Protéine membranaire

Résumé

Les protéines membranaires constituent l'une des trois principales classes de protéines à côté des protéines fibreuses et des protéines globulaires. Suivant le type de cellule et d'organite cellulaire, une membrane peut contenir des centaines de protéines différentes. Chaque protéine membranaire possède une orientation définie par rapport au cytoplasme : c'est pourquoi les propriétés des faces de la membrane sont très différentes. On parle de l’asymétrie de la membrane. Dans la membrane plasmique, par exemple, les portions des protéines membranaires qui interagissent avec d'autres cellules ou avec des substances émergent dans l'espace extracellulaire, tandis que les portions qui interagissent avec des molécules cytoplasmiques sortent dans le cytosol. On peut grouper les protéines membranaires en trois classes différentes qui se distinguent par l'intimité de leurs rapports avec la bicouche lipidique. On distingue les protéines intrinsèques, intégrées dans la membrane, et extrinsèques,

Source officielle

https://fr.wikipedia.org/wiki/Prot%C3%A9ine_membranaire

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redresse=1.36|vignette|Représentation d'une protéine, ici deux sous-unités d'une molécule d'hémoglobine. On observe les représentées en couleur, ainsi que deux des quatre molécules d'hème, qui sont l

upright=1.33|vignette|Représentation d'une bicouche lipidique constituée de phosphoglycérides. Une bicouche lipidique, ou double couche lipidique, est une fine membrane polaire constituée de deux feu

La membrane plasmique, également appelée membrane cellulaire, membrane cytoplasmique, voire plasmalemme, est une membrane biologique séparant l'intérieur d'une cellule, appelé cytoplasme, de son envir

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Supported lipid monolayers for the investigation of specific interactions between proteins and ligands

In this work, the specific and nonspecific binding of proteins to planar surfaces was investigated. The surfaces were first modified by the spontaneous adsorption of a number of synthesized 1,2-diacyl-sn-glycero-3-phosphatidylcholine lipids with different ω-mercapto fatty acids. The influence of packing density, order, fluidity, and mobility of the head groups of these supported thiolipid monolayers on the nonspecific adsorption of proteins was systematically investigated. Nonspecific binding of fibrinogen, IgG, BSA, and rabbit serum to such surfaces was monitored on-line by surface plasmon resonance spectroscopy (SPR) and was found to be exceptionally low. Characterization of the supported thiolipid monolayers by grazing incidence infrared spectroscopy, wetting, impedance spectroscopy, calorimetry, and SPR indicates that protein adsorption is influenced by the nature of the fatty acids and suggests that besides the molecular structure of the layer-forming molecules, other supramolecular aspects such as flexibility of the immobilized lipid layer or protrusion of the lipid head groups play a role. These investigations point the way for the construction of even more highly protein repellent surfaces with potential technical applications in the medical (implants) and diagnostic fields (biosensors). To investigate specific protein-surface interactions, acetylcholine containing ligand molecules of the general molecular structure HS(CH2)15(CO)O(CH2CH2O)nCH2(CO)OCH2CH2N+(CH3)3 X- (n = 4, 6, 13) were synthesized. They allow acetylcholine, the natural agonist of the acetylcholine receptor, to be covalently immobilized on a surface. Mixed layers of thiolipids and ligand molecules were formed by self-assembly on planar gold substrates and specific interactions between the immobilized acetylcholine and the nicotinic acetylcholine receptor (nAchR) from Torpedo Californica have were investigated on-line by SPR. Though it seems that the receptor binds specifically, bound receptor could be only partially displaced from the surface by excess free ligand. However, further improvement of the sensor surfaces will surely provide in the future a powerful tool for the investigation of membrane proteins and transmembrane communication.

EPFL1997

Chargement

Investigation of peptides and membrane proteins at interfaces using Fourier transform infrared spectroscopy

Per Rigler

EPFL2002

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G Protein coupled receptors (GPCRs) constitute an abundant family of membrane proteins which play a central role in cellular signaling and are important targets for modern medicine. Despite intensive research, central questions of the molecular mechanism of GPCR mediated signal transduction remain unresolved. This thesis concerns α1b-adrenergic receptor (α1b-AR) as a prototypic GPCR. The question whether ARs form homo- or hetero-oligomers was investigated using fluorescence resonance energy transfer (FRET). An important finding was that both α1a and α1b-AR subtypes form homo-oligomers. Also hetero-oligomers have been observed between the α1b- and the α1a-AR subtypes, but not with less related receptors. Another interesting finding concerns α1-AR co-internalization which correlates with the ability of the receptor to hetero-oligomerize. Investigating particular processes in living cells is often complicated by the complex cellular environment. Here we have developed a rather simple approach to study transmembrane signaling by using supported cell membrane sheets. They were prepared by pressing a glass coverslip on the apical part of cultured cells, ripping off large regions of the native plasma membrane. For the α1b-AR we still could observe ligand binding to such sheets, indicating that GPCR functionality was at least partly conserved. Due to the absence of cytosolic autofluorescence of the cells, supported membrane sheets were also found to be suited for single-molecule microscopy. Because both leaflets of the supported membranes remained fluid, it was possible to follow the diffusion of certain membrane proteins. For example using fluorescence recovery after photobleaching (FRAP) and single-molecule microscopy, we investigated how G proteins diffused along the membrane and compartmentalized. The predominant role of lipid anchors in G protein localization was highlighted by measuring the diffusion of two Gαq proteins fused with citrine at two different positions and citrine based constructs designed to mimic the monomeric and the trimeric form of a G protein. Finally, first results were obtained showing the feasibility to form supported cell membrane sheets on microstructured devices consisting of a planar silicon support perforated with arrays of holes. This geometry provides a full accessibility to both intra- and extracellular sides of the bilayer. This concept could potentially be applied for the development of chip-based screening assays.

EPFL2005

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EPFL2005

Supported lipid monolayers for the investigation of specific interactions between proteins and ligands

EPFL1997