Role of Biopterin Transporter (BT1) Gene on Growth and Infectivity of Leishmania

Leishmania are known to be auxotrophic for pteridines that are known to play a critical role in the parasites survival. In the present work the role of biopterin transporter in the growth of the parasite and infectivity in to macrophages has been worked out. The role of biopterin transporter in the susceptibility of Leishmania to antimonial compounds has also been demonstrated. This role has been verified by using attenuated strains of Leishmania with single, double, and triple (null) biopterin (BT1) mutants made by targeted gene replacement with specific antibiotic markers. Growth analysis of these mutants revealed that wild type, single and double knock out cell lines maintained high growth rates in the medium supplemented with biopterin and folate, whereas the triple knock out or null BT1 mutants were unable to grow in the absence of supplemental biopterin. Using wild type and null BT1 mutants, we examined the role of BT1 gene in infectivity and parasite survival. The cell lines with amplified BT1 gene showed increased infectivity and survival in the macrophages where as the cell lines with disrupted BT1 gene showed reduced infectivity and survival in the macrophages. We also examined the interaction between pteridine and antimonial compounds using recombinant Leishmania strains with reduced or absent biopterin transporter gene (BT1) alleles. No difference in susceptibility to Pentostam or Glucantime was observed in both wild type and BT1-knock out strains. However, pterin or folate supplementation resulted in reversal of Glucantime but not Pentostam susceptibility in both wild type and BT1-knock out strains. The reversal of Glucantime susceptibility by pterins in BT1-knock out strains suggests that the effect may be exerted independently of biopterin transporter, possibly by blocking Glucantime uptake.