Selective expression of different fucosylated epitopes on two distinct sets of Schistosoma mansoni cercarial O-glycans:: identification of a novel core type and Lewis X structure

The glycobiology of Schistosoma mansoni is dominated by developmentally regulated expression of various fucosylated structures, most notably the Lewis X epitope and a multifucosylated sequence, Fuc alpha1 --> 2Fuc alpha1 -->, in its various forms. For the infective cercarial stage, Lewis X has been structurally identified on glycosphingolipids and N-glycans of total glycoprotein extracts, and a population of multifucosylated glycoproteins were found to carry a unique terminal sequence, +/- Fuc alpha1 --> 2Fuc alpha1 --> [3GalNAc beta1 -->4(Fuc alpha1 --> 2Fuc alpha1 --> 2Fuc alpha1 -->3)GlcNAc beta1 --> 3Gal alpha1 -->](n), on their O-glycans, Using a mass spectrometry approach coupled with chromatographic separation, sequential exoglycosidase digestion, periodate oxidation, and other chemical derivatization, we demonstrate that Lewis X could also be carried on the cercarial O-glycans, but the two distinctive sets of fucosylated epitopes were conjugated to two different core structures. Lewis X, lacNAc, or single GlcNAc was found to attach directly to the --> 3Gal beta1 --> 3GalNAc core and indirectly via another -beta Gal residue branching off from C6 of the reducing end GalNAc to give a biantennary-like structure. The -->3(+/- Gal beta1 -->6)Gal beta1 -->3(--> 3Gal beta1 -->6)GalNAc care thus characterized represents a novel core type for O-glycans, In contrast, the previously characterized multifucosylated terminal sequences were carried on conventional type 1 and 2 cores. The smallest structures of the reductively released O-glycans were defined as GalNAc beta1 --> 4GlcNAc beta1 --> 3Gal beta1 --> 3GalNAcitol with a total of two to four fucoses attached to the terminal lacdiNAc, alpha -Galactosylation of the nonreducing terminal beta -GalNAc instead of fucose capping leads to further elongation with another lacdiNAc unit that could also extend directly from C6 of the reducing end GalNAc and similarly elongated or terminated.