ISOLATION OF VIRULENCE GENES DIRECTING SURFACE GLYCOSYL-PHOSPHATIDYLINOSITOL SYNTHESIS BY FUNCTIONAL COMPLEMENTATION OF LEISHMANIA

Trypanosomatid parasites of the genus Leishmania cause a spectrum of w idespread tropical diseases. In the vertebrate host they reside within the macrophage phagolysosome; however, the mechanisms employed in thi s remarkable survival strategy are not well understood. Recent advance s in the molecular genetics of these parasites prompted us to develop methods of functional genetic complementation in Leishmania and apply them to the isolation of genes involved in the biosynthesis of the vir ulence determinant lipophosphoglycan, an abundant glycosyl-phosphatidy linositol-anchored polysaccharide. LPG1, the gene product identified b y complementation of the R2D2 mutant, appears to be a glycosyltransfer ase responsible for the addition of galactofuranosyl residues to the n ascent lipophosphoglycan chain. As galactofuranose is not found in mam malian cells, inhibition of the addition of this sugar could be exploi ted for chemotherapy. Overall, the success of the functional complemen tation approach opens the way to the identification of a variety of ge nes involved in pathogenesis and parasitism.