Richard Dave, Kündig Christoph, Ouellette Marc
Centre de Recherche en Infectiologie du Centre de Recherche du CHUL and Division de Microbiologie, Faculté de Médecine, Université Laval, Québec G1V 4G2, Canada.
J Biol Chem. 2002 Aug 16;277(33):29460-7. doi: 10.1074/jbc.M204796200. Epub 2002 May 22.
The protozoan parasite Leishmania is a folate auxotroph and thus depends on the uptake of folate from the environment to meet its folate requirement. We show here that Leishmania contains several putative pteridine transporter genes. Some of these genes are deleted in methotrexate-resistant Leishmania cells where there is no measurable uptake of methotrexate. Transport studies suggest that Leishmania has more than one active folate transporter, and one of these, named FT5, corresponds to a very high affinity folate transporter (K(m) 84 nm). The uptake of both folate and methotrexate was impaired in an FT5 null mutant at low substrate concentrations (50 nm), although transport properties at higher concentrations (1000 nm) were not statistically different between wild-type and the FT5 null mutant. Modulation of the expression of FT5 also changes the susceptibility of Leishmania cells to methotrexate. These results have permitted the characterization of a novel class of folate transporters and suggest that the parasite Leishmania has several gene products possibly transporting folates and related molecules under varying conditions.
原生动物寄生虫利什曼原虫是一种叶酸营养缺陷型生物，因此依赖于从环境中摄取叶酸来满足其叶酸需求。我们在此表明，利什曼原虫含有几个假定的蝶啶转运蛋白基因。其中一些基因在耐甲氨蝶呤的利什曼原虫细胞中缺失，在这些细胞中没有可测量的甲氨蝶呤摄取。转运研究表明，利什曼原虫有不止一种活性叶酸转运蛋白，其中一种名为FT5，对应一种非常高亲和力的叶酸转运蛋白（K(m) 84纳米）。在低底物浓度（50纳米）下，FT5基因敲除突变体中叶酸和甲氨蝶呤的摄取均受损，尽管在较高浓度（1000纳米）下，野生型和FT5基因敲除突变体之间的转运特性在统计学上没有差异。FT5表达的调节也会改变利什曼原虫细胞对甲氨蝶呤的敏感性。这些结果使得能够对一类新型叶酸转运蛋白进行表征，并表明寄生虫利什曼原虫有几种基因产物可能在不同条件下转运叶酸和相关分子。
