Lipid-protein stoichiometries in a crystalline biological membrane: NMR quantitative analysis of the lipid extract of the purple membrane

Abstract

The lipid/protein stoichiometries of a naturally crystalline biological membrane, the purple membrane (PM) of Halobacterium salinarum , have been obtained by a combination of 31 P-and 1 H-NMR analyses of the lipid extract. In total, 10 lipid molecules per retinal were found to be present in the PM lipid extract: 2-3 molecules of phosphatidylglycerophosphate methyl ester (PGP-Me), 3 of glycolipid sulfate, 1 of phosphatidylglycerol, 1 of archaeal glycocardiolipin (GlyC), 2 of squalene plus minor amounts of phosphatidylglycerosulfate (PGS) and bisphosphatidylglycerol (archaeal cardiolipin) (BPG) and a negligible amount of vitamin MK8. The novel data of the present study are necessary to identify the lipids in the electron density map, and to shed light on the structural relationships of the lipid and protein components of the PM. -Corcelli, A., V. M. T. Lattanzio, G. Mascolo, P. Papadia, and F. Fanizzi. Lipidprotein stoichiometries in a crystalline biological membrane: NMR quantitative analysis of the lipid extract of the purple membrane.

How lipids and proteins interact in a membrane: a molecular approach

“…14 The crystal structure of bacteriorhodopsin is unique in including a large number of lipid molecules, 26,27 these molecules being retained presumably because of the special properties of bacteriorhodopsin: bacteriorhodopsin occurs as a trimer in the quasi-crystalline purple membrane of the bacterium Halobacterium salinarum, where the molar ratio of lipid to protein is unusually low, with about 30 lipid molecules per bacteriorhodopsin trimer. 28 Some of these lipid molecules can be seen in the crystal structure (Fig. 1) forming a shell or annulus around the protein; in the native membrane the whole of the hydrophobic surface of the trimer would, of course, be covered by lipid molecules.…”

Average Conformation of Branched Chain Lipid PGP-Me That Accounts for the Thermal Stability and High-Salinity Resistance of Archaeal Membranes

“…10−15 The bilayers of PM mainly consist of acidic polar lipids represented by phosphatidyl glycerophosphate methyl ester (PGP-Me, 1 in Figure 1). 16,17 PGP-Me has two characteristic structural features: an acidic bisphosphate headgroup and methyl-branched alkyl chains, which bind to the glycerol moiety via ether linkages in contrast to the ester linkages of usual eukaryotic lipids. Previous studies have clearly revealed that PGP-Me plays a crucial role in the structural and functional conservation of bR as a proton pump in reconstituted membranes.…”

“…One of the characteristic features of these archaea is their membrane lipids, which usually possess phytanyl or methyl-branching hydrocarbon chains. − One species in this genus, Halobacterium salinarium , is well-known to produce bacteriorhodopsin (bR), which is a proton-pumping protein present in the purple membrane (PM). − The surrounding lipids are thought to significantly contribute to the biological features of bR, including its excellent thermal stability and high-salinity resistance. − The bilayers of PM mainly consist of acidic polar lipids represented by phosphatidyl glycerophosphate methyl ester (PGP-Me, 1 in Figure ). , PGP-Me has two characteristic structural features: an acidic bisphosphate headgroup and methyl-branched alkyl chains, which bind to the glycerol moiety via ether linkages in contrast to the ester linkages of usual eukaryotic lipids. Previous studies have clearly revealed that PGP-Me plays a crucial role in the structural and functional conservation of bR as a proton pump in reconstituted membranes. , In addition, PGP-Me is known to significantly contribute to the high-salinity resistance of PM .…”

Stereoselective synthesis of the head group of archaeal phospholipid PGP-Me to investigate bacteriorhodopsin–lipid interactions

“…Phosphatidylglycerophosphate methyl ester (PGP-Me, 1 in Fig. 1), which is the major constituent of PM lipids, 19,20 Fig. 1 Chemical structures of compounds 1-3 with two phosphate esters a and b.…”