Characterization of the glucosyltransferases that assemble the side chainsof the Indian Leishmania donovani lipophosphoglycan

The life cycle of Leishmania parasites within its sand fly vector involves the development of extracellular promastigotes from a noninfective, "procyc lic" stage into an infective, "metacyclic" stage that is adapted for transm ission in the fly and survival in the mammalian host. Lipophosphoglycan (LP G), the predominant surface glycoconjugate in both procyclic and metacyclic stages, is a critical virulence determinant. LPG is a multidomain molecule ; the structural polymorphisms among species lie in branching from the back bone 6Gal beta 1,4Man(alpha 1)-PO4 repeat units and in the composition of t he small oligosaccharide caps. We have recently demonstrated that the LPG f rom an Indian isolate of Leishmania donovani differs from a Sudanese strain by possessing one or two side chain beta(1,3)-linked glucose residues. We now have characterized the glucosyltransferase activities responsible for g lucosylating the LPG. When incubated with UDP-[H-3]glucose and Mn2+, micros omal membranes from the Indian isolate transferred [SH]glucose to the repea t units of the exogenous acceptor Sudanese L. donor,ani LPG, which does not contain any side chain branching. Glucose addition was maximal at 28 degre es C, the optimal growth temperature of procyclic L. donovani. Consistent w ith the lack of side chain branching in its LPG, Sudanese L. donovani showe d minimal glucosyltransferase activity. Indian metacyclic promastigotes, in contrast to procyclic promastigotes, express no glucose side chains off th e repeat units. Therefore, we compared the relative activity of the glucosy ltransferases in microsomes from procyclic and metacyclic promastigotes and observed approximately 80% less activity in the latter. These results prov ide evidence that the glucose side chain addition to LPG is developmentally regulated during the parasite's life cycle and that the glucosyltransferas es of L. donovani are Strain specific. (C) 1999 Academic Press.