Spontaneous incorporation of bacteriorhodopsin into large preformed vesicles.
Bacteriorhodopsin, either as purple membrane sheets or as detergent-solubilized protein, was found to incorporate spontaneously into both large unilamellar vesicles (LUVs) and sized multilamellar vesicles (MLVs) under either gel-phase or liquid-phase conditions. These results were obtained with LUVs of various lipid compositions, including dimyristoylphosphatidylcholine (DMPC), DMPC and cholesterol, dioleoylphosphatidylcholine (DOPC), and DOPC and cholesterol. The lipid to protein (L/P) ratio of all proteoliposomes arising from these preformed vesicles continually increased in the presence of protein-free vesicles. Under fluid-phase conditions, the mixing of LUVs of DMPC with proteoliposomes showed vesicle growth independent of lipid concentration, suggesting that growth was due to lipid transfer. However, under gel-phase conditions a more rapid, concentration-dependent increase in the L/P ratio of the proteoliposome was observed, suggesting that growth occurred by a mechanism other than lipid transfer from vesicles to proteoliposomes. The use of the proteoliposome as an artificial lipid-protein membrane model is discussed.
Scotto
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AW
Department of Medicine, Cornell University Medical College, New York, New York 10021.
Gompper
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ME
D001426:Bacterial Proteins / Q000378:metabolism*; D001436:Bacteriorhodopsins / Q000378:metabolism*; D002784:Cholesterol; D004134:Dimyristoylphosphatidylcholine; D008081:Liposomes / Q000378:metabolism*; D010713:Phosphatidylcholines
D001426:Bacterial Proteins; D008081:Liposomes; D010713:Phosphatidylcholines; D001436:Bacteriorhodopsins; D002784:Cholesterol; C017251:1,2-oleoylphosphatidylcholine; D004134:Dimyristoylphosphatidylcholine