Publications

• Tetrathionate stimulated growth of Campylobacter jejuni identifies a new type of bi-functional tetrathionate reductase (TsdA) that is widely distributed in bacteria.

  Liu Y.W., Denkmann K., Kosciow K., Dahl C., Kelly D.J.

  Tetrathionate (S4 O6 (2-) ) is used by some bacteria as an electron acceptor and can be produced in the vertebrate intestinal mucosa from the oxidation of thiosulphate (S2 O3 (2-) ) by reactive oxygen species during inflammation. Surprisingly, growth of the microaerophilic mucosal pathogen Campylo ... >> More

  Tetrathionate (S4 O6 (2-) ) is used by some bacteria as an electron acceptor and can be produced in the vertebrate intestinal mucosa from the oxidation of thiosulphate (S2 O3 (2-) ) by reactive oxygen species during inflammation. Surprisingly, growth of the microaerophilic mucosal pathogen Campylobacter jejuni under oxygen-limited conditions was stimulated by tetrathionate, although it does not possess any known type of tetrathionate reductase. Here, we identify a dihaem cytochrome c (C8j_0815; TsdA) as the enzyme responsible. Kinetic studies with purified recombinant C. jejuni TsdA showed it to be a bifunctional tetrathionate reductase/thiosulphate dehydrogenase with a high affinity for tetrathionate. A tsdA null mutant still slowly reduced, but could not grow on, tetrathionate under oxygen limitation, lacked thiosulphate-dependent respiration and failed to convert thiosulphate to tetrathionate microaerobically. A TsdA paralogue (C8j_0040), lacking the unusual His-Cys haem ligation of TsdA, had low thiosulphate dehydrogenase and tetrathionate reductase activities. Our data highlight a hitherto unrecognized capacity of C. jejuni to use tetrathionate and thiosulphate in its energy metabolism, which may promote growth in the host. Moreover, as TsdA represents a new class of tetrathionate reductase that is widely distributed among bacteria, we predict that energy conserving tetrathionate respiration is far more common than currently appreciated. << Less

  Mol Microbiol 88:173-188(2013) [PubMed] [EuropePMC]

• Thiosulfate dehydrogenase (TsdA) from Allochromatium vinosum: structural and functional insights into thiosulfate oxidation.

  Brito J.A., Denkmann K., Pereira I.A., Archer M., Dahl C.

  Although the oxidative condensation of two thiosulfate anions to tetrathionate constitutes a well documented and significant part of the natural sulfur cycle, little is known about the enzymes catalyzing this reaction. In the purple sulfur bacterium Allochromatium vinosum, the reaction is catalyze ... >> More

  Although the oxidative condensation of two thiosulfate anions to tetrathionate constitutes a well documented and significant part of the natural sulfur cycle, little is known about the enzymes catalyzing this reaction. In the purple sulfur bacterium Allochromatium vinosum, the reaction is catalyzed by the periplasmic diheme c-type cytochrome thiosulfate dehydrogenase (TsdA). Here, we report the crystal structure of the "as isolated" form of A. vinosum TsdA to 1.98 Å resolution and those of several redox states of the enzyme to different resolutions. The protein contains two typical class I c-type cytochrome domains wrapped around two hemes axially coordinated by His(53)/Cys(96) and His(164)/Lys(208). These domains are very similar, suggesting a gene duplication event during evolution. A ligand switch from Lys(208) to Met(209) is observed upon reduction of the enzyme. Cys(96) is an essential residue for catalysis, with the specific activity of the enzyme being completely abolished in several TsdA-Cys(96) variants. TsdA-K208N, K208G, and M209G variants were catalytically active in thiosulfate oxidation as well as in tetrathionate reduction, pointing to heme 2 as the electron exit point. In this study, we provide spectroscopic and structural evidence that the TsdA reaction cycle involves the transient presence of heme 1 in the high-spin state caused by movement of the Sγ atom of Cys(96) out of the iron coordination sphere. Based on the presented data, we draw important conclusions about the enzyme and propose a possible reaction mechanism for TsdA. << Less

  J Biol Chem 290:9222-9238(2015) [PubMed] [EuropePMC]

• Electron Accepting Units of the Diheme Cytochrome c TsdA, a Bifunctional Thiosulfate Dehydrogenase/Tetrathionate Reductase.

  Kurth J.M., Brito J.A., Reuter J., Flegler A., Koch T., Franke T., Klein E.M., Rowe S.F., Butt J.N., Denkmann K., Pereira I.A., Archer M., Dahl C.

  The enzymes of the thiosulfate dehydrogenase (TsdA) family are wide-spread diheme c-type cytochromes. Here, redox carriers were studied mediating the flow of electrons arising from thiosulfate oxidation into respiratory or photosynthetic electron chains. In a number of organisms, including Thiomon ... >> More

  The enzymes of the thiosulfate dehydrogenase (TsdA) family are wide-spread diheme c-type cytochromes. Here, redox carriers were studied mediating the flow of electrons arising from thiosulfate oxidation into respiratory or photosynthetic electron chains. In a number of organisms, including Thiomonas intermedia and Sideroxydans lithotrophicus, the tsdA gene is immediately preceded by tsdB encoding for another diheme cytochrome. Spectrophotometric experiments in combination with enzymatic assays in solution showed that TsdB acts as an effective electron acceptor of TsdA in vitro when TsdA and TsdB originate from the same source organism. Although TsdA covers a range from -300 to +150 mV, TsdB is redox active between -100 and +300 mV, thus enabling electron transfer between these hemoproteins. The three-dimensional structure of the TsdB-TsdA fusion protein from the purple sulfur bacterium Marichromatium purpuratum was solved by X-ray crystallography to 2.75 Å resolution providing insights into internal electron transfer. In the oxidized state, this tetraheme cytochrome c contains three hemes with axial His/Met ligation, whereas heme 3 exhibits the His/Cys coordination typical for TsdA active sites. Interestingly, thiosulfate is covalently bound to Cys³³⁰ on heme 3. In several bacteria, including Allochromatium vinosum, TsdB is not present, precluding a general and essential role for electron flow. Both AvTsdA and the MpTsdBA fusion react efficiently in vitro with high potential iron-sulfur protein from A. vinosum (E_m +350 mV). High potential iron-sulfur protein not only acts as direct electron donor to the reaction center in anoxygenic phototrophs but can also be involved in aerobic respiratory chains. << Less

  J Biol Chem 291:24804-24818(2016) [PubMed] [EuropePMC]

• Thiosulfate dehydrogenase: a widespread unusual acidophilic c-type cytochrome.

  Denkmann K., Grein F., Zigann R., Siemen A., Bergmann J., van Helmont S., Nicolai A., Pereira I.A., Dahl C.

  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 cyt ... >> More

  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. << Less

  Environ. Microbiol. 14:2673-2688(2012) [PubMed] [EuropePMC]

• Thiosulphate oxidation in the phototrophic sulphur bacterium Allochromatium vinosum.

  Hensen D., Sperling D., Trueper H.G., Brune D.C., Dahl C.

  Two different pathways for thiosulphate oxidation are present in the purple sulphur bacterium Allochromatium vinosum: oxidation to tetrathionate and complete oxidation to sulphate with obligatory formation of sulphur globules as intermediates. The tetrathionate:sulphate ratio is strongly pH-depend ... >> More

  Two different pathways for thiosulphate oxidation are present in the purple sulphur bacterium Allochromatium vinosum: oxidation to tetrathionate and complete oxidation to sulphate with obligatory formation of sulphur globules as intermediates. The tetrathionate:sulphate ratio is strongly pH-dependent with tetrathionate formation being preferred under acidic conditions. Thiosulphate dehydrogenase, a constitutively expressed monomeric 30 kDa c-type cytochrome with a pH optimum at pH 4.2 catalyses tetrathionate formation. A periplasmic thiosulphate-oxidizing multienzyme complex (Sox) has been described to be responsible for formation of sulphate from thiosulphate in chemotrophic and phototrophic sulphur oxidizers that do not form sulphur deposits. In the sulphur-storing A. vinosum we identified five sox genes in two independent loci (soxBXA and soxYZ). For SoxA a thiosulphate-dependent induction of expression, above a low constitutive level, was observed. Three sox-encoded proteins were purified: the heterodimeric c-type cytochrome SoxXA, the monomeric SoxB and the heterodimeric SoxYZ. Gene inactivation and complementation experiments proved these proteins to be indispensable for thiosulphate oxidation to sulphate. The intermediary formation of sulphur globules in A. vinosum appears to be related to the lack of soxCD genes, the products of which are proposed to oxidize SoxY-bound sulphane sulphur. In their absence the latter is instead transferred to growing sulphur globules. << Less

  Mol. Microbiol. 62:794-810(2006) [PubMed] [EuropePMC]

  This publication is cited by 4 other entries.