The hydrophobic mannoside Manα1-6Manα1-S-(CH₂)₇-CH₃ acts as an acceptor for the UDP-Gal:glycosylphosphatidylinositol anchor α1,3-galactosyltransferase of Trypanosoma brucei

The variant surface glycoproteins (VSGs) of Trypanosoma brucei are attached to the plasma membrane via a glycosylphosphatidylinositol (GPI) membrane anchor, This anchor contains the core sequence ethanolamine-PO₄-6Manα1-2Manα1-6Manα1-4GlcNα1-6myo- inositol, which is conserved in all GPI anchors, and a unique αGal side chain attached to the 3-position of the αMan residue adjacent to the αGlcN residue. Here we report that trypanosome membranes can catalyse the transfer of Gal from UDP-Gal to the hydrophobic thioglycoside Manα1-6Manα1-S-(CH₂)₇-CH₂. Characterization of the galactosylated products by electrospray mass spectrometry, exoglycosidase digestion and periodate-oxidation studies revealed that the major product was Manα1-6(Galα1-3)Manα1-S-(CH₂)₇-CH₂. The similarity of this product to part of the mature VSG GPI anchor suggests that the thioglycoside is able to act as an acceptor for the trypanosome-specific UDP-Gal-GPI anchor α1,3-galactosyltransferase.