Branched Monosialo Gangliosides of the Lacto-Series Isolated from Bovine Erythrocytes: Characterization of a Novel Ganglioside, NeuGc-Isooctaosylceramide

We report the isolation, purification, and structural characterization of three monosialo gangliosides (G-1., G-2, and G-3) from bovine erythrocytes. Each of the purified compounds migrates as a single band on thin-layer chromatography in three solvent systems. All three gangliosides contain ceramide (Cer) as the lipid portion, with d18:1 sphingosine as the predominant long-chain base and with C18:0, C18:1, C20:0, C20:1, and C22:I fatty acids, as determined by gas chromatography. The structural characterization of the carbohydrate moieties of G-1, G-2, and G-3 involved glycosyl composition analysis, methylation studies, sequential exoglycosidase hydrolysis, and one-dimensional 1H NMR spectroscopy of the native gangliosides. Furthermore, the oligosaccharides were released from the sphingolipids by endoglycoceramidase and fully sequenced by one- and two-dimensional 1H NMR spectroscopy in conjunction with fast-atom-bombardment mass spectrometry and exoglycosidase treatment. The structures are as follows: [formula] Gangliosides such as G-1, G-2, and G-3, with branched oligosaccharide chains comprising a number of N-acetyllactosamine (Gal-GlcNAc) moieties, are abundant in erythrocytes from various mammalian species. The simultaneous occurrence of sialic acid and α-galactose as terminal sugars in these gangliosides, however, is relatively rare. Specifically, G-1 represents a ganglioside with a novel structure.