Structural mapping of the glycans from the egg glycoproteins of Schistosoma mansoni and Schistosoma japonicum: identification of novel core structures and terminal sequences

The structural diversity of the glycans from Schistosoma mansoni and Schistosoma japonicum egg glycoproteins was investigated using high sensitivity fast atom bombardment mass spectrometric screening of glycan pools released enzymically or chemically from egg extracts. The egg glycoproteins from the two species carry a comparable range of high mannose and complex type N-glycans with both lacNAc and lacdiNAc constituting the backbones of the antennae in the latter class. Truncated N-glycans similar to those found on nematodes, insects, and plants were also identified. Sequential digestion with peptide N-glycosidase F and peptide N-glycosidase A afforded effective release and separation of N-glycans with nonfucosylated or α6-monofucosylated trimannosyl N,N'-diacetyl-chitobiose cores from those carrying core α3-, α6-difucosylation, all of which were found to be present in both species. Remarkably, a portion of the N-glycans from S.mansoni eggs was shown to be based on a xylosylated, α6-fucosylated trimannosyl core, whereas a portion of those from S.japonicum contains a xylosylated α3-, α6-difucosylated core which has not been previously described in any organism. O-Glycans were chemically released from the de-N-glycosylated glycopeptides and found to carry terminal sequences similar to those in the N-glycans. This study provides further evidence that multi-fucosylated terminal HexNAc units, previously identified on the cercarial glycocalyx O-glycans and egg glycosphingolipids, and now on the egg N- and O-glycans, are unique features of S.mansoni glycans. These multifucosylated terminal structures, which were not detected on the egg glycans of S.japonicum, are likely to constitute the cross-reacting epitopes between the eggs and cercariae of S.mansoni. Interestingly other HexNAc termini, including an unusual stretch of HexNAc3, were found to be common to both species. The mapping studies reported in this article provide an important foundation for further structural work in this challenging and important area of glycobiology.