Expression of a stage-specific lipophosphoglycan in Leishmania major amastigotes

Abstract

Amastigotes of Leishmania major were isolated from infected mice and radiolabeled for 2 h with [ 3H]galactose. An acidic [ 3H]glycoconjugate was extracted from a dilipidated residue fraction with the solvent water/ethanol/diethylether/pyridine/NH 4OH (15:15:5:1:0.017). The radioactively labeled glycoconjugate was found to possess the following characteristics that were similar to the lipophosphoglycan extractable from promastigotes: (i) migrated as a broad band upon electrophoresis on SDS polyacrylamide gels; (ii) deaminated with nitrous acid; and (iii) hydrolyzed with phosphatidylinositol-specific phospholipase C. Furthermore, analysis of the aqueous soluble material released by the latter enzyme revealed a negatively-charged [ 3H]polysaccharide intermediate in size compared to the analogous portions of LPG isolated from non-infective and metacyclic promastigotes. Most importantly, the [ 3H]polysaccharide was found to contain phosphate and was susceptible to mild acid hydrolysis, establishing that the intact molecule is a lipophosphoglycan. A structural difference, however, was found in the major, mild acid-generated fragment of the amastigote phosphoglycan, which was larger in size and not as anionic as the analogous fragment from the promastigote phosphoglycans. These results indicate that the amastigotes do express a lipophosphoglycan, but that it is structurally distinct from its promastigote counterparts.