Mechanism of Thiosulfate Oxidation in the SoxA Family of Cysteine-ligated Cytochromes

Grabarczyk, Daniel B.; Chappell, Paul E.; Eisel, Bianca; Johnson, Steven; Lea, Susan M.; Berks, Ben C.

doi:10.1074/jbc.m114.618025

Cited by 22 publications

(40 citation statements)

References 40 publications

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“…Each subdomain consists of four ␣-helices surrounding a heme group, the typical class I c-type cytochrome topology. This has been previously reported for the AvTsdA crystal structure (2,12) and is also observed for the M. purpuratum N-terminal TsdB domain. The four subdomains superimpose with r.m.s.d.…”

Section: Overall Fold and Similar Structures Of Mptsdba-supporting

confidence: 62%

“…Nevertheless, some further conclusions regarding the redox activity of AvTsdA can be proposed in light of the crystal structures reported (2,12). The fully oxidized diheme cytochrome AvTsdA contains His/Cys coordination in heme 1 and His/Lys in heme 2.…”

Section: Resultsmentioning

confidence: 99%

“…Characterization of TsdA and TsdB-UV-visible electronic absorbance spectroscopy, X-ray diffraction, and activity assays have revealed a number of characteristic features of AvTsdA (1,2,12). However, the electrochemical window in which the hemes are redox active remained unknown.…”

Section: Resultsmentioning

confidence: 99%

“…8, A, B, and D). Axial ligation by histidine and cysteine is typical for the active site of TsdA proteins (2,12). Indeed, heme 3 exhibits axial ligation by His 291 , and the S␥ atom of Cys 330 is located in close vicinity to the heme iron such that it could serve as the sixth ligand.…”

Section: Overall Fold and Similar Structures Of Mptsdba-mentioning

confidence: 99%

“…an essential intermediate step in the catalytic cycle, possibly involving covalent attachment of a substrate molecule (2,12).…”

Section: Overall Fold and Similar Structures Of Mptsdba-mentioning

confidence: 99%

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

Kurth

Brito

Reuter

et al. 2016

Journal of Biological Chemistry

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Edited by Ruma BanerjeeThe 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 Cys 330 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 ironsulfur protein not only acts as direct electron donor to the reaction center in anoxygenic phototrophs but can also be involved in aerobic respiratory chains.

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Section: Overall Fold and Similar Structures Of Mptsdba-supporting

confidence: 62%

Section: Resultsmentioning

confidence: 99%