Characteristic structural features of schistosome cercarial N-glycans: expression of Lewis X and core xylosylation

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Abstract
Schistosomal egg N-glycans are the only examples in nature that have been structurally shown to contain β2-xylosylation, α6-fucosylation, and α3-fucosylation on the N,N′-diacetyl chitobiose core. We present evidence that core difucosylated and xylosylated N-glycans are characteristics of Schistosoma japonicum eggs but not of the cercariae and adults, for which neither core xylosylation nor α3-fucosylation could be readily detected. In contrast, a majority of the N-glycans from Schistosoma mansoni cercariae but not the adults are core xylosylated. Tandem mass spectrometry analysis coupled with chromatographic mapping, sequential exoglycosidase digestion, and methylation analysis were employed to unambiguously define the structures of core β2-xylosylated, α6-fucosylated N-glycans from S. mansoni cercariae. Unexpectedly, a majority of these N-glycans were found to carry Lewis X determinant, Galβ1→4(Fucα1→3)GlcNAcβ1→, on the nonreducing termini of mono- and biantennary structures. The Lewis X–containing glycoproteins were found to be distinct from those carrying the complex, multifucosylated glycocalyx O-glycans reported previously. The corresponding N-glycans from S. japonicum cercariae are likewise dominated by Lewis X termini but without the core xylosylation. We concluded that the invading cercariae present an important and abundant source of Lewis X antigens, which may contribute to the induced humoral response upon infection. Following transformation and development into the adults, the N-glycans synthesized comprise a significantly larger amount of high mannose and fucosylated pauci-mannose structures in comparison with the cercarial N-glycans. A portion of the mono- and biantennary complex types were identified to carry Lewis X and fucosylated LacdiNAc termini, which could also be detected by mass spectrometry analysis on larger, complex-type structures.

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