The Regulation of Bilayer Stability in Bacteria

Abstract

The membranes of prokaryotic and eukaryotic cells contain mixtures of amphipathic lipids. When isolated, the major lipids can form different phase structures upon hydration at physiological temperatures. As discussed in other lectures in this volume (de Kruijff, Op den Kamp), the structures of lipid aggregates are related to the generalized shapes of the molecules. Bilayer-forming lipids (type II) have roughly cylindrical shapes whereas H_II phase lipids (type III) have a cone shape in which the area swept out by the motion of the hydrocarbon chains is larger than that occupied by the polar head groups. Hydration, charge repulsion, and hydrogen bonding, can affect the cross-sectional areas of the polar regions, and temperature and chain unsaturation influence the volumes occupied by the hydrocarbon chains (Rilfors et al., 1984; Cullis & Hope, 1985).Among the type II lipids found in prokaryotes are phosphatidylcholine (PC), phosphatidylglycerol (PG), phosphatidylserine (PS), cardiolipin (CL), and diglycosyldiacylglycerols. Among type III lipids are unsaturated species of phosphatidylethanolamine (PE), plasmenylethanolamine (PlaE) and monoglycosyldiacylglycerols (Goldfine, 1982). Lipids that aggregate to form micelles (Type I), for example lyso-phosphoglycerides, are rarely found in large amounts.

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Research in the author’s laboratory was supported by a research grant from the U.S. Public Health Service, National Institute of Allergy and Infectious Disease, #AI-08903.