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

Autor: Jenner LP; Centre for Molecular and Structural Biochemistry, School of Chemistry and School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom., Kurth JM; Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich Wilhelms Universität Bonn, D-53115 Bonn, Germany., van Helmont S; Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich Wilhelms Universität Bonn, D-53115 Bonn, Germany., Sokol KP; Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom., Reisner E; Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom., Dahl C; Institut für Mikrobiologie & Biotechnologie, Rheinische Friedrich Wilhelms Universität Bonn, D-53115 Bonn, Germany., Bradley JM; Centre for Molecular and Structural Biochemistry, School of Chemistry and School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom justin.bradley@uea.ac.uk., Butt JN; Centre for Molecular and Structural Biochemistry, School of Chemistry and School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom j.butt@uea.ac.uk., Cheesman MR; Centre for Molecular and Structural Biochemistry, School of Chemistry and School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom m.cheesman@uea.ac.uk.
Jazyk: angličtina
Zdroj: The Journal of biological chemistry [J Biol Chem] 2019 Nov 22; Vol. 294 (47), pp. 18002-18014. Date of Electronic Publication: 2019 Aug 29.
DOI: 10.1074/jbc.RA119.010084
Abstrakt: Thiosulfate dehydrogenases (TsdAs) 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 CD (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 microaerobic 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 ( E m ) 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 E m of +172 mV. In A. vinosum TsdA, Heme 2 reduction triggers a switch from His/Lys ligation ( E m , -129 mV) to His/Met ( E m , +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 E m 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).
(© 2019 Jenner et al.)
Databáze: MEDLINE
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