Glycosphingolipids: deuterium NMR study of the influence of ceramide fatty acid characteristics on the carbohydrate headgroup in phospholipid bilayers

Abstract

Galactosylceramides bearing a variety of different pure fatty acid chains were 2H labeled in the carbohydrate headgroup at C6 of the terminal galactose residue, for study by 2H NMR. Fatty acids investigated included the 24-carbon saturated lignoceric acid, 18-carbon saturated stearic acid, cis-9,10-unsaturated oleic acid, and D- and L-stereoisomers of alpha-hydroxystearic acid. Headgroup-deuterated glycolipids were incorporated at 10 mol % into unsonicated bilayers of 1-palmitoyl-2-oleoylphosphatidylcholine, and 2H NMR spectra were recorded at 65 and 40 degrees C. Under these experimental conditions, the membranes studied were primarily in the liquid-crystalline phase. At a given temperature, spectra for deuterated galactosylceramides dispersed in the fluid phase were remarkably similar, regardless of the nature of the fatty acid attached to the glycolipid sphingosine backbone. In each case, the spectrum consisted of a superposition of two quadrupolar powder patterns of approximately equal intensity. The spectra may be interpreted as arising from equal populations of two stereoisomers (pro-R and pro-S) of the deuterated galactose hydroxymethyl function, which is undergoing rapid (greater than 10(6) s-1) interconversion among the possible rotamers about the C5-C6 bond of the sugar ring. Within experimental error, the only fatty-acid-induced spectral difference detected among these glycosphingolipids deuterated in the carbohydrate headgroup was in the species with alpha-hydroxy-substituted fatty acids. At 65 degrees C, N-(D-alpha-hydroxy)stearoyl- and N-(L-alpha-hydroxy)stearoylgalactosylceramide gave rise to the same quadrupole splittings, but these differed marginally from the splittings observed for the other glycolipids studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Transbilayer diffusion of divalent cations into liposomes mediated by lipidic particles of phosphatidate

“…6A,B), similar to that described for bilayers in the fluid state (Singh et al 1992). Liposomes incubated in the presence of 10 mM of Mg 2÷ did not modify the size and the structure of their lipid bilayers (Fig.…”

“…Then, liposomes were cooled down at 4°C during I h before freeze-fracture. An aliquot of these liposomes was sandwiched between a pair of Balzers (Nashua, NH) copper support plates and frozen in Freon 22 cooled in liquid nitrogen (Singh et al 1992). Glycerol at final concentration of 15% was added to prevent freeze damage of the lipid samples (Verkleij et al 1982;Gaillard et al 1991).…”

Absence of 2-Hydroxylated Sphingolipids Is Compatible with Normal Neural Development But Causes Late-Onset Axon and Myelin Sheath Degeneration

“…This hypothesis is supported by the observation that HFAGalC and HFA-sulfatide form more stable calcium-dependent complexes than their nonhydroxylated counterparts (Menikh et al, 1997;Koshy et al, 1999). Biophysical studies on lipid monolayers showed that the phase behavior of ceramides is significantly affected by 2-hydoxylation (Singh et al, 1992). The galectin-4-dependent stabilization of so-called "super rafts," detergent-resistant membranes that are detergent insoluble at 37°C (Braccia et al, 2003), appears to depend on the specific binding of galectin-4 to the 2-hydroxylated isoforms of GalC and sulfatide (Delacour et al, 2005).…”

Exposure to galactose oxidase of GM1 ganglioside molecular species embedded into phospholipid vesicles

“…These possibilities seem to be ruled out by previous data [29,30] indicating that the lipid chain length does not significantly affect the conformation of saccharide moiety. Moreover, it has been reported that in the case of galactosylceramide embedded in PC vesicles [lo], GAO preferentially affects the molecular species carrying longer lipid chains, their saccharide moiety being more exposed above the apolar-polar interface of the bilayer.…”