Phase equilibria of membrane lipids for Acholeplasma laidlawii: importance of a single lipid forming nonlamellar phases

Abstract

A basis for the reorganization of the bilayer structure in biological membranes is the different aggregate structures formed by lipids in water. The phase equilibria of all individual lipids and several in vivo polar lipid mixtures from acyl chain modified membranes of Acholeplasma laidlawii were investigated with different NMR techniques. All dioleoyl (DO) polar lipids, except monoglucosyldiglyceride (MGDG), form lamellar liquid crystalline (L alpha) phases only. The phase diagram of DOMGDG reveals reversed cubic (III), reversed hexagonal (HII), and L alpha phases. In mixtures of DOMGDG and dioleoyldiglycosyldiglyceride (DODGDG), the formation of an III (or HII) phase is enhanced by DOMGDG and low hydration or high temperatures. For in vivo mixtures of all polar DO lipids, a transition from an L alpha to an III phase is promoted by low hydration or high temperatures (50 degrees C). The phospholipids are incorporated in this III phase. Likewise, III and HII phases are formed at similar temperatures in a series of in vivo mixtures with different extents of acyl chain unsaturation. However, their melting temperatures (Tm) vary in an expected manner. All cubic and hexagonal phases, except the III phase with DOMGDG, exist in equilibrium with excess water. The maximum hydration of MGDG and DGDG is similar and increases with acyl chain unsaturation but is substantially lower than that for, e.g., phosphatidylcholine. The translational diffusion of the lipids in the cubic phases is rapid, implying bicontinuous structures. However, their appearances in freeze-fracture electron microscope pictures are different. The III phase of DOMGDG belongs to the Ia3d space group.(ABSTRACT TRUNCATED AT 250 WORDS)

Wild-type Escherichia coli Cells Regulate the Membrane Lipid Composition in a “Window” between Gel and Non-lamellar Structures

“…The line shape of the 31 P NMR signal depends on the symmetry of the phospholipid aggregates (Brentel et al, 1987;Cullis and de Kruijff, 1976;Lindblom et al, 1986;McLaughlin et al, 1975). A lamellar liquid crystalline (L ␣ ) phase gives rise to a spectrum with a high field peak and a low field shoulder.…”

“…The two theories for lipid self-assembly constitute decisive bases for the model we have presented concerning the regulation of the membrane lipid composition in A. laidlawii strain A-EF22 (Lindblom et al, 1986Rilfors et al, 1993;Wieslander et al, 1980). The organism can synthesize only saturated fatty acids .…”

“…The two most important conclusions that have been drawn from a combination of biochemical and physico-chemical studies of the A. laidlawii membrane lipids are: 1) the proportions of all the lipids are carefully balanced in relation to the prevailing growth conditions 2 Wieslander et al, 1995). The consequence of this balanced lipid synthesis is that the tendency of total lipid extracts to form reversed nonlamellar phases is maintained within narrow limits (Lindblom et al, 1986;Lindblom and Rilfors, 1989;Rilfors et al, 1994;Ö sterberg et al, 1995); and 2) total lipid extracts have an ability to form reversed non-bilayer aggregates and non-lamellar phases under conditions that are relatively close to the physiological ones (Lindblom et al, 1986;Rilfors et al, 1994;Ö sterberg et al, 1995).…”

“…The organism can be grown under conditions where the regulatory changes occur predominantly in the polar head group structures. The conclusion has been drawn that the cells strive to maintain a certain balance between the lipids constituting a bilayer structure and those forming reversed non-lamellar structures (Lindblom et al, 1986Rilfors et al, 1993Rilfors et al, , 1994Ö sterberg et al, 1995). A. laidlawii strain A-EF22 synthesizes eight membrane lipids of which three are able to form non-lamellar phases: monoglucosyldiacylglycerol (MGlcDAG), 1 and the monoacylated derivatives of MGlcDAG and diglucosyldiacylglycerol (DGlcDAG) 2 Rilfors et al, 1993).…”

Interactions of Cyclic AMP and Its Dibutyryl Analogue with a Lipid Layer in the Aqueous Mixtures of Monoolein Preparation and Dioleoyl Phosphatidylcholine as Probed by X-Ray Diffraction and Raman Spectroscopy

“…Firstly, the Pn3m cubic phase of MO can coexist with bulk water. Secondly, there is a good ground to claim that nonlamellar (e.g., bicontinuous cubic, reversed hexagonal) structures of lipids perform a number of biological roles [4][5][6][7][8].…”