Bébien Magali, Kirsch Julia, Méjean Vincent, Verméglio André
CEA/Cadarache-DSV-DEVM-Laboratoire de Bioénergétique Cellulaire, Université de la Méditerranée CEA 1000, 13108 Saint-Paul-lez-Durance Cedex, France1.
Laboratoire de Chimie Bactérienne, Institut de Biologie Structurale et Microbiologie, CNRS, 31 Chemin Joseph Aiguier, BP 71, 13402 Marseille Cedex 20, France2.
Microbiology (Reading). 2002 Dec;148(Pt 12):3865-3872. doi: 10.1099/00221287-148-12-3865.
Selenium oxyanions, particularly selenite, can be highly toxic to living organisms. Few bacteria reduce both selenate and selenite into the less toxic elemental selenium. Insights into the mechanisms of the transport and the reduction of selenium oxyanions in Escherichia coli were provided by a genetic analysis based on transposon mutagenesis. Ten mutants impaired in selenate reduction were analysed. Three of them were altered in genes encoding transport proteins including a porin, an inner-membrane protein and a sulfate carrier. Two mutants were altered in genes required for molybdopterin biosynthesis, strongly suggesting that the selenate reductase of E. coli is a molybdoenzyme. However, mutants deleted in various oxomolybdenum enzymes described so far in this species still reduced selenate. Finally, a mutant in the gene ygfK encoding a putative oxidoreductase was obtained. This gene is located upstream of ygfN and ygfM in the ygfKLMN putative operon. YgfN and YgfM code for a molybdopterin-containing enzyme and a polypeptide carrying a FAD domain, respectively. It is therefore proposed that the selenate reductase of E. coli is a structural complex including the proteins YgfK, YgfM and YgfN. In addition, all the various mutants were still able to reduce selenite into elemental selenium. This implies that the transport and reduction of this compound are clearly distinct from those of selenate.
硒含氧阴离子，尤其是亚硒酸盐，对生物体可能具有高毒性。很少有细菌能将硒酸盐和亚硒酸盐都还原为毒性较低的元素硒。基于转座子诱变的遗传分析为深入了解大肠杆菌中硒含氧阴离子的转运和还原机制提供了线索。分析了10个在硒酸盐还原方面受损的突变体。其中3个在编码转运蛋白的基因中发生了改变，这些转运蛋白包括一种孔蛋白、一种内膜蛋白和一种硫酸盐载体。两个突变体在钼蝶呤生物合成所需的基因中发生了改变，这强烈表明大肠杆菌的硒酸盐还原酶是一种钼酶。然而，在该物种中迄今为止描述的各种含氧化钼酶缺失的突变体仍然能够还原硒酸盐。最后，获得了一个在编码假定氧化还原酶的ygfK基因中的突变体。该基因位于ygfKLMN假定操纵子中ygfN和ygfM的上游。YgfN和YgfM分别编码一种含钼蝶呤的酶和一种带有FAD结构域的多肽。因此，有人提出大肠杆菌的硒酸盐还原酶是一种结构复合物，包括YgfK、YgfM和YgfN蛋白。此外，所有不同的突变体仍然能够将亚硒酸盐还原为元素硒。这意味着这种化合物的转运和还原与硒酸盐的明显不同。
