Present address: Institut für Medizinische Mikrobiologie, Immunologie & Parasitologie, Abteilung Pharmazeutische Mikrobiologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 168, D-53115 Bonn, Germany.
Thiosulfate dehydrogenase: a widespread unusual acidophilic c-type cytochrome
Article first published online: 11 JUL 2012
© 2012 Society for Applied Microbiology and Blackwell Publishing Ltd
Thematic issue: Sulfur Metabolism
Volume 14, Issue 10, pages 2673–2688, October 2012
How to Cite
Denkmann, K., Grein, F., Zigann, R., Siemen, A., Bergmann, J., van Helmont, S., Nicolai, A., Pereira, I. A. C. and Dahl, C. (2012), Thiosulfate dehydrogenase: a widespread unusual acidophilic c-type cytochrome. Environmental Microbiology, 14: 2673–2688. doi: 10.1111/j.1462-2920.2012.02820.x
- Issue published online: 3 OCT 2012
- Article first published online: 11 JUL 2012
- Accepted manuscript online: 15 JUN 2012 03:27AM EST
- Received 15 February, 2012; revised 6 June, 2012; accepted 10 June, 2012.
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.