Conformation of the oligosaccharide chain of G(M1) ganglioside in a carbohydrate-enriched surface.

The solution structure of ganglioside G(M1) carbohydrate moiety at the surface of a 102-kDa lipid-modified-G(M1) micelle is investigated by high-resolution 1H-NMR in H2O. The micellar surface can be considered a cluster-like lateral distribution of the gangliosides, each single monomer being anchored in a carbohydrate-enriched model membrane matrix. 1H NOESY measurements at short mixing times reveal a rigid trisaccharide core -beta-GalNAc-(1-4)-[alpha-Neu5Ac-(2-3)]-beta-Gal- and a more flexible beta-Gal-(1-3)-beta-GalNAc- terminal glycosidic bond. In the lipid-modified G(M1) ganglioside micellar system, there is no evidence that intermolecular side-by-side carbohydrate interactions modulate, or alter in any way, the head-group spatial arrangement. Possible intermonomer interactions at the level of the branched trisaccharide portion were further investigated on mixed micelles of natural N-glycolyl- and N-acetylneuraminic acid containing G(M1) in D2O, taking advantage of the different NMR features of N-glycolyl- and N-acetylneuraminic acids, which allow discrimination between sialic acid ring proton signals. Measurements of the water/ganglioside-OH proton chemical exchange rates suggest hydroxyl group involvement at position 8 of sialic acid in strong intramolecular interaction processes.