Determination of conformational properties of glycolipid head groups by deuterium NMR of oriented multibilayers

Abstract

The conformations and orientations of the glucose and glycerol moieties of a monoglucosyl lipid in hydrated bilayers have been determined in detail by deuterium nuclear magnetic resonance (2H NMR). Multibilayer membranes of 1,2-di-O-tetradecyl-3-O-(beta-D-glucopyranosyl)glycerol (DTGL), of dimyristoylphosphatidylcholine (DMPC), and of a mixture of DTGL and DMPC were oriented between glass plates. The glucolipid was selectively labeled with deuterium on the pyranose ring and at C3 of glycerol, whereas DMPC was labeled at the C4 position of the sn-2 chain. Quadrupolar splittings were measured as a function of the angle between the bilayer normal and the magnetic field direction. The results establish that the director of motional averaging, the direction about which motion and order are axially symmetric, is the bilayer normal for all the head group, the glycerol backbone, and the hydrophobic core. Segmental order parameters were determined to be 0.45, 0.65, and 0.40, respectively, for the various regions of DTGL in the membranes. The latter results indicate that there is some motion on the time scale of 10(5) s-1 about the C1'(glucose)-O-C3(glycerol) glycosidic bond but that its amplitude is very restricted. Comparison of 1H-decoupled and 1H-coupled 2H NMR spectra of the C3-labeled glycolipid gave estimates of the 2H-2H dipolar coupling between the deuterons at this position. The orientation of the glycerol C3 hydroxymethylene subunit was calculated relative to the bilayer normal, and the C2-C3 bond was found to be tilted away from the bilayer normal by 3 +/- 1 degree.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of plant sterols on water permeability and on acyl chain ordering of soybean phosphatidylcholine bilayers.

“…The accuracy of the angular settings was determined by multiple settings, especially at 900 and was found to be +20. We checked by changing the plate orientation that the axis of rotation of DMPC-d27 was the normal to the bilayer (18). Quadrupolar splittings (AvQ) for all the positions along the sn-2 acyl chain of dimyristoylphosphatidylcholine can be measured directly from the NMR spectra recorded at 900 (Fig.…”

Orientation of the saccharide chains of glycolipids at the membrane surface: Conformational analysis of the glucose-ceramide and the glucose-glyceride linkages using molecular mechanics (MM3)

“…In order to account for different rotamers of the glucose 6-hydroxymethyl group both the gg and the gt conformers [for definition see Jeffrey (1990)l of GlcCer(n) and GlcCer-(h) were tested. These calculations gave very similar results for theggand gt conformers.…”

Quantitation of the phase preferences of the major lipids of the Acholeplasma laidlawii B membrane

“…We therefore suggest that the stronger lamellar phase preference of PG compared to DGDG, and particularly to MGDG, can be explained by its greater degree of hydration (Wieslander et a/., 1978(Wieslander et a/., , 1981Lindblom et a/., 1986;Eriksson et al, 1991), by its charged character , and by its greater degree of conformational freedom at the bilayer surface (Jarrell et al, 1986(Jarrell et al, , 1987aRenou et a/., 1989;Carrier et a/., 1989). Moreover, the PG headgroup is aligned with its long axis nearly parallel to the bilayer surface whereas the sugar headgroups of MGDG and DGDG extend further away from the bilayer surface (Jarrell et al, 1986(Jarrell et al, , 1987aRenou et al, 1989;Carrier et a/., 1989). As well, the strength of polar headgroup interactions at the polar surface of PG is clearly less than that of MGDG or DGDG as shown by the much lower gel to liquid-crystalline phase temperature of the former when the fatty acid composition of these two lipids are identical (Silvius & McElhaney, 1978a,b;Silvius et al, 1980).…”