*Max F. Perutz Laboratories, Department of Microbiology, Immunology and Genetics, University of Vienna, Dr. Bohrgasse 9, A-1030 Vienna, Austria.
Biochem J. 2013 Oct 1;455(1):57-65. doi: 10.1042/BJ20130144.
Mitochondrial iron uptake is of key importance both for organelle function and cellular iron homoeostasis. The mitochondrial carrier family members Mrs3 and Mrs4 (homologues of vertebrate mitoferrin) function in organellar iron supply, yet other low efficiency transporters may exist. In Saccharomyces cerevisiae, overexpression of RIM2 (MRS12) encoding a mitochondrial pyrimidine nucleotide transporter can overcome the iron-related phenotypes of strains lacking both MRS3 and MRS4. In the present study we show by in vitro transport studies that Rim2 mediates the transport of iron and other divalent metal ions across the mitochondrial inner membrane in a pyrimidine nucleotide-dependent fashion. Mutations in the proposed substrate-binding site of Rim2 prevent both pyrimidine nucleotide and divalent ion transport. These results document that Rim2 catalyses the co-import of pyrimidine nucleotides and divalent metal ions including ferrous iron. The deletion of RIM2 alone has no significant effect on mitochondrial iron supply, Fe-S protein maturation and haem synthesis. However, RIM2 deletion in mrs3/4Δ cells aggravates their Fe-S protein maturation defect. We conclude that under normal physiological conditions Rim2 does not play a significant role in mitochondrial iron acquisition, yet, in the absence of the main iron transporters Mrs3 and Mrs4, this carrier can supply the mitochondrial matrix with iron in a pyrimidine-nucleotide-dependent fashion.
线粒体铁摄取对于细胞器功能和细胞铁稳态都至关重要。线粒体载体家族成员 Mrs3 和 Mrs4（脊椎动物 mitoferrin 的同源物）在细胞器铁供应中发挥作用，但可能存在其他低效率的转运蛋白。在酿酒酵母中，过量表达编码线粒体嘧啶核苷酸转运体的 Rim2（MRS12）可以克服缺乏 Mrs3 和 Mrs4 的菌株的铁相关表型。在本研究中，我们通过体外转运研究表明，Rim2 以嘧啶核苷酸依赖性方式介导铁和其他二价金属离子穿过线粒体内膜的转运。Rim2 中假定的底物结合位点的突变阻止嘧啶核苷酸和二价离子的转运。这些结果表明 Rim2 催化嘧啶核苷酸和包括亚铁在内的二价金属离子的共输入。单独删除 Rim2 对线粒体铁供应、Fe-S 蛋白成熟和血红素合成没有显著影响。然而，在 mrs3/4Δ 细胞中删除 Rim2 会加重它们的 Fe-S 蛋白成熟缺陷。我们得出结论，在正常生理条件下，Rim2 在线粒体铁摄取中不起重要作用，但在主要铁转运蛋白 Mrs3 和 Mrs4 缺失的情况下，这种载体可以以嘧啶核苷酸依赖性方式为线粒体基质提供铁。
