Abstract
Previous studies have shown that the glycoprotein oligosaccharides synthesized by adult Schistosoma mansoni, the organism responsible for human schistosomiasis, are unusual in that they contain terminal beta-GalNAc residues and lack sialic acid. These observations and other studies indicating that schistosome glycoproteins and glycolipids are antigenic in infected animals led us to investigate the structures of the glycosphingolipids synthesized by these organisms and to determine whether they are structurally related to those synthesized by their vertebrate hosts. For our studies, adult schistosomes were metabolically radiolabeled with either [3H]galactose or [3H]glucosamine, and the newly synthesized glycosphingolipids were isolated and characterized. The major glycosphingolipids synthesized by adult schistosomes were found to be galactosylceramide and glucosylceramide. The adult worms synthesized no lactosylceramide (Gal beta 1-4Glc-ceramide), a common constituent of vertebrate cells; however, another disaccharide-containing glycosphingolipid cleavable by ceramide glycanase was found. The results of compositional and methylation analyses and exoglycosidase treatments demonstrated that this ceramide-disaccharide has the structure GalNAc beta 1-4Glc-ceramide. We also found that extracts of adult schistosomes are unable to transfer Gal from UDP-Gal to glucosylceramide, whereas extracts of Chinese hamster ovary cells, as a control, are able to do so, confirming that schistosomes are unable to synthesize lactosylceramide. Low levels of higher molecular weight glycosphingolipids were also found to be synthesized by adult schistosomes, and although their levels were too small to allow definitive characterization, compositional analyses indicated that they also contained GalNAc. We have tentatively designated the new disaccharide structure GalNAc beta 1, 4Glc- the "schistocore", which may represent a new type of glycosphingolipid core series.
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