Refined structure of the lipophosphoglycan of Leishmania-donovani

The primary structure of the major surface glycoconjugate of Leishmania donovani parasites, a lipophosphoglycan, has been further characterized. The repeating PO₄-6Galpß1-4Man disaccharide units, which are a salient feature of the molecule, are shown to terminate with one of several neutral structures, the most abundant of which is the branched trisaccharide Galpß1-4(Manpa1-2)Man. The phosphosaccharide core of lipophosphoglycan, which links the disaccharide repeats to a lipid anchor, contains 2 phosphate residues. One of the core phosphates has previously been localized on O-6 of the galactosyl residue distal to the lipid anchor; the second phosphate is now shown to be on O-6 of the mannosyl residue distal to the anchor and to bear an a-linked glucopyranosyl residue. Also, the anomeric configuration of the unusual 3-substituted Galf residue in the phosphosaccharide core is established as ß. The complete structure of the core is thus PO₄-6Galpa1-6Galpa1-3Galfß1-3[Glcpa1-PO₄-6]Manpa1-3Manpa1-4GlcNa1-. This further clarification of the structure of lipophosphoglycan may prove beneficial in determining the structure-function relationships of this highly unusual glycoconjugate.