The parasitic nematode Oesophagostomum dentatum synthesizes unusual glycosaminoglycan-like O-glycans

摘要

O-glycosylation is probably one of the most varied sets of post-translational modifications across all organisms, but amongst the most refractory to analyse. In animals, O-xylosylation of serine residues represents the first stage in the synthesis of glycosaminoglycans, whose repeat regions are generally analysed as fragments resulting from enzymatic or chemical degradation, whereas their core regions can be isolated by β-elimination or endo-β-xylosidase digestion. In the present study, we show that hydrazinolysis can be employed for release of glycosaminoglycan-type oligosaccharides from nematodes prior to fluorescent labelling with 2-aminopyridine. While various [HexNAcHexA]nGal2Xyl oligosaccharides were isolated from the model organism Caenorhabditis elegans, more unusual glycosaminoglycan-type glycans were found to be present in the porcine parasite Oesophagostomum dentatum. In this case, as judged by MS/MS before and after hydrofluoric acid or β-galactosidase digestion, core sequences with extra galactose and phosphorylcholine residues were detected as [(±PC)HexNAcHexA]n(±PC)Galβ3-(±Galβ4)Galβ4Xyl. Thus, hydrazinolysis and fluorescent labelling can be combined to analyse unique forms of O-xylosylation, including new examples of zwitterionic glycan modifications.