CHARACTERIZATION OF LIPOPHOSPHOGLYCAN FROM A RICIN-RESISTANT MUTANT OF LEISHMANIA-MAJOR

One of the virulence factors of the protozoan parasite Leishmania majo r is the surface glycoconjugate, lipophosphoglycan (LPG), A Ricin-resi stant mutant of L. major was generated and characterised,vith respect to its virulence in mice and the structure and expression of LPG, The LPG from this mutant (1F6-B5) retained the tripartite structure of wil d-type LPG, comprising a glycosylphosphatidylinositol (GPI) anchor lin ked to a phosphorylated disaccharide backbone terminating in a nonredu cing neutral oligosaccharide cap, The structure of the GPI anchor and the major capping oligosaccharide were identical to wild-type LPG, How ever, there were variations in the number of phosphorylated repeats (P O4-6Gal(beta 1-4)Man(alpha 1-) comprising the backbone of LPG, althoug h the degree of substitution with side branches (approx, 95%) was simi lar to that of wild-type LPG, Thus, the mutant LPG was shorter in leng th having, on average, 15 repeat units per molecule compared with 30 i n the wild-type LPG, The mutant LPG contained both arabinose (Ara(beta 1-2)[Gal(beta 1-3)-](1,2)) and galactose ([Gal(beta 1-3)-](1-8)) capp ed side branches linked to the backbone, In contrast to wild-type LPG, the number of arabinose-capped side chains was significantly reduced, and a new population of galactose-capped (Gal(beta 1-3)](5-8)) side b ranches was present, The level of LPG expression in mutant parasites w as approximately one-tenth of the wildtype parasite, The mutant parasi tes were avirulent in mice, Over a period of 18 months, they did not c ause lesions and organisms could not be isolated from the draining lym ph nodes.