lograr este objetivo, proponemos parametrizar los parámetros con el método de campo de media cadena simple para reproducir las características de las bicapas de lípidos DMPC en equilibrio comparando con resultados de simulación publicados previamente y datos experimentales. La tesis presenta el trabajo realizado para alcanzar los objetivos específicos de esta tesis doctoral: datos moleculares fiables completamente parametrizados capaces de reproducir el comportamiento de las membranas lipídicas con un único tipo de componente, el estudio de sus propiedades de equilibrio interactuando con moléculas adicionales y sus efectos en la línea de tensión para el caso específico de la creación de poros y un enfoque dinámico para el estudio de la dinámica de las membranas hechas de varias cadenas anfifílicas, en particular en presencia de poros
The main goal of this Doctoral thesis is to extend a fast and reliable method (Single Chain Mean Field) to study mixtures at equilibrium and in particular mixtures of lipids and small colloids inserted into lipid membranes, able to consider the presence of additional components and bridge molecular simulation models and elastic theories for amphiphilic membranes. In order to achieve this objective, we proposed to parametrise the parameters for the Single Chain Mean Field method to reproduce the features of DMPC lipid bilayers at equilibrium involving comparisons with previously published simulation results and experimental data. The thesis reports the work performed to achieve the specific objectives of this doctoral thesis: reliable fully parametrised molecular details able to reproduce the behaviour of lipid membranes made of a single type of component, the study of their equilibrium properties interacting with additional molecules and their effects on the line tension for the specific case of the pore creation and a dynamical approach to study the dynamics of membranes made of various amphiphilic chains, in particular in the presence of pores.
15
Tickner, A. L. „The form and function of MP26 in artificial membranes and liposomes“. Thesis, University of East Anglia, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294658.
Der volle Inhalt der Quelle
16
Bandegi, Sanaz. „INTERACTION OF FLUORESCENT LIPID DYES WITH LIPID VESICLES AND SUPPORTED LIPID BILAYERS AND THEIR APPLICATIONS“. Diss., Temple University Libraries, 2019. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/584744.
Der volle Inhalt der QuelleAnnotation:
ChemistryPh.D.
Lipophilic dye probes are widely used for labelling of cells, organelles, liposomes, viruses and lipoproteins. The lipophilic dye diffuses in the membrane and stains the cell and cells even tolerate the lipophilic dye in high concentration. The fluorescence of styryl dyes increases after insertion into the hydrophobic environment of the lipid membrane compared their fluorescence in the aqueous phase solution. The alkyl chains of the fluorescent styryl dye probe insert into membranes and are used to understand their biophysical properties and their behavior in lipid bilayers. The mechanism of incorporation of the dyes into cell membranes, or vesicle model systems, is not resolved. In this study we used a modified dialkylaminostyryl fluorescent lipid, 4-(4-(dihexadecylamino)styryl)-N-methylpyridinium iodide (DiA), replacing the I- counterion with the Cl- anion to make DiA-Cl increase hydration of the polar head and to enable self-assembling in water and formation of vesicles. Vesicles composed of DMPC (1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine)/DiA, DPPC (1,2-dipalmitoyl-sn-glycero-3- phosphatidylcholine) /DiA, DSPC (1,2-distearoyl-sn-glycero-3- phosphatidylcholine) /DiA, DMPE (1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine)/DiA, DPPE (1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine)/DiA and DSPE (1,2-distearoyl-sn-glycero-3-phosphoethanolamine)/DiA have been prepared in mole ratios between 100/0 to 0/100, in order to investigate the effects of chain length and headgroup type on chain packing and phase separation in these mixed amphiphilic systems, using nanocalorimetry, dynamic light scattering and fluorescence data, as well as confocal laser scanning microscopy (CLSM) and cryo-transmission electron microscopy (Cryo-TEM). In addition, we report the self-assembly of DiA-Cl, to form H-aggregates of lipid bilayers in aqueous solution, beyond a critical vesicle concentration. Lipid bilayers can be fused onto silica nanoparticles (NPs) to form supported lipid bilayer (SLB)-NPs. (SLB)-NPs have a varous interdisciplinary applications from medicine to environmental fields and agriculture sciences. Here, the lipids on the nanoparticles were used for two applications. One was to adsorb polycyclic aromatic hydrocarbons (PAHs) from the environment and the other was as vehicles for foliar delivery of nutrients to plants. Silica SLB nanoparticles can increase the solubility of Benzo[a]Pyrene (BaP) in order to extract the BaP from soil for in situ biodegradation. Initial studies were begun on the effect of foliar application of silica SLBs nanoparticles on plants. The SLBs to be used were prepared using both 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and DiA, in order to determine whether the lipid increased the entry of the silica into the plant leaves and whether the lipids also entered.
Temple University--Theses
17
Danial, John Shokri Hanna. „Imaging lipid phase separation on droplet interface bilayers“. Thesis, University of Oxford, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.711943.
Der volle Inhalt der Quelle
18
Lee, Chongsoo. „Raman spectroscopy of supported lipid bilayers and membrane proteins“. Thesis, University of Oxford, 2005. http://ora.ox.ac.uk/objects/uuid:76f4be6e-b7d3-46c5-a2a1-3dcc7a399410.
Der volle Inhalt der QuelleAnnotation:
Off-resonance unenhanced total internal reflection (TIR) Raman Spectroscopy was explored to investigate supported single lipid bilayers with incorporated membrane peptides/proteins at water/solid interface. A model membrane was formed on a planar supported lipid layer (pslb) by the fusion of the reconstituted small unilamellar vesicles (SUVs), and the intensity of bilayer was confirmed by a comparison of Raman spectral intensity in the C-H stretching modes with C16TAB. With prominent Raman sensitivity attained, we studied the 2-D phase transition of DMPC and DPPC pslbs and the temperature-dependent polarised spectra revealed a broad transition range of ca. 10 °C commencing at the calorimetric phase transition temperature. We applied polarised TIR-Raman Spectroscopy to pslbs formed by DMPC SUVs reconstituted with a model membrane-spanning peptide gramicidin D. A preferential channel structure formed by dissolution of trifluoroethanol could be probed by polarised Raman Spectroscopy qualitatively showing an antiparallel β-sheet conformation (different from "standard" one) and our Raman spectra by correlation with NMR and CD data confirmed single-stranded π6.3 β-helical channel structure in the single bilayer. We also studied the membrane-penetrating peptide indolicidin in the presence of DMPC pslb over the chain melting temperature and a β-turn structure was dominantly observed concomitant with membrane perturbation. Dynamic adsorption of DPPC to form pslb from a micellar solution of n-dodecyl-β- D-maltoside could be examined with high sensitivity of every 1-min acquisition. Finally we used polarised TIR-Raman scattering to porcine pancreatic phospholipase A2 hydrolytic activity on DPPC pslbs and revealed lipid-active conformation different from that of the enzyme alone.
19
Hussein, Wourood. „Nanoparticle-supported lipid bilayers : A novel approach to introduce curvature in model membranes“. Thesis, Umeå universitet, Institutionen för integrativ medicinsk biologi (IMB), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-179003.
Der volle Inhalt der Quelle
20
Ugail, Hassan, N. Jamil und R. Satinoianu. „Method of numerical simulation of stable structures of fluid membranes and vesicles“. WSEAS, 2006. http://hdl.handle.net/10454/2751.
Der volle Inhalt der Quelle
21
Wu, Diana. „Effect of membrane thickness and unsaturation on dye efflux rates induced by [delta]-Lysin from phosphatidylcholine vesicles /“. Electronic version (PDF), 2005. http://dl.uncw.edu/etd/2005/wud/dianawu.pdf.
Der volle Inhalt der Quelle
22
Gater, Deborah Lynne. „Effects of cholesterol on the structure, ordering and dynamics of lipid bilayers and membranes“. Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.508792.
Der volle Inhalt der Quelle
23
Brandt, Erik G. „Molecular Dynamics Simulations of Fluid Lipid Membranes“. Doctoral thesis, KTH, Teoretisk biologisk fysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-42586.
Der volle Inhalt der QuelleAnnotation:
Lipid molecules form thin biological membranes that envelop all living cells, and behave as two-dimensional liquid sheets immersed in bulk water. The interactions of such biomembranes with their environment lay the foundation of a plethora of biological processes rooted in the mesoscopic domain - length scales of 1-1000 nm and time scales of 1-1000 ns. Research in this intermediate regime has for a long time been out of reach for conventional experiments, but breakthroughs in computer simulation methods and scattering experimental techniques have made it possible to directly probe static and dynamic properties of biomembranes on these scales. Biomembranes are soft, with a relatively low energy cost of bending, and are thereby influenced by random, thermal fluctuations of individual molecules. Molecular dynamics simulations show how in-plane (density fluctuations) and out-of-plane (undulations) motions are intertwined in the bilayer in the mesoscopic domain. By novel methods, the fluctuation spectra of lipid bilayers can be calculated withdirect Fourier analysis. The interpretation of the fluctuation spectra reveals a picture where density fluctuations and undulations are most pronounced on different length scales, but coalesce in the mesoscopic regime. This analysis has significant consequences for comparison of simulation data to experiments. These new methods merge the molecular fluctuations on small wavelengths, with continuum fluctuations of the elastic membrane sheet on large wavelengths, allowing electron density profiles (EDP) and area per lipid to be extracted from simulations with high accuracy. Molecular dynamics simulations also provide insight on the small-wavelength dynamics of lipid membranes. Rapidly decaying density fluctuations can be described as propagating sound waves in the framework of linearized hydrodynamics, but there is a slow, dispersive, contribution that needs to be described by a stretched exponential over a broad range of length- and time scales - recent experiments suggest that this behavior can prevail even on micrometer length scales. The origin of this behavior is discussed in the context of fluctuations of the bilayer interface and the molecular structure of the bilayer itself. Connections to recent neutron scattering experiments are highlighted.QC 20111014
Modelling of biological membranes
24
Davis, Joseph E. „Refinement, validation, and application of a charge equilibration force field for simulations of phospholipid bilayers“. Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 67 p, 2009. http://proquest.umi.com/pqdweb?did=1885474371&sid=2&Fmt=2&clientId=8331&RQT=309&VName=PQD.
Der volle Inhalt der Quelle
25
Alramadan, Ghada. „The Effect of Styrene-Maleic Acid (SMA) Copolymers on Solubilizing Lipid Bilayers and Forming Nanodiscs“. PDXScholar, 2018. https://pdxscholar.library.pdx.edu/open_access_etds/4843.
Der volle Inhalt der QuelleAnnotation:
Cell membranes, or plasma membranes, play an essential role in the structure and the function of living cells. In 1972, the fluid mosaic membrane model was the first unifying paradigm of membrane structure. It is no longer considered adequate because evidence of many non-homogeneous lipid structures in both natural and model membranes have been discovered over the past thirty years. The field of membrane biophysics now uses updated versions of the mosaic model, which consists of the complex mixture of different lipid species. The lipid species found in natural membranes produce a range of dynamic, laterally segregated, non-homogeneous domains, which exist on time scales ranging from microseconds to minutes. The cell membrane is an enclosing or separating membrane that acts as a selectively permeable barrier within living things. It consists of the phospholipid bilayer with associated embedded proteins, integral (intrinsic) and peripheral (extrinsic) proteins used for various biological activities. Proteins, especially integral membrane proteins, perform a range of key functions vital to the cell, such as controlled movement of molecules across lipid bilayers, as well as participating in cell signaling and motility. The major obstacle to studying membrane proteins is the tendency for some of their properties to change and the proteins themselves may be denatured when extracted by detergents. One of the most significant approaches to solve this problem is the use of styrene-maleic acid copolymers (SMAs), which offers detergent-free solubilization of embrane, which allows studies of membrane proteins to be done in very small systems. The main goal of this thesis is to examine the effects of these polymers on the interior of the lipid bilayer. With these, membrane proteins can be extracted from cell membranes while conserving a patch of near-native membrane around them. It has been suggested but not proven that proteins in nanodiscs reside in a hydrophobic environment that is identical to that found in the native cell membrane. Moreover, I also investigate the kinetics of membrane solubilization by SMA by using UV/visible spectrophotometer. In addition, I examine how lipid packing in the nanodiscs is affected by the presence of the polymers and how it depends on polymer composition by using SMA variants with different styrene-to-maleic acid ratios.
26
Cama, Jehangir. „Quantifying passive drug transport across lipid membranes“. Thesis, University of Cambridge, 2016. https://www.repository.cam.ac.uk/handle/1810/254296.
Der volle Inhalt der QuelleAnnotation:
Antibiotic resistance has emerged as one of the World's leading public health challenges. The inexorable emergence of drug resistant pathogens, combined with a steep decline in antibacterial drug discovery, has led to a major crisis. One of the most common drug resistance mechanisms involves bacteria adapting to reduce intracellular drug accumulation. To understand these resistance mechanisms, one needs quantitative information about the membrane permeability of drugs. In this Thesis, we develop a novel optofluidic permeability assay that allows us to quantify the permeability coefficient of drugs crossing lipid membranes. Lipid vesicles are used as model systems and drug molecules are tracked directly using their autofluorescence in the ultraviolet. The permeability coefficient of the drug is inferred by studying the increase in drug autofluorescence intensity within vesicles as they traverse a microfluidic network while exposed to the drug for well defined times. This provides a novel platform from which we can develop membrane models for understanding drug permeability. We incorporate the Escherichia coli outer membrane protein OmpF in vesicles and quantify its role in the transport of fluoroquinolone antibiotics. We provide direct visualisation of OmpF mediated fluoroquinolone transport. We study the pH dependence of antibiotic transport both through pure phospholipid membranes and through OmpF, and present a physical mechanism to explain the pH dependence of E. coli fluoroquinolone susceptibility. We also show the importance of lipid composition on drug permeability - changing the lipid composition of the membrane is shown to change antibiotic permeability by over an order of magnitude. Finally, we report on the discovery of a novel signalling mechanism in E. coli that relies on the transport of small drug-like molecules, and discuss the role it plays in stress response in the microbial community.
27
Speijer, Johan Gerhard. „Studies on the chemical nature of procoagulant sites on phospholipid vesicles and platelet membranes“. Maastricht : Maastricht : Rijksuniversiteit Limburg ; University Library, Maastricht University [Host], 1987. http://arno.unimaas.nl/show.cgi?fid=5398.
Der volle Inhalt der Quelle
28
Juodeikis, Rokas. „Engineering membranes in Escherichia coli : the magnetosome, LemA protein family and outer membrane vesicles“. Thesis, University of Kent, 2016. https://kar.kent.ac.uk/61062/.
Der volle Inhalt der QuelleAnnotation:
Magnetosomes are membranous organelles found in magnetotactic bacteria (MTB). The organelle consist of ferromagnetic crystals housed within a lipid bilayer chained together by an actin-like filament and allows MTB to orient within magnetic fields. The genetic information required to produce these organelles has been linked to four different operons, encoding for 30 genes. These membranous organelles and the magnetic minerals housed within have various biotechnological applications, therefore enhanced recombinant production of such structures in a model organism holds significant potential. The research described in this thesis is focuses on the production of recombinant magnetosomes in the model organism Escherichia coli. Cloning the genes involved in the generation of the organelle individually or in various combinations resulted in the construction of over 100 different plasmids, compatible with the model organism. SDS-PAGE and electron microscopy analysis was used to characterise E. coli cells harbouring these constructs. The observation of electron dense particles, arranged in a chain structure, show that magnetosome generation in the model organism is possible, but is highly dependent on the growth conditions used. The need for specific growth conditions is later backed up by the analysis of the maturation of the cytochrome c proteins involved in magnetosome biomineralisation, which can only be correctly processed under certain conditions. Individual production of two different magnetosome proteins, MamQ or MamY, allowed the generation of various membranous structures in E. coli observed in 48.9% and 56.2% of the whole population of cells respectively. Combinations of these with MamI, MamL or MamB in a variety of combinations led to a variation in the phenotype observed. Bioinformatics analysis of MamQ led to the discovery of a novel membrane restructuring protein family, the LemA protein family, present in a broad range of bacteria. Four different LemA proteins from Bacillus megaterium, Clostridium kluyveri, Brucella melitensis or Pseudomonas aeruginosa were then produced in E. coli and the analysis of the resulting strains revealed the presence of novel intracellular membranous structures which vary in size, form and localisation. Furthermore, when attempts were made to target these proteins for the modification of the outer membrane, a mechanism for increased outer membrane vesicle generation was serendipitously discovered and different effects of these proteins were once again observed. Together, the results described shows good evidence for recombinant magnetosome production in E. coli and opens a new avenue of membrane engineering in this commonly used organism. Such membranous structures have various biotechnological applications, such as enhanced metabolic engineering potential or specialised lipid vesicle production.
29
Domènech, Cabrera Òscar. „Structure and Physicochemical Properties of Phospholipidic Monolayers and Bilayers. LB and AFM Studies“. Doctoral thesis, Universitat de Barcelona, 2007. http://hdl.handle.net/10803/2758.
Der volle Inhalt der QuelleAnnotation:
The main objective of this Ph. D. Thesis work was to study the physicochemical properties of the inner membrane of mitochondria and the interaction of "cyt c" with model membranes. Suitable techniques were used to accomplish this objective: Langmuir and Langmuir Blodgett films, fluorescence spectroscopy, Brewster Angle Microscopy and Atomic Force Microscopy.The general conclusion of this Thesis is: "Calcium induces HII phases in POPE:CL (0.8:0.2, mol:mol) samples in solution. This composition is the most stable mixed monolayer of both phospholipids and corresponds to the native molar fraction in the inner membrane of the mitochondrion. The extension of these inverted micelles forms planar bilayers on solid supports displaying lateral lipid segregation of CL enriched domains where cyt "c can" bind specifically. In this configuration POPC can remain as a spacer in POPE enriched domains forming the matrix of the membrane". The inverse process would be a possible vindication to the release of "cyt c" from the inner membrane of mitochondrion during apoptosis.
30
Chantemargue, Benjamin. „In silico investigation of xenobiotic interactions with lipid bilayers and ABC membrane transporters, the case of ABCC4/MRP4“. Thesis, Limoges, 2018. http://www.theses.fr/2018LIMO0077/document.
Der volle Inhalt der QuelleAnnotation:
L’appréhension des mécanismes d’action biologiques des protéines membranaires nécessite de comprendre les interactions des xénobiotiques avec ces protéines et avec les membranes lipidiques. Les méthodes expérimentales sont parfois coûteuses et ne permettent d’obtenir que des informations partielles sur les interactions xénobiotiques-membrane-protéine. La modélisation moléculaire est une sérieuse alternative. Les simulations de dynamique moléculaire et de dynamique biaisées ont ouvert de nombreuses perspectives en permettant de décrire ces interactions moléculaires à l’échelle atomique. Grâce à des simulations de dynamique moléculaire, nous avons été capables de construire un modèle de transporteur humain ABC : ABCC4/MRP4. Cette protéine a été choisie pour sa présence dans le rein, notamment, et son importance clinique. Nous avons évalué l’influence du cholestérol sur cette protéine. L’étude de domaines spécifiques et l’impact d’un polymorphisme a été reliée à l’activité de transport de cette protéine. Nous avons également étudié l’interaction de xénobiotiques avec ce transporteur humain. Le cycle de transport des transporteurs ABC a été examiné afin de comprendre leur fonctionnement. L’incorporation de cholestérol a montré un impact significatif sur la protéine humaine ABCC4/MRP4 et sur les xénobiotiques étudiés. L’importance de domaines constituant la protéine ABCC4/MRP4 ainsi que l’importance de résidus individuels a clairement été prouvée. Nous avons également pu observer des intermédiaires du cycle de transport d’un transporteur ABC conjointement avec des changements structurauxUnderstanding the biological mechanisms of action of membrane proteins requires the comprehension of the interactions of xenobiotics with these proteins and with lipid membranes. Experimental methods are often demanding and only partially respond to xenobiotic-membrane-protein interactions. In silico molecular modeling is a serious alternative to tackle these issues. Molecular dynamics (MD) and biased dynamics simulations have opened many perspectives by providing an atomistic description of these intermolecular interactions. Using MD simulations, we built a model of the human ABC ABCC4/MRP4 transporter. We explored the influence of cholesterol on this protein as well as the impact of a polymorphism known to shut down the transport activity of this protein. We also studied the interaction of xenobiotics with this human transporter. The transport cycle of the ABC transporters was investigated in an attempt to better understand how it works.Interactions between lipid membranes and xenobiotics were explored by examining their ability to incorporate lipid membranes. Lipid mixtures with cholesterol showed a significant impact on the human protein ABCC4/MRP4 and on the xenobiotics studied. The importance of regions, domains constituting the ABCC4/MRP4 protein as well as the importance of specific residues has been clearly demonstrated. We also observed intermediates in the transport cycle of an ABC transporter in conjunction with structural changes occurring during this cycle
31
Wessman, Per. „Physico-Chemical Investigations of, and Characterization of Model Membranes for, Lipid-Peptide Interactions“. Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-89432.
Der volle Inhalt der Quelle
32
Subramaniam, Varuni. „Preparation and Characterization of Novel Lipid and Proteolipid Membranes from Polymerizable Lipids“. Diss., The University of Arizona, 2006. http://hdl.handle.net/10150/194889.
Der volle Inhalt der QuelleAnnotation:
The work described here has focused on two types of supramolecular assemblies, supported lipid bilayers (SLBs) and giant vesicles (GVs) from polymerizable lipids. SLBs are explored extensively as structural models in biophysical studies of cell membranes and biosensor coatings. With regard to implementation as biocompatible scaffoldings for receptor-based molecular devices, fluid SLBs lack chemical, thermal and mechanical stability as lipids are self-organized by weak, noncovalent forces. One possible solution is to use synthetic lipid monomers that can be polymerized to form robust bilayers. A key question is how polymerization affects transmembrane protein structure and activity. Specifically it is unclear if lipid cross-linking can be achieved without adversely affecting the activity of incorporated proteins. In this work the effect of lipid polymerization on transmembrane protein activity was studied with rhodopsin. The protein was reconstituted into SLBs composed of polymerizable lipids, bis-SorbPC, bis-SorbPC:mono-SorbPC, bis-DenPC and bis-SorbPC:mono-SorbPE. Rhodopsin photoactivity was monitored using plasmon waveguide spectroscopy. The results show that reconstitution of rhodopsin into SLBs composed of phosphatidylcholine with the polymerizable moiety in the acyl chain terminus, followed by photoinduced cross-linking of the lipids, does not significantly perturb protein function. A possible explanation is that a bilayer with relatively low Xn retains sufficient elasticity to accommodate the membrane deformation that accompanies the conformational change associated with rhodopsin photoactivation when polymerized in the acyl chain terminus. GVs have diameters ranging from several to few hundred micrometers and thus can be observed by optical microscopic methods. This allows manipulation of individual vesicles and observation of their transformations in real time. GVs have attracted attention as microcontainers for enzymes and drugs, and as biosensors. With the aim of increasing stability for these types of applications, GVs were prepared from synthetic dienoyl lipids that can be polymerized to form robust vesicles. The stability of these vesicles after polymerization was investigated by surfactant treatment, drying and rehydration, and temperature variations. The structure of poly(GVs) was largely retained under these conditions which destroy unpolymerized vesicles. Permeability studies on poly(GVs) suggests that they could be potentially used in a variety of technological applications, including sensors, macromolecular carriers, and microreactors.
33
Le, Marois Alix Marie. „Multi-parameter imaging of lipid bilayers and cell membranes using time- and polarisation-resolved fluorescence microscopy“. Thesis, King's College London (University of London), 2018. https://kclpure.kcl.ac.uk/portal/en/theses/multiparameter-imaging-of-lipid-bilayers-and-cell-membranes-using-time-and-polarisationresolved-fluorescence-microscopy(5f4611d0-362e-48df-95df-9b43d2750a7c).html.
Der volle Inhalt der QuelleAnnotation:
This thesis presents the development and application of multi-dimensional ̨uorescence imaging based on confocal microscopy and time-correlated single photon counting (TCSPC) instrumenta-tion, to reveal the relationship between microenvironment and order parameters of lipid bilayers, which are the fundamental entities of cell membranes. The objective is to use all the informa-tion available from the ̨uorescence signal - emission wavelength, lifetime and polarisation - to independently interrogate several biophysical properties of biomembranes, simultaneously. The photophysical characterisation of membrane dye laurdan was carried out using ̨uorescence spectroscopy, and this showed that its emission wavelength and ̨uorescence lifetime report on dif-ferent characteristics of its environment, namely, hydration and polarity. Time-resolved anisotropy measurements were used to report on two membrane order parameters related to the hindered ro-tational di ̇usion of the ̨uorophore in the bilayer. An experimental and analytical framework was implemented in order to measure and quantify these four parameters, on the same ̋eld of view. This method was then applied to the extensive characterisation of the relationship between these membrane properties in arti ̋cial bilayers, and showed distinct dependence of membrane microen-vironment and order to temperature and to membrane chemistry, i.e. the degree of saturation and cholesterol content. This approach also proved informative in resolving the dynamics of domain mixing in ternary lipid mixtures. Applied to the membranes of live cells, simultaneous imaging of membrane micro-environments and order parameters showed that while plasma and internal membranes display di ̇erent membrane polarity and order parameter values, linked to their di ̇er-ent chemical composition, the relationship between these parameters is preserved throughout the cell. The role of cholesterol in the preservation of these parameters was investigated, showing that cholesterol strongly determines membrane hydration and polarity, while the order parameters are less sensitive to modulation of cholesterol content. Interpretation of spectral and lifetime informa-tion allowed discrimination between the e ̇ect of cholesterol on membrane hydration and polarity. Cell-derived plasma membrane vesicles were also characterised as a system to study lipid bilayers with compositions more faithful to that of the cell membrane, and results suggest that the lipid content of such vesicles is strongly determined by the modalities of their formation. Lastly, strategies to improve the analysis of multi-dimensional time-resolved ̨uorescence image data were explored. A novel processing routine based on principal component analysis was created, allowing sensitive detection of lifetime contrast in photon-limited TCSPC images, and the potential to analyse time-resolved anisotropy data in a pixel-wise fashion was also demonstrated.
34
Elliott, Richard. „Phase separation in mixed bilayers containing saturated and mono-unsaturated lipids with cholesterol as determined from a microscopic model /“. Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/9675.
Der volle Inhalt der Quelle
35
Albertorio, Fernando. „Supported phospholipid membranes as biometric labs-on-a-chip: analytical devices that mimic cell membrane architectures and provide insight into the mechanism of biopreservation“. Texas A&M University, 2003. http://hdl.handle.net/1969.1/5923.
Der volle Inhalt der QuelleAnnotation:
This dissertation focuses on the applications of solid supported phospholipid
membranes as mimics of the cellular membrane using lab-on-a-chip devices in order to
study biochemical events such as ligand-receptor binding and the chemical mechanism
for the preservation of the biomembrane. Supported lipid bilayers (SLBs) mimic the
native membrane by presenting the important property of two-dimensional lateral
fluidity of the individual lipid molecules within the membrane. This is the same
property that allows for the reorganization of native membrane components and
facilitates multivalent ligand-receptor interactions akin to immune response, cell
signaling, pathogen attack and other biochemical processes.
The study is divided into two main facets. The first deals with developing a
novel lipopolymer supported membrane biochip consisting of Poly(ethylene glycol)
(PEG)-lipopolymer incorporated membranes. The formation and characterization of the
lipopolymer membranes was investigated in terms of the polymer size, concentration
and molecular conformation. The lateral diffusion of the PEG-bilayers was similar to
the control bilayers. The air-stability conferred to SLBs was determined to be more effective when the PEG polymer was at, or above, the onset of the mushroom-to-brush
transition. The system is able to function even after dehydration for 24 hours. Ligandreceptor
binding was analyzed as a function of PEG density. The PEG-lipopolymer acts
as a size exclusion barrier for protein analytes in which the binding of streptavidin was
unaffected whereas the binding of the much larger IgG and IgM were either partially or
completely inhibited in the presence of PEG.
The second area of this study presents a molecular mechanism for in vivo
biopreservation by employing solid supported membranes as a model system. The
molecular mechanism of how a variety of organisms are preserved during stresses such
as anhydrobiosis or cryogenic conditions was investigated. We investigated the
interaction of two disaccharides, trehalose and maltose with the SLBs. Trehalose was
found to be the most effective in preserving the membrane, whereas maltose exhibited
limited protection. Trehalose lowers the lipid phase transition temperature and
spectroscopic evidence shows the intercalation of trehalose within the membrane
provides the chemical and morphological stability under a stress environment.
36
Ratnayaka, Saliya Nalin. „Formation and Characterization of Hybrid Bilayers and Diffusion of Cations Across Liposomal Membranes: Studies Based on Polymerizable Lipids“. Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/194428.
Der volle Inhalt der QuelleAnnotation:
Cellular energy transduction processes are often driven by transmembrane ion gradients, and a number of artificial membrane systems have been developed that allow for chemically or light-induced transport of ions across lipid bilayers. These liposomal architectures, however, are not readily interfaced to a solid-state transducer. A significant step toward this goal is described here by assessing the possibility of coupling a lipid bilayer directly to a transducer to form a stable uniform film using hybrid bilayer membranes (HBMs).Although the surface attachment of self-assembled monolayer increases the robustness of the lipid assembly, HBMs cannot maintain film uniformity under harsher conditions due to the absence of strong lipid-lipid interactions. Therefore, HBMs were prepared and characterized using a cross-linking polymerizable lipid, bis-SorbPC. Several parameters relating to lipid deposition and film stabilization through polymerization were examined. Film characterization strongly suggests that polymerization of bis-SorbPC stabilizes the HBM such that its structure is largely preserved even after the dehydration process. This work suggests that network formation in the upper monolayer is not enough to prevent oligomer desorption, intermonolayer covalent linking is also a prerequisite in making uniform, defect-free planar supported lipid assemblies.Some of the challenges associated with the application of lipids involve the creation of supported bilayers that are stable to chemical and physical disruptions, yet retain their ion barrier properties, and allow transmembrane ion transport by lipid-soluble shuttles. Polymerized lipid films provide the stability required for these structures, but permeability properties of cations across poly(lipid) membranes are not known. Therefore, convenient liposome-based proton and calcium permeability assays were developed. These assays were applied to various poly(lipid) compositions.In addition, three novel sorbyl-substituted head group polymerizable lipids, which have been synthesized based on a strategy that head group polymerization would minimally perturb the characteristic ion impermeability of the membrane, were evaluated for their lipid characteristics and ability to form polymers. None of these compounds forms vesicles by itself. Therefore, attempts were made to form mixed vesicles with other fluid lipids. The miscibility of the mixed monolayers was assessed using Langmuir isotherms.
37
Karamdad, Kaiser. „Development of microfluidic platforms to construct giant unilamellar vesicles (GUVs) for the biophysical study of lipid membranes“. Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/56915.
Der volle Inhalt der QuelleAnnotation:
This thesis presents the design, development and application of several platforms through which to generate giant vesicles for biophysical and mechanical membrane studies. There has been a growing focus on manufacturing model membrane systems with improved throughput and structural properties in recent years. GUVs are a popular model membrane system for studying lipid membrane-associated phenomena due to their inherent similarity to biological cells. Traditional methods to construct vesicles offer little control over nuanced membrane properties such as asymmetry and patterning, which has paved the way for more refined techniques to be developed. This thesis details the development of a microfluidic platform technology that addresses this chasm in sophisticated GUV fabrication strategies. The technique presented offers control over key structural features such as vesicle size dispersity, internal content, membrane composition and asymmetry. Vesicles were investigated using contour detection and fluctuation analysis in order to quantify the bending rigidity in membranes constructed by microfluidics for the very first time. Furthermore, the emulsion phase transfer (EPT) method was refined for the construction of GUVs with phase separated membranes across three of compositions. This is the first investigation concerning domain formation in membranes constructed from emulsion precursors at a range of a compositions. The progress made in advancing platform technologies opens up various avenues through which to further explore biophysical phenomena such as a lipid flip-flop dynamics, as well as for the high-throughput generation of artificial cell systems, with potential relevance for therapeutic applications such as smart drug delivery.
38
Fox, Helen Mary. „Toca-1 driven actin polymerisation at membranes“. Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/275610.
Der volle Inhalt der QuelleAnnotation:
Regulation of the actin cytoskeleton is key to cellular function and underlies processes including cell migration, mitosis and endocytosis. Motile cells send out dynamic actin protrusions that enable them to sense and interact with their environment, as well as generating physical forces. Linking of the actin cytoskeleton to the cell membrane is essential for the formation of these protrusions. The proteins that are thought to fulfil such a role have a membrane interacting domain (such as the PH domain in lamellipodin, or I-BAR protein in IRSp53) and a domain which interacts with actin regulatory proteins (such as the SH3 domain of IRSp53, which binds Ena and VASP). I investigated the contribution of the F-BAR protein Toca-1 in linking actin polymerisation to membranes, by characterising a new protein-protein interaction and the interaction of Toca-1 with giant unilamellar vesicles. FBP17, a homologue of Toca-1, can oligomerise to form 2D flat lattices and 3D tubules on membranes. Proteins of the Toca-1 family have previously been implicated in actin polymerisation in cell-free systems and during endocytosis. However, there is emerging evidence that Toca-1 family proteins could also be involved in the formation of outward facing protrusions, lamellipodia and filopodia. In an in vitro system that recapitulates the formation of filopodia-like structures (FLS) on supported lipid bilayers, Toca-1 is recruited early, suggesting a Toca-1 scaffolding mechanism could precede the recruitment of other actin regulators. One prediction of this model is that Toca-1 would bind proteins previously implicated in filopodia formation, such as formins. I found that extracts depleted of Toca-1 binding partners no longer forms filopodia-like structures and subsequently optimised pull-down assays to identify Toca-1 binding partners by mass-spectrometry. I identified four formins, Diaph1, Diaph3, FHOD1 and INF2, and as well as the actin elongation factors and filopodia proteins, Ena and VASP. I further characterised these interactions and found that Toca-1 binds Ena and VASP via its SH3 domain. The interaction is direct and is strongly reduced if the proline-rich region in Ena is deleted. VASP was still able to bind without its proline rich region, suggesting there could be additional binding sites. I discovered that the binding of Ena and VASP was dependent on the clustering state of Toca-1, whilst the binding of the previously identified Toca-1 binding partner N-WASP was not. This further supports the importance of Toca-1 oligomerisation in actin polymerisation. I tested these interactions in the FLS system and found that increasing Toca-1 concentration leads to increased recruitment of N-WASP, as well as the novel binding partner Ena to the structures, whereas an increase in VASP was not observed. SH3-domain mediated interactions are required for Toca-1 recruitment to FLS, suggesting that its membrane and protein binding activities act cooperatively. I showed that unlike N-WASP, which promotes the formation of branched actin, Ena and VASP are not required for actin polymerisation on supported lipid bilayers, suggesting that they are redundant with other factors in the elongation step of FLS formation. Ena and VASP are known to be important for the formation of neuronal filopodia and so I began to further test the role of these interactions in a cellular context using a neuronal cell culture system. As well as recruiting protein binding partners, F-BAR family proteins are implicated in stabilising lipid microdomains and can induce the clustering of phosphoinositides. I investigated the role of Toca-1 in actin polymerisation on PI(4,5)P2-rich giant unilamellar vesicles (GUVs). Actin-rich tails formed on the GUVs only when excess Toca-1 was supplemented into the extracts, and I propose that this is due to lipid organisation by Toca-1. In summary, my work suggests a model in which Toca-1 clusters, stabilises the membrane lipids and recruits regulators of actin polymerisation, such as Ena. This mechanism could be used to link actin polymerisation to the membrane in cellular protrusions, such as filopodia.
39
Auger, Michèle. „Deuterium NMR and high-pressure FT-IR studies of membranes: Anesthetic-lipid interactions and molecular dynamics in lipid bilayers“. Thesis, University of Ottawa (Canada), 1990. http://hdl.handle.net/10393/5842.
Der volle Inhalt der QuelleAnnotation:
The interactions of the local anesthetic tetracaine with multilamellar dispersions of dimyristoylphosphatidylcholine (DMPC) containing cholesterol have been investigated by deuterium nuclear magnetic resonance ($\sp2$H NMR). $\sp2$H NMR spectra of tetracaine indicate that the location of the anesthetic in the cholesterol-containing DMPC bilayers differs from that in pure phosphatidylcholine bilayers, the anesthetic being located closer to the lipid-water interface in the former system. Moreover, the incorporation of the anesthetic into DMPC bilayers with or without cholesterol results in a reduction of the lipid order parameters both in the plateau and in the tail regions of the acyl chains, but does not significantly affect the cholesterol ordering. The interactions of tetracaine with the glycolipid 1,2-di-O-tetradecyl-3-O-($\beta$-D-glucopyranosyl)-sn-glycerol ($\beta$-DTGL) and with $\beta$-DTGL (20 mole%) in DMPC have also been investigated by $\sp2$H NMR. The stability of the lamellar structure of the pure glycolipid system is very sensitive to the presence of anesthetic while the interaction of tetracaine with the mixed glycolipid-phospholipid system does not trigger the formation of non-lamellar phases but leads to a slight reduction in molecular ordering. The location of tetracaine in different lipid bilayers and in nerves has been studied by high-pressure Fourier transform infrared (FT-IR) spectroscopy. The results reveal a correlation between the location of the anesthetic in model membranes and that in nerves. They also indicate that tetracaine is expelled by pressure from both model and nerve membranes, and that for model membrane systems, low pH or cholesterol will assist pressure in squeezing the anesthetic out of the bilayer. On the other hand, high-pressure FT-IR has also been used to study the effects of tetracaine on the structural and dynamic properties of lipids in model membrane systems. A combination of $\sp2$H spin-lattice relaxation and lineshape analysis has been used to demonstrate that a simple model involving two motions is sufficient to describe the spectral and relaxation features of the glycerol-labelled glycolipid $\beta$-DTGL. The lineshape and relaxation features of this lipid in the gel phase are best simulated using the three-site jump model with relative site populations of 0.46, 0.34 and 0.20, and a correlation time of 6.7 $\times$ 10$\sp{-10}$s. A second motion, namely rotation about the long axis of the molecule as a whole, is needed to account for the observed variation in the quadrupolar echo amplitude and the spectral lineshape over the temperature range of 25 to 60$\sp\circ$C. Similar results have been obtained for several phospholipid and glycolipid bilayers, which suggest that the glycerol backbone dynamics in all these systems can be described in terms of common fast internal motions and a slower whole molecule axial motion. Two-dimensional solid-state deuteron NMR spectroscopy has been used to confirm the presence of a slow whole molecule motion in the gel phase of the glycolipid $\beta$-DTGL at 35$\sp\circ$C, with an associated correlation time of the order of milliseconds. Comparison of the experimental and simulated two-dimensional ridge patterns suggest that a large angle jump about the long molecular axis can best account for the 2D exchange spectra of $\beta$-DTGL in the gel phase in comparison to small step Brownian diffusion. On the other hand, it is demonstrated that lateral diffusion over curved membrane surface of dipalmitoylphosphatidylcholine bilayers in the liquid-crystalline phase can be detected by 2D deuteron NMR, with an associated correlation time of the order of $\approx$100 ms.
40
Schütte, Ole Mathis. „Structure and dynamics of artificial lipid membranes containing the glycosphingolipid Gb3“. Doctoral thesis, Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2015. http://hdl.handle.net/11858/00-1735-0000-0023-960D-7.
Der volle Inhalt der Quelle
41
Gomes, Ligia Ferreira. „Permeabilidade de membranas ao ânion radical superóxido (O2-): estabelecimento de um método analítico para (O2- e estudo preliminar de permeabilidade em vesículas de anfifílico sintético“. Universidade de São Paulo, 1989. http://www.teses.usp.br/teses/disponiveis/9/9136/tde-27052008-134340/.
Der volle Inhalt der Quelle
42
Lazrak, Tarik. „Renforcateurs membranaires : etude structurale et evolution biochimique“. Université Louis Pasteur (Strasbourg) (1971-2008), 1987. http://www.theses.fr/1987STR13167.
Der volle Inhalt der Quelle
43
Sulaiman, Nurshahira. „Comparative proteomic analyses of outer membranes and outer membrane vesicles of Pasteurella multocida isolates recovered from different host species“. Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8639/.
Der volle Inhalt der QuelleAnnotation:
Pasteurella multocida is a Gram-negative bacterium that resides in the upper respiratory tract of domesticated animals. It is responsible for pneumonia in cattle, sheep and pigs, atrophic rhinitis in pigs, fowl cholera in poultry and haemorrhagic septicaemia of cattle and buffaloes. Different strains of P. multocida are associated with disease in different host species but little is known about the molecular basis of virulence and host-specificity in this pathogen. The outer membrane of P. multocida is at the interface between pathogen and host and it is highly likely that outer membrane proteins (OMPs) and lipopolysaccharide (LPS) are involved in disease pathogenesis and host-specificity. Outer membrane vesicles (OMVs) are derived from the outer membrane and there is increasing evidence of their involvement in disease pathogenesis. Hence, the present study aimed to compare the composition of OMPs and OMVs derived from different strains of P. multocida using proteomic approaches. Proteomic characterisation was carried out on the outer membranes of eight P. multocida isolates using gel-based and gel-free methods. A combination of gel-based and gel-free proteomic approaches identified a total of 67 OMPs associated with outer membrane biogenesis and integrity (11 proteins), transport and receptor activities (19 proteins), adherence (9 proteins), enzymatic activity (6 proteins) and unknown functions (22 proteins). Of these, 44 proteins were identified by both methods, 21 proteins were identified only by the gel-based method and two proteins were identified only by the gel-free approach. The study also characterised OMV production from the same P. multocida isolates and assessed the optimal OMV protein concentrations at different stage of growth. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis indicated that OMVs were enriched with OMPs and LPS. The OmpA protein was used as an outer membrane marker protein and its presence in OMVs was demonstrated by Western-blotting and immunogold-labelling. Proteomic analysis of the OMVs derived from the same eight P. multocida isolates was carried out by the gel-free approach in three biological replicates. A total of 200 proteins were identified and these included 58 OMPs, 43 periplasmic proteins, eight inner membrane proteins, 85 cytoplasmic proteins and six extracellular proteins. Interestingly, the number of proteins identified in the OMVs varied in different P. multocida isolates. Subsequently, OMPs identified in the outer membrane and OMV fractions were compared and the findings showed that OMPs associated with OM biogenesis and integrity were more likely to be present in the outer membrane, whereas OMPs associated with transport and receptor activities were highly enriched in the OMVs. These results highlight the potentially important role that OMVs of P. multocida play in disease pathogenesis and identified proteins for further evaluation as putative virulence factors and candidate vaccine antigens.
44
Blachon, Florence. „Membranes lipidiques supportées sur surfaces rugueuses : structure, dynamique et perspectives tribologiques“. Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1339/document.
Der volle Inhalt der QuelleAnnotation:
In vivo, les phopholipides interagissent avec des structures moléculaires rugueuses, telles des clusters ou fibrilles de protéines. Ce thème n’est pourtant que trop peu abordé dans la littérature scientifique, alors qu’il semblerait que la topologie de la surface sur laquelle repose ces molécules ou mêmes protéines influencent leurs propriétés. Notre projet s’est donc concentré sur les effets qu’un support accidenté pouvait soulever sur les bicouches lipidiques supportées (BLS).Dans un premier temps, nous avons étudié la mobilité de phopholipides déposés sur des supports plus ou moins rugueux par la méthode de recouvrement après photobleaching patterné (FRAPP pour Fluorescence Recovery After Patterned Photobleaching en anglais). Ces derniers ont été créés afin d’obtenir une large gamme de rugosité et caractérisés par Microscopie à Force Atomique.Nous sommes ensuite intéressés à la conformation d’une membrane sur ces substrats à l’aide de la technique non invasive de réflectivité de neutrons.Enfin, nous avons commencé à nous pencher sur les propriétés tribologiques des lipides lubrifiants nos surfaces rugueusesIn vivo lipid membranes interact with rough supramolecular structures such as protein clusters and fibrils However, this issue is not very developped in the state of art, while surface topology which interact with these molecules affects their properties. In this project, effects of rough surface on supported lipid bilayer (BLS) are investigated.First, lipid mobility are studied with the FRAPP method (Fluorescence Recovery After Photobleaching). BLS are deposited on rough supports which are characterized by AFM (Atomic Force Microscopy).Then, BLS structure on our rough surfaces are investigated by Neutron Reflectivity.Finally, first results on tribological properties of our systems are introduced
45
Chwastek, Grzegorz. „Interactions of FCHo2 with lipid membranes“. Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-129388.
Der volle Inhalt der QuelleAnnotation:
Endocytosis is one of the most fundamental mechanisms by which the cell communicates with its surrounding. Specific signals are transduced through the cell membrane by a complex interplay between proteins and lipids. Clathrin depended endocytosis is one of important signalling pathways which leads to budding of the plasmalemma and a formation of endosomes. The FCHo2 is an essential protein at the initial stage of the this process. In is a membrane binding protein containing BAR (BIN, Amphiphysin, Rvs) domain which is responsible for a membrane binding. Although numerous valuable work on BAR proteins was published recently, the mechanistic description of a BAR domain functionality is missing. In present work we applied in vitro systems in order to gain knowledge about molecular basis of the activity of the FCHo2 BAR domain. In our studies we used supported lipid bilayers (SLBs) and lipid monolayers as s model membrane system.
The experiments were carried out with a minimal number of components including the purified FCHo2 BAR domain. Using SLBs we showed that the BAR domain can bind to entirely flat bilayers. We also demonstrated that these interactions depend on the negatively charged lipid species incorporated in the membrane. We designed an assay which allows to quantify the membrane tubulation. We found out that the interaction of the FCHo2 BAR domain with the lipid membrane is concentration dependent. We showed that an area of the bilayer deformed by the protein depends on the amount of the used BAR domain.
In order to study the relation between the mobility of lipids and the activity of FCHo2 BAR domain we designed a small-volume monolayer trough. The design of this micro-chamber allows for the implementation of the light microscopy. We demonstrated that the measured lipid diffusion in the monolayer by our new approach is in agreement with literature data. We carried out fluorescence correlation spectroscopy (FCS) experiments at different density of lipids at the water-air interface.We showed that the FCHo2 BAR domain binding affinity is proportional to the mean molecular area (MMA). We additionally demonstrated that the increased protein binding is correlated with the higher lipid mobility in the monolayer.
Additionally, by curing out high-speed atomic force microscopy (hsAFM) we acquired the structural information about FCHo2 BAR domains orientation at the membrane with a high spatio-temporal resolution. Obtained data indicate the BAR domains interact witheach other by many different contact sites what results in a variety of protein orientations in a protein assemble.
46
Elias, Marianne. „Microfluidique pour manipuler et étudier des membranes biomimétiques“. Thesis, Toulouse 3, 2021. http://www.theses.fr/2021TOU30027.
Der volle Inhalt der QuelleAnnotation:
Les propriétés mécaniques de la membrane cellulaire contrôlent de nombreux processus biologiques. Les vésicules unilamellaires géantes (GUV) sont une approche facile pour reproduire la membrane cellulaire. L'aspiration par micropipettes est une technique bien connue utilisée pour caractériser leurs propriétés mécaniques, bien qu'elle implique une expérimentation de longue durée pour une mesure et une configuration complexe. Nous avons développé des plates-formes microfluidique visant à intégrer l'aspiration par micropipettes. Un avantage crucial de l'approche la plus avancée que nous avons mise en place est la flexibilité en termes de forme que nous pouvons fabriquer (en particulier forme de piège cylindrique). Cette approche permet également de multiplexer des micropipettes, offrant des mesures à haut débit, et enfin la possibilité de fabriquer les éléments composant la micropipette par centaines à la fois. Nous avons d'abord pu caractériser des compositions lipidiques simples telles que DOPC, POPC et Brain SM, dont les modules de courbure et d'étirement étaient en très bon accord avec les valeurs rapportées dans la littérature. Nous avons également caractérisé l'effet du cholestérol sur les membranes DOPC : le cholestérol augmentait le module d'étirement de la membrane DOPC mais n'affectait pas son module de courbure, rendant ainsi la membrane plus rigide. De plus, nous avons caractérisé la membrane DOPC contestée avec des nanoparticules de copolymères, généralement utilisées pour l'administration de médicaments. Ces nanoparticules ont induit un ramollissement de la membrane, qui pourrait être dû à l'effet de perméabilisation des NP sur la membrane, ou à leur insertion dans les membranes provoquant des défauts. Cette méthode étant polyvalente, en changeant la forme de la micropipette cylindrique en une section transversale permettant de piéger les GUV avec un écoulement résiduel autour d'elle, nous avons pu avoir une caractérisation préliminaire de l'effet de l'écoulement sur la fluidité des membranes. Enfin, nous avons adapté la taille de la micropipette afin de caractériser les propriétés viscoélastiques des sphéroïdes, agrégats de cellules cancéreuses 3D. Nous avons caractérisé la viscosité des cellules cancéreuses du pancréas et démontré qu'elle est indépendante de la taille des sphéroïdesThe mechanical properties of the cell's membrane control many biological processes. Giant Unilamellar vesicle (GUV) are an easy approach to reproduce cells membrane. Micropipette aspiration is a well-known technique used to characterize their mechanical properties, though it involves long time experimentation, and huge set up. Here we present a microfluidic platform that reproduce micropipette aspiration especially by its cylindrical trap form. The main advantage is the flexibility in terms of the shape we can fabricate, as well as the multiplexing micropipette, offering high throughput measurements and finally the ability to fabricate the elements composing the micropipette by hundreds at a time. We were able first to characterize simple lipid compositions such as DOPC, POPC and Brain SM, whose bending and stretching moduli are in very good agreement with the values reported in the literature. We also characterized the effect of cholesterol on DOPC membranes: cholesterol does increase the stretching modulus of DOPC membrane but does not affect its bending modulus, making therefore the membrane stiffer. Moreover, we characterized DOPC membrane challenged with co-polymers nanoparticles which are usually used for drug delivery and which showed a softening in the membrane which could be due to the permeation effect of the NP on the membrane. As this method is versatile, by changing the shape of the cylindrical micropipette to a cross section which allows the GUVs to be trapped with a residual flow around it, we were able to have a preliminary characterization of the effect of flow on the membranes' fluidity properties. Finally, we adapted the size of the micropipette in order to characterize the viscoelastic properties of spheroids made of cancer cells. We characterized the viscosity of pancreatic cancer cells and demonstrated that it is independent on the spheroids size
47
Aimon, Sophie. „Study of a voltage-gated ion channel reconstituted in Giant Unilamellar Vesicles“. Phd thesis, Université Pierre et Marie Curie - Paris VI, 2011. http://tel.archives-ouvertes.fr/tel-00736743.
Der volle Inhalt der QuelleAnnotation:
Il est difficile d'étudier in vivo le rôle de la membrane dans l'excitabilité des cellules car les paramètres pertinents (composition et état mécanique de la membrane, densité de canaux...) sont activement régulés par la cellule elle-même et donc difficilement ajustables expérimentalement. J'ai donc développé une méthode pour reconstituer un canal voltage-dépendant dans une membrane où ces paramètres peuvent être contrôlés. Pour cela j'ai exprimé, purifié et marqué KvAP, un canal potassique voltage-dépendant. J'ai ensuite adapté une méthode existante pour le reconstituer dans des Vésicules Unilamellaires Géantes (GUVs). J'ai mesuré la densité des canaux dans les GUVs grâce à la microscopie confocale. Des expériences d'électrophysiologie ont, de plus, montré que le canal reste fonctionnel après reconstitution. Ce système m'a permis d'étudier tout d'abord l'affinité du canal pour les membranes courbées. Pour cela, j'ai tiré des nanotubes de rayon contrôlé à partir de ces GUVs et j'ai mesuré la distribution du canal entre la vésicule et le tube par microscopie confocale. J'ai montré que le canal est enrichi dans le tube proportionnellement à sa courbure. Ce résultat est en accord avec une théorie basée sur l'élasticité de la membrane. Nous avons également étudié l'effet du confinement de la membrane sur la diffusion de KvAP. Par des expériences de suivi de particule unique, nous avons montré que le coefficient de diffusion le long du tube diminue d'un facteur 3 lorsque le rayon du tube décroît de 250 à 10 nm. Ce résultat est en accord avec le modèle hydrodynamique de Saffman et Delbrück appliqué à la géométrie cylindrique.
48
Satterfield, Laura Elizabeth. „Electrokinetic Properties of Lipid and Sarcoplasmic Reticulum Membranes in Aqueous Electrolyte and in the Presence of Lipophilic Ions“. PDXScholar, 2012. https://pdxscholar.library.pdx.edu/open_access_etds/78.
Der volle Inhalt der QuelleAnnotation:
The purpose of this study is the characterization of the membrane-water interfaces of both sarcoplasmic reticulum membrane (SR) and charged lipid bilayers under varied properties of the surrounding aqueous solution. In this work we studied the electrokinetic properties of liposomes and SR vesicles as well as the interaction of lipophilic ions with these membranes. The study of electrokinetic properties is based on the measurements of electrophoretic mobility of SR membrane vesicles and PC/PG liposomes. Electrophoretic mobility of SR vesicles was measured as a function of ionic strength for six pH values (pH 4.0, 4.7, 5.0, 6.0, 7.5, and 9.0). Electrophoretic mobility of single-layered and multi-layered PC/PG liposomes was measured at neutral pH as a function of ionic strength. For interpretation of electrophoretic mobility studies, SR vesicles (at pH 4, 7, and 9) and multi-layered and single-layered liposome sizes were determined using photoelectron microscopy. The study of the interaction of lipophilic ions with these membranes is based on (1) measurements of their partition coefficients described in terms of an ion partition model based on the Langmuir adsorption model and (2) electrophoretic mobility measurements of SR vesicles and PC liposomes in suspension with varied concentration of lipophilic ions. SR-water and PC-water partition coefficients were measured as a function of concentration for two anions tetraphenylborate (TePB-) and pentabromophenol (PBP-) and two cations (Imipramine+, and Clomipramine+). The anions belong to a class of pesticides and the cations are drugs once prescribed as anti-depressants. Partition into the SR membrane was shown to be significantly greater for all lipophilic ions except TePB-, which only showed this effect at the higher lipophilic ion range of the data. The PC-water partition coefficient was also measured for TePP+. Since the lipid bilayer of SR is not significantly different than that of PC liposomes, we believe the differences in partition are due to excess lipophilic ions being absorbed to the proteins of SR. The electrokinetics of charged PCPG liposomes, and PC liposomes with absorbed lipophilic ions could be understood in terms of the charge being located below their surface and screened by counter-ions inside the polar head-group region. We call this model the "permeable surface model". The assumptions of this model are that (1) the charge exists on a plane at a depth, d, below the surface of the liposome within the lipid head-group region and (2) small ions (Na+, K+, Cl-) are able to penetrate the lipid head-group region with a molar membrane-water partition coefficient of 0.4. Using this model we were able to obtain the depth of sorption of lipophilic ions in PC liposomes. We found values of 0.13 nm for TePB-, 0.5 nm for PBP-, 0.12 nm for Imipramine+, 0.17 nm for Clomipramine and 0.25 nm for TePP+. The depth of lipophilic ions in PC is a valuable quantity for the study of the effect of lipophilic ions on membrane function. For PCPG mobility we found the charged plane due to PG lipids was 0.2 nm for single-layered liposomes and 0.1 nm for multi-layered liposomes. This is consistent with the relative size of PC and PG head groups The dependence of SR mobility on pH was found to be directly correlated with the total charge of the A, P, and N domains of the Ca2+-ATPase as determined by the amino acid residues and their corresponding pKa values in water. We found that detached charged plane model, a new model developed in our group, could be fit to the mobility of SR as a function of ionic strength while other soft particle models failed. The assumptions of this model are that (1) the friction caused by protruding proteins on the surface of SR can be represented by a homogeneous retardation layer of thickness D and softness parameter λRL, and (2) the charge of the APN domain can be represented as a plane of charge embedded in the retardation layer at a distance s from the membrane surface. The best-fit values for λRL, and s were not consistent for different pH value studies. The detached charged plane model was unable to predict the mobility of SR vesicles in the presence of lipophilic ions if we assumed that the lipophilic ions were sorbing to the detached charged plane that represents the native charge of the APN domains of SR. At high lipophilic ion concentration the experimental mobilities consistently were greater in magnitude than the values predicted by the model. We concluded that there is significant absorption of lipophilic ions to the proteins in SR membrane, and that the lipophilic ion sorption sites are not the same as the detached plane of charge that represents the native charge of the APN domain.
49
Schweizer, Jakob. „Min-Protein Waves on Geometrically Structured Artificial Membranes“. Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-105880.
Der volle Inhalt der QuelleAnnotation:
Das stäbchenförmige Bakterium Escherichia coli teilt sich in zwei gleich große Tochterzellen. Dies ist nur möglich, wenn sich die Zelle in der Mitte teilt. Bei E. coli wird die Zellteilung durch den Zusammenschluss der FtsZ-Proteine an der Membran zum Z-Ring eingeleitet. Topologische Regulierung des Z-Ringes erfolgt durch räumlich-zeitliche Oszillationen von Min-Proteinen zwischen den beiden Zellpolen. MinC, MinD und MinE binden an und lösen sich von der Membran unter Hydrolyse von ATP und in antagonistischer Art und Weise, was zu einer alternierenden Ansammlung von MinC und MinD an den Zellpolen führt. Gemittelt über die Zeit ergibt sich somit ein MinD-Verteilungsprofil, das maximale Konzentration an den Zellpolen und ein Minimum in der Zellmitte aufweist. MinC bindet an MinD und folgt somit seiner Verteilung. Der Zusammenschluss von FtsZ-Proteinen wird durch MinC unterbunden, und somit kann sich der Z-ring nur an einer Position herausbilden, die ein Minimum an MinC aufweist - der Zellmitte. Das Min-system wurde in der Vergangenheit auch mit einem in-vitro-Ansatz untersucht, indem Min-Proteine in künstliche, aufliegende Lipiddoppelschichten (supported lipid bilayers, SLB) rekonstitutiert wurden. Dabei bildeten die Min-Proteine kein oszillierendes Muster aus, sondern organisierten sich vielmehr in parallelen und propagierenden Wellen (Loose, 2008, Science, 320). In diesen in-vitro-Experimenten war das Membransubstrat wesentlich größer als die Wellenlänge der Min-Proteinwellen. In vivo hingegen ist die Länge der Zelle in der gleichen Größenordnung wie die charakteristische Länge des Oszillationsmusters der Min-Proteine. Daher war es das Ziel dieser Arbeit, den Einfluß einer beschränkten Fläche und geometrischer Formgebung der künstlichen Lipiddoppelschichten auf die Wellenpropagation der Min-Protein zu untersuchen. Flächige Beschränkung künstlicher Membranen erfolgte durch Mikrostrukturtechnologie. Deckglässchen wurden mit einer Goldschicht und mikroskopischen Aussparungen unterschiedlicher geometrischer Formen strukturiert. Funktionale SLBs bildeten sich nur auf Glasflächen ohne Goldbeschichtung aus. Nach der Rekonstitution der Min-Proteine, organisierten sich diese auf den Membranstücken in parallele Wellen. Dabei bestimmte die flächige Beschränkung der künstlichen Membranen die Ausbreitungsrichtung der Min-Proteinwellen. Min-Proteinwellen konnten entlang gekrümmter Membranstreifen, in Ring- und sogar in Slalomstrukturen geleitet werden. In geraden, länglichen Strukturen richteten sich die Wellen entlang der längsten Achse aus. Kopplung von Proteinwellen auf räumlich getrennten Membranstücken in Abhängigkeit des Abstandes und des sogenannten Molecular Crowdings in der wässrigen Lösung konnte ebenfalls beobachtet werden. Diese Kopplung ist ein Indiz für inhomogene Proteinverteilungen in der Lösung oberhalb der Membran. Desweiteren konnten Min-Proteinwellen auch in diversen dreidimensionalen künstlichen Membranen rekonstitituiert werden. Im Wildtyp von E. coli ähneln die Min-Proteindynamiken der einer Oszillation mit einer charakteristischen Länge von 5 µm. Auf SLBs, bilden Min-Proteine Wellen mit einer Wellenlänge aus, die ca. zehnmal größer ist als in vivo. Dieser Unterschied zwischen der in-vivo- und der in-vitro-Welt wurde untersucht und diskutiert. In vitro konnte die Wellenlänge um 50 % durch Erhöhung des Molecular Crowding in der Lösung sowie um 33 % durch Temperaturerhöhung verkleinert werden. Das oszillierende Muster könnte dahingegen eine Folge der Kompartimentierung sein. Erste Versuche, das Min-System in geschlossene Membrankompartimente zu rekonstitutieren, wurden getestetEscherichia coli, a rod-like bacterium, divides by binary fission. Cell division into two daughter cells of equal size requires that fission takes place at a midcell position. In E. coli, cell division is initiated by assembly of the FtsZ-proteins at the inner membrane to the Z-ring. Topological regulation of the Z-ring is achieved by spatiotemporal pole-to-pole oscillations of Min-proteins. MinC, MinD and MinE bind to and detach from - under hydrolysis of ATP - the membrane in an antagonistic manner leading to an alternating accumulation of MinC and MinD at the cell poles. Averaged over time, the distribution profile of MinD exhibits maximal concentration at the cell poles and a minimum at the cell center. MinC binds to MinD and thus follows its distribution. FtsZ assembly is inhibited by MinC and therefore the Z-ring can only form at a cell position low in MinC - at the cell center. In the past, the Min-system was also investigated in an in vitro approach by reconstitution of Min-proteins into a supported lipid bilayer (SLB). Here, Min-proteins did not self-organize into an oscillatory pattern but into parallel and propagating waves (Loose, 2008, Science, 320). In this in vitro assay, the membrane substrate was infinitely large compared to the wavelength. However, in vivo, the cell length is on the same order of magnitude as the respective length scale of the oscillatory pattern of Min-proteins. Therefore, we wished to investigate the effect of lateral confinement and geometric structuring of artificial lipid bilayers on the Min-protein wave propagation. Lateral confinement of artificial membranes was achieved by microfabrication technology. Glass slides were patterned by a gold coating with microscopic windows of different geometries, and functional SLBs were only formed on uncoated areas. Upon reconstitution, Min-proteins organized into parallel waves on the geometric membrane patches. Confinement of the artificial membranes determined the direction of propagation of Min-protein waves. Min-protein waves could be guided along curved membrane stripes, in rings and even along slalom-geometries. In elongated membrane structures, the protein waves always propagate along the longest axis. Coupling of protein waves across spatially separated membrane patches was observed, dependent on gap size and level of molecular crowding of the aqueous media above the bilayer. This indicates the existence of an inhomogeneous and dynamic protein gradient in the solution above the membrane. Furthermore, reconstitution of Min-protein waves in various three-dimensional artificial membranes was achieved. In wild-type E. coli, Min-protein dynamics resemble that of an oscillation with a characteristic length scale of 5 µm. On supported lipid bilayers, Min-proteins self-organize into waves with a wavelength approximately 10-fold larger than in vivo. These discrepancies between the in vivo and in vitro world were investigated and discussed. In vitro, the wavelength could be decreased by a factor of 50 % by increase of the molecular crowding in solution and by 33 % through temperature increase. The oscillatory pattern is thought to be a consequence of compartmentalization and first attempts to encapsulate the Min-system in closed bilayer compartments are presented
50
Ding, Wei. „Molecular dynamics simulation of biomembrane systems“. Thesis, Queen Mary, University of London, 2018. http://qmro.qmul.ac.uk/xmlui/handle/123456789/36217.
Der volle Inhalt der QuelleAnnotation:
The fundamental structure of all biological membranes is the lipid bilayer. At- tributed to the multifaceted features of lipids and its dynamical interaction with other membrane-integrated molecules, the lipid bilayer is involved in a variety of physiological phenomena such as transmembrane transportation, cellular signalling transduction, energy storage, etc. Due to the nanoscale but high complexity of the lipid bilayer system, experimental investigation into many important processes at the molecular level is still challenging. Molecular dynamics (MD) simulation has been emerging as a powerful tool to study the lipid membrane at the nanoscale. Utilizing atomistic MD, we have quantitatively investigated the effect of lamellar and nonlamellar lipid composition changes on a series of important bilayer properties, and how membranes behave when exposed to a high-pressure environment. A series of membrane properties such as lateral pressure and dipole potential pro les are quanti ed. Results suggest the hypothesis that compositional changes, involving both lipid heads and tails, modulate crucial mechanical and electrical features of the lipid bilayer, so that a range of biological phenomena, such as the permeation through the membrane and conformational equilibria of membrane proteins, may be regulated. Furthermore, water also plays an essential role in the biomembrane system. To balance accuracy and efficiency in simulations, a coarse-grained ELBA water model was developed. Here, the ELBA water model is stress tested in terms of temperature- and pressure-related properties, as well as hydrating properties. Results show that the accuracy of the ELBA model is almost as good as conventional atomistic water models, while the computational efficiency is increased substantially.