Involvement of a putative molybdenum enzyme in the reduction of selenate by Escherichia coli.
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.
Bébien
Magali
M
CEA/Cadarache-DSV-DEVM-Laboratoire de Bioénergétique Cellulaire, Université de la Méditerranée CEA 1000, 13108 Saint-Paul-lez-Durance Cedex, France1.
Kirsch
Julia
J
CEA/Cadarache-DSV-DEVM-Laboratoire de Bioénergétique Cellulaire, Université de la Méditerranée CEA 1000, 13108 Saint-Paul-lez-Durance Cedex, France1.
Méjean
Vincent
V
Laboratoire de Chimie Bactérienne, Institut de Biologie Structurale et Microbiologie, CNRS, 31 Chemin Joseph Aiguier, BP 71, 13402 Marseille Cedex 20, France2.
Verméglio
André
A
CEA/Cadarache-DSV-DEVM-Laboratoire de Bioénergétique Cellulaire, Université de la Méditerranée CEA 1000, 13108 Saint-Paul-lez-Durance Cedex, France1.
D003067:Coenzymes; D004251:DNA Transposable Elements; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D008667:Metalloproteins / Q000235:genetics / Q000378:metabolism*; D000090006:Molybdenum Cofactors; D016254:Mutagenesis, Insertional; D009876:Operon; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D011621:Pteridines / Q000378:metabolism*; D064586:Selenic Acid; D018036:Selenium Compounds / Q000378:metabolism*; D018038:Sodium Selenite / Q000378:metabolism
D003067:Coenzymes; D004251:DNA Transposable Elements; D029968:Escherichia coli Proteins; D008667:Metalloproteins; D000090006:Molybdenum Cofactors; D010088:Oxidoreductases; D011621:Pteridines; D064586:Selenic Acid; D018036:Selenium Compounds; D018038:Sodium Selenite; C022261:molybdopterin; C078108:selenate reductase