Reconstitution and electron paramagnetic resonance-spectroscopic characterization of glycophorin containing phospholipid vesicles

Glycophorin A containing dimyristoylphosphatidylcholine vesicles has been reconstituted by reverse-phase evaporation, detergent dialysis, freeze and thaw cycles as well as by rehydration of a lipid-protein-film. The availability of each method has been tested. Reproducible results with a highly purified protein were only obtained by the reverse phase evaporation and the detergent dialysis techniques. The lipid-protein interaction was studied by electron spin resonance experiments using spin labeled phosphatidylcholine (PC-SL), phosphatidylglycerol (PG-SL) and phosphatidylethanolamine (PE-SL) as probe molecules. With PC-SL we observed protein-induced motionally restricted lipid, which is stable up to 40°C in DMPC-membranes. This rigidification in the fluid phase was already obtained at very low glycophorin content. It is interpretable with an elastic force model, where the membrane distortion is induced by a mismatch of lipid and protein hydrophobic thickness. Negatively charged PG-SL undergoes an additional electrostatic interaction leading to a preferential binding over PC-SL. With PE-SL we failed to observe motionally restricted lipid. However, the probe becomes diffusionally restricted in fluid bilayer membranes probably by hydrogen bond formation.