Characterization of the folylpolyglutamate synthetase gene and polyglutamylation of folates in the protozoan parasite Leishmania.

Folates are polyglutamylated in most organisms by the enzyme folylpolyglutamate synthetase (FPGS). The Leishmania tarentolae FPGS gene was isolated. Its predicted product contains 538 amino acids and shows 33 and 30% identity with the human and yeast FPGS proteins, respectively. The level of folate polygtutamylation was studied in L. tarentolae promastigotes and in Leishmania infantum promastigotes and axenic amastigotes. In all species examined, folates were found predominantly as pentaglutamates, although monoglutamates were found in higher proportion in L. infantum axenic amastigote cells. Leishmania cells transfected with a FPGS containing plasmid (FPGS transfectant) exhibited a 6-fold increase in FPGS activity (32.7 pmol mg(-1) h(-1)) compared with wild-type cells (4.7 pmol mg(-1) h(-1)). HPLC analysis of the polyglutamylated forms of folates indicated a 2-fold increase of hexaglutamates in the FPGS transfectant compared with wild-type cells, while cells with one FPGS allele interrupted showed a higher proportion of short chain glutamates. The long-term accumulation of folates was greatly increased in the FPGS transfectant. Overall, this work indicates that FPGS activity is expressed in all forms of the parasite, and modulates the retention of folate, thereby possibly playing an important role in physiology.