Association of gangliosides with the lymphocyte plasma membrane studied using radiolabels and spin labels.
Gangliosides are known to act as potent suppressors of lectin-stimulated lymphocyte activation when added to the culture medium. Since this effect may be mediated via ganglioside association with (or insertion into) the plasma membrane, we have used 3H- and spin-labelled derivatives of mixed gangliosides to probe the nature of this interaction. Gangliosides bind rapidly to the lymphocyte membrane and show no preference for association with either inside-out or right-side-out membrane vesicles. Around 20% of the bound gangliosides can be removed by repetitive washing, and a further 22-28% by treatment with pronase for 1 h, suggesting that this fraction is tightly bound to membrane proteins at the cell surface. The ESR spectrum of membrane-bound gangliosides did not resemble the spin-exchanged spectrum of micellar spin-labelled gangliosides in aqueous solution, but was similar to that seen for 5 mol% ganglioside spin label in liposomes of egg phosphatidylcholine. This suggests that the bulk of the membrane-bound gangliosides are inserted and molecular dispersed in the lymphocyte membrane. Binding of wheat-germ agglutinin to lymphocyte-associated gangliosides results in specific immobilization of the carbohydrate headgroup, while concanavalin A and other lectins have little or no effect on oligosaccharide mobility. Membrane-inserted gangliosides show a response to lectin binding which is qualitatively different from that seen for gangliosides in bilayers of phosphatidylcholine.
D000818:Animals; D002417:Cattle; D002462:Cell Membrane / Q000032:analysis; D004578:Electron Spin Resonance Spectroscopy; D005732:Gangliosides / Q000032:analysis*; D037102:Lectins / Q000494:pharmacology; D008214:Lymphocytes / Q000166:cytology*; D008433:Mathematics; D008823:Micelles; D013113:Spin Labels / Q000378:metabolism*; D013552:Swine
D005732:Gangliosides; D037102:Lectins; D008823:Micelles; D013113:Spin Labels