The carbohydrate structures of Trypanosoma brucei brucei MITat 1.6 variant surface glycoprotein. A re-investigation of the C-terminal glycan.

We have studied the oligosaccharide chains of the variant surface glycoprotein (VSG) of Trypanosoma brucei brucei MITat 1.6. Glycopeptides were generated by Pronase digestion, purified by gel permeation and ion-exchange chromatography, and structurally characterized by 1H and 31P NMR spectroscopy in combination with chemical composition analyses. The two glycopeptide fractions obtained each proved to be homogeneous in their peptide and heterogeneous in their carbohydrate structures. The fraction representing the "internal" N-glycosylation site of the VSG was found to contain high-mannose type oligosaccharides with structures Man7-9GlcNAc2 linked to Asn-Ala-Thr. The other glycopeptide fraction contained the membrane-anchoring C-terminal glycan of the VSG attached to Asp. Its oligosaccharide structures are of the glycosylphosphatidylinositol (GPI) type: [structure: see text] This structure includes revisions of multiple structural features published for the GPI anchor of T. b. brucei MITat 1.6 VSG by Schmitz et al. (1987) Biochem. Biophys. Res. Commun. 146: 1055-1063.