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Oligosaccharide order in a membrane-incorporated complex glycosphingolipid
H Jarrell1, D Singh, C W Grant
1Department of Biochemistry, University of Western Ontario, London, Canada.
Biochimica Et Biophysica Acta
|January 31, 1992
Summary
Deuterated galactosylceramide (GalCer) and ganglioside GM1, when incorporated into lipid bilayers, exhibit restricted headgroup motion. This demonstrates that complex glycolipids can possess orientational order within fluid membranes.
Area of Science:
- Biophysics
- Membrane Biology
- Glycosphingolipid Chemistry
Background:
- Galactosylceramide (GalCer) and ganglioside GM1 are key glycosphingolipids in cell membranes.
- Understanding their orientation and dynamics within lipid bilayers is crucial for cell function.
- Previous studies suggested limited headgroup mobility, but direct evidence in fluid membranes was lacking.
Purpose of the Study:
- To investigate the orientational order of GalCer and GM1 headgroups within fluid 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) lipid bilayers.
- To determine if complex gangliosides exhibit restricted motion similar to simpler glycolipids.
- To provide direct evidence for headgroup ordering in complex glycolipids within fluid membranes.
Main Methods:
- Deuterium (2H) labeling of the terminal galactosyl residues of GalCer and GM1.
- Incorporation of labeled lipids into POPC multibilayers at biologically relevant concentrations.
- Analysis of lipid dynamics and ordering using 2H-Nuclear Magnetic Resonance (NMR) spectroscopy.
Main Results:
- 2H-NMR spectra revealed restricted headgroup motion and effective axial symmetry for GalCer in POPC bilayers.
- GM1, labeled in its terminal galactose residue, showed 2H-NMR spectra similar to GalCer.
- This indicates significant restriction of motion around glycosidic and sugar-ceramide bonds in the GM1 headgroup.
Conclusions:
- The study provides the first direct demonstration of headgroup orientational order for a complex glycolipid (GM1) in fluid bilayer membranes.
- Both GalCer and GM1 exhibit comparable degrees of orientational averaging about the bilayer normal.
- This headgroup ordering suggests a mechanism for modulating membrane receptor properties via surface effects on average headgroup orientation and conformation.