Modulation of Folding and Assembly of the Membrane Protein Bacteriorhodopsin by Intermolecular Forces within the Lipid Bilayer
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- 作者：A. Rachael Curran ; Richard H. Templer ; and Paula J. Booth
- 刊名：Biochemistry
- 出版年：1999
- 出版时间：July 20, 1999
- 年：1999
- 卷：38
- 期：29
- 页码：9328 - 9336
- 全文大小：94K
- 年卷期：v.38,no.29(July 20, 1999)
- ISSN：1520-4995
文摘
Three different lipid systems have been developed to investigate the effect of physicochemicalforces within the lipid bilayer on the folding of the integral membrane protein bacteriorhodopsin. Eachsystem consists of lipid vesicles containing two lipid species, one with phosphatidylcholine and the otherwith phosphatidylethanolamine headgroups, but the same hydrocarbon chains: either L-
-1,2-dioleoyl,L--1,2-dipalmitoleoyl, or L--1,2-dimyristoyl. Increasing the mole fraction of the phosphatidylethanolaminelipid increases the desire of each monolayer leaflet in the bilayer to curve toward water. This increasesthe torque tension of such monolayers, when they are constrained to remain flat in the vesicle bilayer.Consequently, the lateral pressure in the hydrocarbon chain region increases, and we have used excimerfluorescence from pyrene-labeled phosphatidylcholine lipids to probe these pressure changes. We showthat bacteriorhodopsin regenerates to about 95% yield in vesicles of 100% phosphatidylcholine. Theregeneration yield decreases as the mole fraction of the corresponding phosphatidylethanolamine componentis increased. The decrease in yield correlates with the increase in lateral pressure which the lipid chainsexert on the refolding protein. We suggest that the increase in lipid chain pressure either hinders insertionof the denatured state of bacterioopsin into the bilayer or slows a folding step within the bilayer, to theextent that an intermediate involved in bacteriorhodopsin regeneration is effectively trapped.
-1,2-dioleoyl,L--1,2-dipalmitoleoyl, or L--1,2-dimyristoyl. Increasing the mole fraction of the phosphatidylethanolaminelipid increases the desire of each monolayer leaflet in the bilayer to curve toward water. This increasesthe torque tension of such monolayers, when they are constrained to remain flat in the vesicle bilayer.Consequently, the lateral pressure in the hydrocarbon chain region increases, and we have used excimerfluorescence from pyrene-labeled phosphatidylcholine lipids to probe these pressure changes. We showthat bacteriorhodopsin regenerates to about 95% yield in vesicles of 100% phosphatidylcholine. Theregeneration yield decreases as the mole fraction of the corresponding phosphatidylethanolamine componentis increased. The decrease in yield correlates with the increase in lateral pressure which the lipid chainsexert on the refolding protein. We suggest that the increase in lipid chain pressure either hinders insertionof the denatured state of bacterioopsin into the bilayer or slows a folding step within the bilayer, to theextent that an intermediate involved in bacteriorhodopsin regeneration is effectively trapped.