Authors: Dalia Rokhsana Tao A G Large Morgan C Dienst Marius Retegan Frank Neese
Publish Date: 2016/05/26
Volume: 21, Issue: 4, Pages: 491-499
Abstract
CO dehydrogenase CODH is an environmentally crucial bacterial enzyme that oxidizes CO to CO2 at a Mo–Cu active site Despite the close to atomic resolution structure 11 Å significant uncertainties have remained with regard to the protonation state of the waterderived equatorial ligand coordinated at the Mocenter as well as the nature of intermediates formed during the catalytic cycle To address the protonation state of the equatorial ligand we have developed a realistic in silico QM model ~179 atoms containing structurally essential residues surrounding the active site Using our QM model we examined each plausible combination of redox states MoVI–CuI MoV–CuII MoV–CuI and MoIV–CuI and Mocoordinated equatorial ligands O2− OH− H2O as well as the effects of secondsphere residues surrounding the active site Herein we present a refined computational model for the MoVI state in which Glu763 acts as an active site base leading to a MoO2like core and a protonated Glu763 Calculated structural and spectroscopic data hyperfine couplings are in support of a MoO2like core in agreement with XRD data The calculated twoelectron reduction potential E = −467 mV vs SHE is in reasonable agreement with the experimental value E = −558 mV vs SHE for the redox couple comprising an equatorial oxo ligand and protonated Glu763 in the MoVI–CuI state and an equatorial water in the MoIV–CuI state We also suggest a potential role of secondsphere residues eg Glu763 Phe390 based on geometric changes observed upon exclusion of these residues in the most plausible oxidized statesThis research was funded by generous financial contributions from Whitman College and the M J Murdock Charitable Trust Special thanks to Dr Robert Szilagyi Montana State University Bozeman MT for his tremendous assistance in setting up the computational server at Whitman College and for providing comments and feedback during the preparation of this manuscript We gratefully acknowledge the Max Planck Society for financial support of this work
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