Tejada-Jiménez Manuel, Llamas Angel, Sanz-Luque Emanuel, Galván Aurora, Fernández Emilio
Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Córdoba, Campus de Rabanales, Edif. Severo Ochoa, 14071 Córdoba, Spain.
Proc Natl Acad Sci U S A. 2007 Dec 11;104(50):20126-30. doi: 10.1073/pnas.0704646104. Epub 2007 Dec 5.
Molybdenum is an essential element for almost all living beings, which, in the form of a molybdopterin-cofactor, participates in the active site of enzymes involved in key reactions of carbon, nitrogen, and sulfur metabolism. This metal is taken up by cells in form of the oxyanion molybdate. Bacteria acquire molybdate by an ATP-binding-cassette (ABC) transport system in a widely studied process, but how eukaryotic cells take up molybdenum is unknown because molybdate transporters have not been identified so far. Here, we report a eukaryotic high-affinity molybdate transporter, encoded by the green alga Chlamydomonas reinhardtii gene MoT1. An antisense RNA strategy over the MoT1 gene showed that interference of the expression of this gene leads to the inhibition of molybdate transport activity and, in turn, of the Mo-containing enzyme nitrate reductase, indicating a function of MoT1 in molybdate transport. MOT1 functionality was also shown by heterologous expression in Saccharomyces cerevisiae. Molybdate uptake mediated by MOT1 showed a K(m) of approximately 6 nM, which is the range of the lowest K(m) values reported and was activated in the presence of nitrate. Analysis of deduced sequence from the putative protein coded by MoT1 showed motifs specifically conserved in similar proteins present in the databases, and defines a family of membrane proteins in both eukaryotes and prokaryotes probably involved in molybdate transport and distantly related to plant sulfate transporters SULTR. These findings represent an important step in the understanding of molybdate transport, a crucial process in eukaryotic cells.
钼是几乎所有生物的必需元素，它以钼蝶呤辅因子的形式参与碳、氮和硫代谢关键反应中酶的活性位点。这种金属以钼酸根阴离子的形式被细胞摄取。细菌通过一种广泛研究的ATP结合盒（ABC）转运系统获取钼酸根，但真核细胞如何摄取钼尚不清楚，因为迄今为止尚未鉴定出钼酸根转运蛋白。在此，我们报道了一种由绿藻莱茵衣藻基因MoT1编码的真核高亲和力钼酸根转运蛋白。针对MoT1基因的反义RNA策略表明，该基因表达的干扰会导致钼酸根转运活性的抑制，进而抑制含钼酶硝酸还原酶，这表明MoT1在钼酸根转运中具有功能。在酿酒酵母中的异源表达也显示了MOT1的功能。由MOT1介导的钼酸根摄取的K(m)约为6 nM，这是报道的最低K(m)值范围，并且在硝酸盐存在下被激活。对MoT1编码的推定蛋白质推导序列的分析显示，在数据库中存在的类似蛋白质中特定保守的基序，并定义了真核生物和原核生物中可能参与钼酸根转运且与植物硫酸盐转运蛋白SULTR远缘相关的一类膜蛋白。这些发现代表了在理解钼酸根转运这一真核细胞关键过程方面的重要一步。
