Galactose-containing glycosylphosphatidylinositols in Trypanosoma brucei.
Chromatography, Ion Exchange
Chromatography, Thin Layer
Phosphoric Diester Hydrolases
Trypanosoma brucei brucei
Variant Surface Glycoproteins, Trypanosoma
Many eukaryotic surface glycoproteins, including the variant surface glycoproteins (VSGs) of Trypanosoma brucei, are synthesized with a carboxyl-terminal hydrophobic peptide extension that is cleaved and replaced by a complex glycosylphosphatidylinositol (GPI) membrane anchor within 1-5 min of the completion of polypeptide synthesis. We have reported the purification and partial characterization of candidate precursor glycolipids (P2 and P3) from T. brucei. P2 and P3 contain ethanolamine-phosphate-Man alpha 1-2Man alpha 1-6Man alpha 1-GlcN linked glycosidically to an inositol residue, as do all the GPI anchors that have been structurally characterized. The anchors on mature VSGs contain a heterogenously branched galactose structure attached alpha 1-3 to the mannose residue adjacent to the glucosamine. We report the identification of free GPIs that appear to be similarly galactosylated. These glycolipids contain diacylglycerol and alpha-galactosidase-sensitive glycan structures which are indistinguishable from the glycans derived from galactosylated VSG GPI anchors. We discuss the relevance of these galactosylated GPIs to the biosynthesis of VSG GPI anchors.