Glycophorin A in phosphatidylcholine bilayer membranes

Abstract

Glycophorin A is one of the major integral proteins in erythrocyte membranes. We will report on the reconstitution of Glycophorin A into artificial phosphatidylcholine membranes (DMPC) in the concentration range between O,i and i0 mol %o proteins. The influence of the protein on the structure and the dynamics of the lipid matrix has been investigated by the following techniques: i) Electron paramagnetic resonance (EPR) and calorimetry (DTA).We observed a slight shift of the main phase transition temperature of about 3o. The order degree of the lipid fatty acid chains shows a minimum at a molecular content of 0,7 %o Glycophorin. 2) Fluorescence recovery after photobleaching (FRAP) and excimer techniqueThe lateral mobility of Glycophorin and lipid analoges is determined. Zt shows a quite complex dependence from the protein/lipid molar ratio. The "pretransition" of the lipid matrix is clearly more important for the lateral diffusion of Glycophorin A than the main transition. For comparison excimer-technique was applied to determine the lipid mobility by using the lipid analogue pyren lecithin. 3) Energy transferGlycophorin and lipids were labelled with two fluorophores. Energy transfer is measured in different experiments between Glycophorins as well as protein to lipid transfer. Lipid to lipid transfer experiments serve as standard of statistical distribution. At 0,8 %0 is a local maximum of protein-protein ET and a minimum of lipid protein ET. 4) ElectronmicroscopyThe experiments yield information about the surface texture of individual lipid bilayers. Glycophorin seems to be preferentially located in defect lines and -1/2 defects of the P~'phase. Higher concentration of protein leads to a suppression of the P~'phase, but by lowering the temperature the PB'phase reappears. Above 1%0 and at low temperatures particles are observed in the defects of the PB' phase. Glycophorin blocks the pretransition to the L~'phase. We can differenciate three regions of concentration O -O,8 , 0,8 -4 , 4 -i0 mol %0. 0,8 ~o is a distinguished point. The interpretation will be given in terms of aggregational and conformational changes of the glycophorin molecules, carbohydrate-lipid interactions, defect of the lipid matrix, long ranging proteinprotein lipid mediated interactions.

Oligosaccharide Behavior of Complex Natural Glycosphingolipids in Multicomponent Model Membranes

“…Glycophorin was chosen in the present work as an example of a membrane-spanning species with extensive carbohydrate (Marchesi et al, 1976). Bilayers containing glycophorin have been extensively characterized by us and other workers (Ketis & Grant, 1980;Ruppel et al, 1982; Grant & Peters 1984; MacDonald & Pink, 1987), and it is known to distribute uniformly as small oligomers in such systems. Glycophorin A is a 30 kDa integral membrane protein that contains 16 (-)-charged oligosaccharide chains (Vítala & Jamefelt, 1985).…”

On defects in different phases of two-dimensional lipid bilayers

“…One observes + 1 disclinations with point-like cores, but -1 disclinations always exhibit lines like cores. c) Addition of 0.2 %0 glycophorine A (for a general information about this protein and its interaction with lipids see for example [23]). The protein is preferentially accumulated in the point and line defects.…”

Characterization of the permeability increase induced by the incorporation of glycophorin in phosphatidylcholine vesicles

“…Since these packing defects result in a permeability increase for much smaller solutes [ 151 we favour the idea that the permeation of solutes through the glycophorin-DOPC bilayer occurs through channels, formed by glycophorin aggregates. Recently it was suggested that the sugar-containing externally located part of glycophorin may interact with the phospholipid bilayer [22]. Possibly this interaction may play a role in the formation of the permeation pathway, present in the glycophorin-DOPC vesicles.…”