Publications

• The terminal reductases for selenate and nitrate respiration in Thauera selenatis are two distinct enzymes.

  Rech S.A., Macy J.M.

  A number of approaches have been used to show that a recently isolated selenate-respiring bacterium, Thauera selenatis, is able to synthesize both a selenate reductase (SR) and a nitrate reductase (NR). (i) The pH optimum of the SR was found to be 6.0; that of the NR was 7.0. (ii) The presence of ... >> More

  A number of approaches have been used to show that a recently isolated selenate-respiring bacterium, Thauera selenatis, is able to synthesize both a selenate reductase (SR) and a nitrate reductase (NR). (i) The pH optimum of the SR was found to be 6.0; that of the NR was 7.0. (ii) The presence of nitrate did not inhibit selenate reduction in selenate-grown cells. (iii) In cell extracts, the highest SR or NR activity was observed in cells grown with the respective electron acceptor. (iv) Mutants that were unable to grow with nitrate as the terminal electron acceptor and lacked NR activity were isolated; these mutants grew normally with selenate and synthesized SR. (v) The SR was found in the periplasmic space of the cell, whereas the NR was present in the cytoplasmic membrane. A hypothetical electron transport system involving the SR is described. << Less

  J Bacteriol 174:7316-7320(1992) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Bacterial respiration of arsenic and selenium.

  Stolz J.F., Oremland R.S.

  Oxyanions of arsenic and selenium can be used in microbial anaerobic respiration as terminal electron acceptors. The detection of arsenate and selenate respiring bacteria in numerous pristine and contaminated environments and their rapid appearance in enrichment culture suggest that they are wides ... >> More

  Oxyanions of arsenic and selenium can be used in microbial anaerobic respiration as terminal electron acceptors. The detection of arsenate and selenate respiring bacteria in numerous pristine and contaminated environments and their rapid appearance in enrichment culture suggest that they are widespread and metabolically active in nature. Although the bacterial species that have been isolated and characterized are still few in number, they are scattered throughout the bacterial domain and include Gram-positive bacteria, beta, gamma and epsilon Proteobacteria and the sole member of a deeply branching lineage of the bacteria, Chrysiogenes arsenatus. The oxidation of a number of organic substrates (i.e. acetate, lactate, pyruvate, glycerol, ethanol) or hydrogen can be coupled to the reduction of arsenate and selenate, but the actual donor used varies from species to species. Both periplasmic and membrane-associated arsenate and selenate reductases have been characterized. Although the number of subunits and molecular masses differs, they all contain molybdenum. The extent of the environmental impact on the transformation and mobilization of arsenic and selenium by microbial dissimilatory processes is only now being fully appreciated. << Less

  FEMS Microbiol Rev 23:615-627(1999) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• X-ray absorption spectroscopy of selenate reductase.

  Maher M.J., Santini J., Pickering I.J., Prince R.C., Macy J.M., George G.N.

  The metal sites of selenate reductase from Thauera selenatis have been characterized by Mo, Se, and Fe K-edge X-ray absorption spectroscopy. The Mo site of the oxidized enzyme has 3 to 4 sulfur ligands at 2.33 A from two molybdopterin cofactors, one Mo=O group at 1.68 A and one Mo-O with an interm ... >> More

  The metal sites of selenate reductase from Thauera selenatis have been characterized by Mo, Se, and Fe K-edge X-ray absorption spectroscopy. The Mo site of the oxidized enzyme has 3 to 4 sulfur ligands at 2.33 A from two molybdopterin cofactors, one Mo=O group at 1.68 A and one Mo-O with an intermediate bond length of 1.81 A. The reduced enzyme has a des-oxo active site, again with about four Mo-S ligands (at 2.32 A) and possibly one oxygen ligand at 2.22 A. The enzyme was found to contain Se in a reduced form (probably organic) although the sequence does not indicate the presence of selenocysteine. The Se is coordinated to both a metal (probably Fe) and a lighter scatterer such as carbon. << Less

  Inorg Chem 43:402-404(2004) [PubMed] [EuropePMC]

• Quinol-cytochrome c oxidoreductase and cytochrome c4 mediate electron transfer during selenate respiration in Thauera selenatis.

  Lowe E.C., Bydder S., Hartshorne R.S., Tape H.L., Dridge E.J., Debieux C.M., Paszkiewicz K., Singleton I., Lewis R.J., Santini J.M., Richardson D.J., Butler C.S.

  Selenate reductase (SER) from Thauera selenatis is a periplasmic enzyme that has been classified as a type II molybdoenzyme. The enzyme comprises three subunits SerABC, where SerC is an unusual b-heme cytochrome. In the present work the spectropotentiometric characterization of the SerC component ... >> More

  Selenate reductase (SER) from Thauera selenatis is a periplasmic enzyme that has been classified as a type II molybdoenzyme. The enzyme comprises three subunits SerABC, where SerC is an unusual b-heme cytochrome. In the present work the spectropotentiometric characterization of the SerC component and the identification of redox partners to SER are reported. The mid-point redox potential of the b-heme was determined by optical titration (E(m) + 234 +/-10 mV). A profile of periplasmic c-type cytochromes expressed in T. selenatis under selenate respiring conditions was undertaken. Two c-type cytochromes were purified ( approximately 24 and approximately 6 kDa), and the 24-kDa protein (cytc-Ts4) was shown to donate electrons to SerABC in vitro. Protein sequence of cytc-Ts4 was obtained by N-terminal sequencing and liquid chromatography-tandem mass spectrometry analysis, and based upon sequence similarities, was assigned as a member of cytochrome c(4) family. Redox potentiometry, combined with UV-visible spectroscopy, showed that cytc-Ts4 is a diheme cytochrome with a redox potential of +282 +/-10 mV, and both hemes are predicted to have His-Met ligation. To identify the membrane-bound electron donors to cytc-Ts4, growth of T. selenatis in the presence of respiratory inhibitors was monitored. The specific quinol-cytochrome c oxidoreductase (QCR) inhibitors myxothiazol and antimycin A partially inhibited selenate respiration, demonstrating that some electron flux is via the QCR. Electron transfer via a QCR and a diheme cytochrome c(4) is a novel route for a member of the DMSO reductase family of molybdoenzymes. << Less

  J. Biol. Chem. 285:18433-18442(2010) [PubMed] [EuropePMC]

• Purification and characterization of the selenate reductase from Thauera selenatis.

  Schroeder I., Rech S., Krafft T., Macy J.M.

  Thauera selenatis is one of two isolated bacterial species that can obtain energy by respiring anaerobically with selenate as the terminal electron acceptor. The reduction of selenate to selenite is catalyzed by a selenate reductase, previously shown to be located in the periplasmic space of the c ... >> More

  Thauera selenatis is one of two isolated bacterial species that can obtain energy by respiring anaerobically with selenate as the terminal electron acceptor. The reduction of selenate to selenite is catalyzed by a selenate reductase, previously shown to be located in the periplasmic space of the cell. This study describes the purification of the enzyme from T. selenatis grown anaerobically with selenate. The enzyme is a trimeric alphabetagamma complex with an apparent Mr of 180,000. The alpha, beta, and gamma subunits are 96 kDa, 40 kDa, and 23 kDa, respectively, in size. The selenate reductase contains molybdenum, iron, and acid-labile sulfur as prosthetic group constituents. UV-visible absorption spectroscopy also revealed the presence of one cytochrome b per alphabetagamma complex. The Km for selenate was determined to be 16 microM, and the Vmax was 40 micromol/min/mg of protein. The enzyme is specific for the reduction of selenate; nitrate, nitrite, chlorate, and sulfate were not reduced at detectable rates. These studies constitute the first description of a selenate reductase, which represents a new class of enzymes. The significance of this enzyme in relation to cell growth and energy generation is discussed. << Less

  J. Biol. Chem. 272:23765-23768(1997) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Cloning and sequencing of the genes encoding the periplasmic-cytochrome B-containing selenate reductase of Thauera selenatis.

  Krafft T., Bowen A., Theis F., Macy J.M.

  The periplasmic selenate reductase (Ser) of Thauera selennatis is a component of the electron transport chain catalyzing selenate reduction with acetate as the electron donor (i.e., selenate respiration). The purified enzyme consists of three subunits (SerA, SerB and SerC). Using transposon (i.e., ... >> More

  The periplasmic selenate reductase (Ser) of Thauera selennatis is a component of the electron transport chain catalyzing selenate reduction with acetate as the electron donor (i.e., selenate respiration). The purified enzyme consists of three subunits (SerA, SerB and SerC). Using transposon (i.e., Tn5) mutagenesis selenate reductase mutants were isolated. Junction fragments of DNA adjacent to the integrated Tn5 were used, together with oligonucleotides derived from the N-termini of SerA and SerB, to clone from a gene bank a DNA fragment that contained the corresponding genes. After sequencing, serA, serB and serC were identified by sequence comparison with the N-termini of the three subunits. The genes are arranged in the order serA, serB, serC; a fourth open reading frame (serD) in between, but overlapping serB and serC, is also present. The serA gene product contains an apparent leader peptide with a twin-arginine motif. The remainder of the translated amino acid sequence is similar to that of a number of prokaryotic molybdenum-containing enzymes (e.g., nitrate reductases and formate dehydrogenases of Escherichia coli). The serB gene product contains four cysteine clusters and is similar to various iron-sulfur protein subunits. The serC gene product contains a putative Sec-dependent leader peptide, but there are no similarities between the remainder of the translated protein and other protein subunits. The SerC contains two histidine and four methionine residues, and these may noncovalently bind heme b--which is a component of the active selenate reductase. The serD gene product encodes a putative protein that shows no significant sequence similarities to other proteins. However, the location of the serD within the other ser genes is similar to that of narJ within the E. coli narGHJI operon (nitrate reductase A); thus suggesting that the role of SerD may be similar to that of NarJ, which is a system-specific chaperone protein. << Less

  DNA Seq. 10:365-377(2000) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.