Order and dynamics in mixtures of membrane glucolipids from Acholeplasma laidlawii studied by deuterium NMR

Abstract

The two dominant glucolipids in Acholeplasma laidlawii, viz., 1,2-diacyl-3-O-(alpha-D-glucopyranosyl)-sn-glycerol (MGlcDG) and 1,2-diacyl-3-O-[alpha-D-glucopyranosyl-(1----2)-O-alpha-D-glucopyranosyl ]- sn-glycerol (DGlcDG), have markedly different phase behavior. MGlcDG has an ability to form nonlamellar phases, whereas DGlcDG only forms lamellar phases. For maintenance of a stable lipid bilayer, the polar headgroup composition in A. laidlawii is metabolically regulated in vivo, in response to changes in the growth conditions [Wieslander et al. (1980) Biochemistry 19, 3650; Lindblom et al. (1986) Biochemistry 25, 7502]. To investigate the mechanism behind the lipid regulation, we have here studied bilayers of mixtures of unsaturated MGlcDG and DGlcDG, containing a small fraction of biosynthetically incorporated perdeuterated palmitic acid, with 2H NMR. The order-parameter profile of the acyl chains and an apparent transverse spin relaxation rate (R2) were determined from dePaked quadrupole-echo spectra. The order of the acyl chains in DGlcDG-d31 increases upon addition of protonated MGlcDG, whereas the order of MGlcDG-d31 decreases when DGlcDG is added. The variation of order with lipid composition is rationalized from simple packing constraints. R2 increases linearly with the square of the order parameter (S2) up to S approximately 0.14; then, R2 goes through a maximum and decreases. The increase in R2 with S2, as well as the magnitude of R2, is largest for pure MGlcDG-d31, smallest for DGlcDG-d31, and similar for mixtures with the same molar ratio of MGlcDG/DGlcDG but with the deuterium label on different lipids.(ABSTRACT TRUNCATED AT 250 WORDS)

Membrane Lipid Composition and Cell Size of Acholeplasma laidlawii Strain A are Strongly Influenced by Lipid Acyl Chain Length

“…For example, large fractions of acylGlc-acy1,Gro and acy1,Gro (210% of each) were found together with fairly low fractions of Glc-acy1,Gro ( c 2 5 % ) at a low degree of chain unsaturation (Figs 3 -5). The phase equilibria for native Glc-acy1,Gro species containing such acyl chains are shifted towards lamellar phases (Lindblom et al, , 1993Eriksson et al, 1991). The complementary property of the three lipids is also seen in a plot of the total fraction of these lipids (Fig.…”

“…7). Most likely, the Glc-acy1,Gro synthesized by A. laidlawii under these conditions forms L, phases close to, or above, the growth temperature (Eriksson et al, 1991). The substantial amounts of the nonbilayer-promoting lipids acy1,Gro and acylGlc-acy1,Gro synthesized, especially with mainly saturated chains (Figs 4 and 5), are probably essential complements to Glc-acy1,Gro.…”

“…Glc-acy1,Gro is the major lipid in A. laidlawii membranes, which is able to form reversed nonlamellar phases like cubic and HI, phases. However, lamellar phases can be formed under physiological conditions with both synthetic (Mannock et al, 1990) and native (Eriksson et al, 1991) Glc-acy1,Gro species with short, saturated acyl chains. Saturated chains with c,, values of 16-18, and low growth temperatures, stimulate the synthesis of Glc-acy1,Gro (reviewed in Rilfors et al, 1993).…”

“…contain 47,61,46, and 97 moU100 mol 18: l c chains, respectively, and species 5 contains 92 moUlOO mol elaidoyl (18: l t ) chains. The data are compiled fromMannock et al (1990),Wieslander et al (1978),Lindblom et al (1986Lindblom et al ( , 1993 andEriksson et al (1991).…”

Lateral organization in Acholeplasma laidlawii lipid bilayer models containing endogenous pyrene probes

“…The location of pyrene has nevertheless been determined to be located close to the bilayer center. MGlcDAG, shown to increase order [54], is organized laterally in this five‐lipid model system in a way that gives no significant contribution to the ordering of the membrane bilayer, according to the experimental design model.…”