BIOSYNTHESIS OF LEISHMANIA LIPOPHOSPHOGLYCAN - SOLUBILIZATION AND PARTIAL CHARACTERIZATION OF THE INITIATING MANNOSYLPHOSPHORYLTRANSFERASE

Lipophosphoglycan (LPG) is the predominant surface glycoconjugate of L eishmania promastigotes and consists of a capped polymer of Gal(beta 1 ,4)Man(alpha 1)-PO4 repeating units attached through a glycan core to a phosphatidylinositol anchor, We have solubilized the mannosylphospho ryltransferase from L.donovani promastigotes that initiates repeating unit synthesis using beta-dodecylmaltoside and other nonionic detergen ts with long alkyl chains. The detergentsolubilized enzyme, in the pre sence of GDP-Man and Mn2+ transferred Man(alpha 1)-PO4 to two exogenou s acceptor substrates: the glycan core from LPG and stachyose, a tetra saccharide terminating in the same Gal(alpha 1,6)Gal(alpha) disacchari de as glycan core, The activity is saturable with respect to GDP-Man, but not with respect to stachyose, suggesting that more than Gal(alpha 1,6)Gal(alpha) is required in the acceptor substrate for optimal acti vity, In contrast to promastigotes, Leishmania amastigotes express low er levels of LPG by downregulating the addition of the repeating units , We compared the relative activity of the initiating mannosylphosphor yltransferase in microsomal fractions from axenic amastigotes and its promastigote counterpart, using stachyose as the acceptor substrate, T he promastigote membranes mere 3-fold more active relative to the amas tigote membranes, These results provide evidence that the initiating m annosylphosphoryltransferase is developmentally regulated during the l ife-cycle of the Leishmania parasite.