Reconstitution of Bacteriorhodopsin Vesicles with Halobacterium halobium Lipids

Reconstitution of bacteriorhodopsin into vesicles has been studied using individual and defined mixtures of fractionated Halobacterium halobium polar lipids. The lipids varied greatly in their ability to form vesicles that translocated protons and showed stimulation by valinomycin. Thus, phosphatidylglycerol phosphate gave mainly lipid-protein aggregates, while glycolipid sulfate gave mainly functional vesicles. Addition of glycolipid sulfate to phosphatidylglycerol phosphate promoted vesicle formation. Reconstitutions performed with different combinations of the purified lipids showed: 1) that vesicles with maximal proton pumping are obtained with a mixture of phosphatidylglycerol phosphate and glycolipid sulfate at a ratio close to that found in the purple membrane; 2) increasing the concentration of glycolipid sulfate in vesicles increases the stimulation of proton translocation by valinomycin; 3) phosphatidylglycerol sulfate cannot replace glycolipid sulfate or phosphatidylglycerol phosphate; and 4) vesicles containing sulfated polar lipids only are inferior to those in which lipid combinations containing phosphatidylglycerol phosphate are used.