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Thiosulfate dehydrogenase: a widespread unusual acidophilic c-type cytochrome

Authors

  • Kevin Denkmann,

    1. Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 168, D-53115 Bonn, Germany
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  • Fabian Grein,

    1. Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 168, D-53115 Bonn, Germany
    2. Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Avenida da Republica, EAN, Apt. 127, 2780-157 Oeiras, Portugal.
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    • Present address: Institut für Medizinische Mikrobiologie, Immunologie & Parasitologie, Abteilung Pharmazeutische Mikrobiologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 168, D-53115 Bonn, Germany.

  • Renate Zigann,

    1. Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 168, D-53115 Bonn, Germany
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  • Anna Siemen,

    1. Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 168, D-53115 Bonn, Germany
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  • Johannes Bergmann,

    1. Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 168, D-53115 Bonn, Germany
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  • Sebastian van Helmont,

    1. Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 168, D-53115 Bonn, Germany
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  • Anne Nicolai,

    1. Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 168, D-53115 Bonn, Germany
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  • Inês A. C. Pereira,

    1. Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Avenida da Republica, EAN, Apt. 127, 2780-157 Oeiras, Portugal.
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  • Christiane Dahl

    Corresponding author
    1. Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 168, D-53115 Bonn, Germany
      E-mail chdahl@uni-bonn.de; Tel. (+49) 228 732119; Fax (+49) 228 737576.
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E-mail chdahl@uni-bonn.de; Tel. (+49) 228 732119; Fax (+49) 228 737576.

Summary

In this work we identified the gene for the tetrathionate-forming thiosulfate dehydrogenase (TsdA) from the purple sulfur bacterium Allochromatium vinosum by sequence analysis and reverse genetics. The recombinant protein produced in Escherichia coli is a periplasmic, monomeric 25.8 kDa dihaem cytochrome c with an enzyme activity optimum at pH 4. UV-visible and electron paramagnetic resonance spectroscopy indicate methionine (strictly conserved M222 or M236) and cysteine (C123) as probable sixth distal axial ligands of the two haem irons in TsdA. These results place TsdA in the group of c-type cytochromes with an unusual axial histidine-cysteine coordination of the haem iron. These proteins appear to play a pivotal role in sulfur-based energy metabolism. Exchange of C123 to glycine rendered thiosulfate dehydrogenase inactive, proving the importance of this residue for catalysis.

TsdA homologues are present in α-, β-, δ-, γ- and ε-Proteobacteria. Three of these were produced in E. coli and exhibited the expected enzymatic activity. The widespread occurrence of tsdA agrees with reports of tetrathionate formation not only by specialized sulfur oxidizers but also by many chemoorganoheterotrophs that use thiosulfate as a supplemental but not as the sole energy source.

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