STRUCTURE OF LEISHMANIA-MEXICANA LIPOPHOSPHOGLYCAN

Lipophosphoglycan (LPG) was isolated from the culture supernatant of L eishmania mexicana promastigotes and its structure elucidated by a com bination of H-1 NMR, fast atom bombardment mass spectrometry, methylat ion analysis, and chemical and enzymatic modifications. It consists of the repeating phosphorylated oligosaccharides PO4-6Gal-beta-1-4Man-al pha-1- and PO4-6[Glc-beta-1-3]Gal-beta-1-4Man-alpha-1-, which are link ed together in linear chains by phosphodiester linkages. Each chain of repeat units is linked to a phosphosaccharide core with the structure pha-1-PO4-6]Man-alpha-1-3Man-alpha-1-4GlcNH2-alpha 1-6 myo-inositol, where the myo-inositol residue forms the head group of a lyso-alkylpho sphatidylinositol moiety. The nonreducing terminus of the repeat chain s appear to be capped with the neutral oligosaccharides Man-alpha-1-2M an, Man-alpha-1-2Man-alpha-1-2Man, or Man-alpha-1-2[Gal-beta-1-4]Man. Cellular LPG, isolated from promastigotes, has a very similar structur e to the culture supernatant LPG. However, it differs from culture sup ernatant LPG in the average number of phosphorylated oligosaccharide r epeat units (20 versus 28) and in alkyl chain composition. Although cu lture supernatant LPG contained predominantly C24:0 alkyl chains, cell ular LPG contained approximately equal amounts of C24:0 and C26:0 alky l chains. It is suggested that culture supernatant LPG is passively sh ed from promastigotes and that it may contribute significantly, but no t exclusively, to the "excreted factor" used for serotyping Leishmania spp. Comparison of L. mexicana LPG with the LPGs of Leishmania major and Leishmania donovani indicate that these molecules are highly conse rved but that species-specific differences occur in the phosphorylated oligosaccharide repeat branches and in the relative abundance of the neutral cap structures.