Thiosulfate dehydrogenase: a widespread unusual acidophilic c-type cytochrome.
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 M(222) or M(236)) and cysteine (C(123) ) 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 C(123) 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.
Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 168, D-53115 Bonn, Germany.
Kevin
K
Denkmann
Fabian
F
Grein
Renate
R
Zigann
Anna
A
Siemen
Johannes
J
Bergmann
Sebastian
S
van Helmont
Anne
A
Nicolai
Inês A C
IA
Pereira
Christiane
C
Dahl
D000595:Amino Acid Sequence; D002841:Chromatiaceae / Q000201:enzymology* / Q000235:genetics*; D003574:Cytochrome c Group / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics; D016415:Sequence Alignment; D017384:Sequence Deletion
D003574:Cytochrome c Group; D011994:Recombinant Proteins; D010088:Oxidoreductases; C432587:thiosulfate dehydrogenase