Reaction of thiosulfate dehydrogenase with a substrate mimic induces dissociation of the cysteine heme ligand giving insight into the mechanism of oxidative catalysis

Jenner, Leon P., Crack, Jason C., Kurth, Julia M., Soldánová, Zuzana, Brandt, Linda, Sokol, Katarzyna P., Reisner, Erwin, Bradley, Justin M., Dahl, Christiane, Cheesman, Myles R. and Butt, Julea N. ORCID: https://orcid.org/0000-0002-9624-5226 (2022) Reaction of thiosulfate dehydrogenase with a substrate mimic induces dissociation of the cysteine heme ligand giving insight into the mechanism of oxidative catalysis. Journal of the American Chemical Society. ISSN 0002-7863

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Abstract

Thiosulfate dehydrogenases are bacterial cytochromes that contribute to the oxidation of inorganic sulfur. The active sites of these enzymes contain low-spin c-type heme with Cys−/His axial ligation. However, the reduction potentials of these hemes are several hundred mV more negative than that of the thiosulfate/tetrathionate couple (Em, +198 mV) making it difficult to rationalize the thiosulfate oxidizing capability. Here, we describe the reaction of Campylobacter jejuni thiosulfate dehydrogenase (TsdA) with sulfite, an analog of thiosulfate. The reaction leads to stoichiometric conversion of the active site Cys to cysteinyl sulfonate (Cα-CH2-S-SO3−) such that the protein exists in a form closely resembling a proposed intermediate in the pathway for thiosulfate oxidation that carries a cysteinyl thiosulfate (Cα-CH2-S-SSO3−). The active site heme in the stable sulfonated protein displays an Em approximately 200 mV more positive than the Cys−/His ligated state. This can explain the thiosulfate oxidizing activity of the enzyme and allows us to propose a catalytic mechanism for thiosulfate oxidation. Substrate driven release of the Cys heme ligand allows that sidechain to provide the site of substrate binding and redox transformation; the neighboring heme then simply provides a site for electron relay to an appropriate partner. This chemistry is distinct from that displayed by the Cys ligated hemes found in gas-sensing hemoproteins and in enzymes such as the cytochromes P450. Thus, a further class of thiolate ligated hemes is proposed as exemplified by the TsdA centers that have evolved to catalyze controlled redox transformations of inorganic oxo anions of sulfur.

Item Type: Article
Additional Information: Funding information: This work was supported by the United Kingdom Biotechnology and Biological Sciences Research Council Grants BB/L022176/1 and BB/K009885/1 (to J.N.B. and M.R.C.), an Engineering and Physical Sciences Research Council DTA Ph.D. studentship (to K.P.S.), an ERC Consolidator Grant “MatEnSAP” 682833 (to E.R.), the European Union’s Horizon 2020 research and innovation programme (project no. 692068 BISON), the Deutsche Forschungsgemeinschaft Grant Da 351/7–2 (to C.D.), and the Aventis Foundation Scholarship 700051 awarded by Stiftung Stipendien-Fonds des Verbandes der Chemischen Industrie (to J.M.K.).
Uncontrolled Keywords: spectroscopy,cyclic voltammetry,heme iron coordination,sulfur cycling,3* ,/dk/atira/pure/researchoutput/REFrank/3_
Faculty \ School: Faculty of Science > School of Chemistry
Faculty of Science > School of Biological Sciences
Depositing User: LivePure Connector
Date Deposited: 16 Sep 2022 13:36
Last Modified: 04 Oct 2022 00:24
URI: https://ueaeprints.uea.ac.uk/id/eprint/88387
DOI: 10.1021/jacs.2c06062

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