Molecular analysis of the trimethylamine N-oxide (TMAO) reductase respiratory system from a Shewanella species.
Trimethylamine N-oxide (TMAO) is an abundant compound of tissues of marine fish and invertebrates. During fish spoilage, certain marine bacteria can reduce TMAO to nauseous trimethylamine (TMA). One such bacterium has been isolated and identified as a new Shewanella species, and called Shewanella massilia. The anaerobic growth of S. massilia is greatly increased when TMAO is added, indicating that TMAO reduction involves a respiratory pathway. The TorA enzyme responsible for TMAO reduction is a molybdenum cofactor-containing protein of 90 kDa located in the periplasm. Whereas TorA is induced by both TMAO and dimethylsulfoxide (DMSO), this enzyme has a high substrate specificity and appears to only efficiently reduce TMAO as a natural compound. The structural torA gene encoding the TMAO reductase (TorA) and its flanking regions were amplified using PCR techniques. The torA gene is the third gene of a TMAO-inducible operon (torECAD) encoding the TMAO respiratory components. The torC gene, located upstream from torA encodes a pentahemic c-type cytochrome, likely to be involved in electron transfer to the TorA terminal reductase. TorC was shown to be anchored to the membrane and, like TorA, is induced by TMAO. Except for the TorE protein, which is encoded by the first gene of the torECAD operon, all the tor gene products are homologous to proteins found in the TMAO/DMSO reductase systems from Escherichia coli and Rhodobacter species. In addition, the genetic organization of these systems is similar. Although these bacteria are found in different ecological niches, their respiratory systems appear to be phylogenetically related, suggesting that they come from a common ancestor.
Dos Santos
J P
JP
Institut de Biologie Structurale et Microbiologie, Centre National de la Recherche Scientifique, 31, chemin Joseph Aiguier, Marseille Cedex 20, 13402, France.
Iobbi-Nivol
C
C
Couillault
C
C
Giordano
G
G
Méjean
V
V
D000595:Amino Acid Sequence; D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D003067:Coenzymes; D003574:Cytochrome c Group / Q000235:genetics*; D004579:Electron Transport; D004790:Enzyme Induction; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D006092:Gram-Negative Facultatively Anaerobic Rods / Q000201:enzymology / Q000235:genetics*; D008386:Marine Biology; D008667:Metalloproteins; D008744:Methylamines / Q000378:metabolism*; D008969:Molecular Sequence Data; D008982:Molybdenum; D000090006:Molybdenum Cofactors; D009876:Operon; D010089:Oxidoreductases, N-Demethylating / Q000235:genetics* / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011621:Pteridines; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
D001426:Bacterial Proteins; D003067:Coenzymes; D003574:Cytochrome c Group; D029968:Escherichia coli Proteins; D008667:Metalloproteins; D008744:Methylamines; D008982:Molybdenum; D000090006:Molybdenum Cofactors; D010089:Oxidoreductases, N-Demethylating; D011621:Pteridines; C088082:TorC protein, E coli; C022261:molybdopterin; C023186:trimethylamine dehydrogenase; C005855:trimethyloxamine