PRENYLATION OF PROTEINS IN TRYPANOSOMA-BRUCEI

Prenyl modification of proteins by farnesyl and geranylgeranyl isopren oids occurs in a variety of eukaryotic cells. Culturing of Trypanosoma brucei in the presence of [H-3]mevalonolactone (which is hydrolyzed i n cells to give mevalonic acid, the precursor of protein prenyl groups ) and an inhibitor of mevalonic acid biosynthesis leads to the radiola beling of a specific set of proteins when analyzed by gel electrophore sis. T. brucei proteins were also labeled when cells were cultured in the presence of [H-3]farnesol or [H-3]geranylgeraniol, and each prenol labels a distinct set of proteins. Unlike mammalian cells, only a few T. brucei proteins of molecular weights similar to those of the mamma lian Pas superfamily of GTPase (20-30 kDa) were labeled with [H-3]farn esol or [H-3]geranylgeraniol. When the 0-55% ammonium sulfate fraction of T. brucei cytosol was fractionated on anion exchange chromatograph y, protein farnesyltransferase (PFT) and protein geranylgeranyltransfe rase-I (PGGT-I) activities were detected and elute as two distinct pea ks. Partially purified T. brucei PFT and PGGT-I display partly differe nt specificities toward prenyl acceptor substrates from those of mamma lian protein prenyltransferases. As shown previously, rat PFT utilizes proteins ending in CVLS and CVIM as efficient prenyl accepters and ra t PGGT-I utilizes proteins ending in CVLL and CVIM in vitro. On the co ntrary, T. brucei PFT farnesylates a protein ending in CVIM but not CV LS or CVLL, and T. brucei PGGT-I preferentially geranylgeranylates a p rotein ending in CVLL. (C) 1997 Elsevier Science B.V.