Heme ligation and redox chemistry in two bacterial thiosulfate dehydrogenase (TsdA) enzyme

Jenner, Leon P., Kurth, Julia M., van Helmont, Sebastian, Sokol, Katarzyna P., Reisner, Erwin, Dahl, Christiane, Bradley, Justin M., Butt, Julea N. ORCID: https://orcid.org/0000-0002-9624-5226 and Cheesman, Myles (2019) Heme ligation and redox chemistry in two bacterial thiosulfate dehydrogenase (TsdA) enzyme. Journal of Biological Chemistry, 294 (47). pp. 18002-18014. ISSN 0021-9258

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Abstract

Thiosulfate dehydrogenases (TsdA) are bidirectional bacterial di-heme enzymes that catalyze the interconversion of tetrathionate and thiosulfate at measurable rates in both directions. In contrast to our knowledge of TsdA activities, information on the redox properties in the absence of substrates is rather scant. To address this deficit, we combined magnetic circular dichroism (MCD) spectroscopy and protein film electrochemistry (PFE) in a study to resolve heme ligation and redox chemistry in two representative TsdAs. We examined the TsdAs from Campylobacter jejuni, a micro-aerobe human pathogen, and from the purple sulfur bacterium Allochromatium vinosum. In these organisms, the enzyme functions as a tetrathionate reductase and a thiosulfate oxidase respectively. The active site Heme 1 in both enzymes has His/Cys− ligation in the ferric and ferrous states and the midpoint potentials (Em) of the corresponding redox transformations are similar, −185 mV versus standard hydrogen electrode (SHE). However, fundamental differences are observed in the properties of the second, electron transferring, Heme 2. In C. jejuni TsdA Heme 2 has His/Met ligation and an Em of +172 mV. In A. vinosum TsdA, Heme 2 reduction triggers a switch from His/Lys ligation (Em, −129 mV) to His/Met (Em,+266 mV) but the rates of interconversion are such that His/Lys ligation would be retained during turnover. In summary, our findings have unambiguously assigned Em values to defined axial ligand sets in TsdAs, specified the rates of Heme 2 ligand exchange in the A. vinosum enzyme, and provided information relevant to describing their catalytic mechanism(s).

Item Type:	Article
Faculty \ School:	Faculty of Science > School of Chemistry (former - to 2024) Faculty of Science > School of Biological Sciences
UEA Research Groups:	Faculty of Science > Research Groups > Molecular Microbiology Faculty of Science > Research Groups > Chemistry of Light and Energy Faculty of Science > Research Groups > Chemistry of Life Processes Faculty of Science > Research Centres > Centre for Molecular and Structural Biochemistry Faculty of Science > Research Groups > Energy Materials Laboratory
Depositing User:	LivePure Connector
Date Deposited:	02 Sep 2019 15:36
Last Modified:	25 Sep 2024 14:15
URI:	https://ueaeprints.uea.ac.uk/id/eprint/72086
DOI:	10.1074/jbc.RA119.010084

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