Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 112, Issue 47, Pages 14506-14511Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1516869112
Keywords
Fourier-transformed alternating-current voltammetry; mononuclear molybdenum enzyme; protein film electrochemistry; pyranopterin; YedY
Categories
Funding
- University of York
- Royal Society
- Canadian Institutes of Health Research [MOP15292]
- Biotechnology and Biological Sciences Research Council [1359410] Funding Source: researchfish
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A long-standing contradiction in the field of mononuclear Mo enzyme research is that small-molecule chemistry on active-site mimic compounds predicts ligand participation in the electron transfer reactions, but biochemical measurements only suggest metal-centered catalytic electron transfer. With the simultaneous measurement of substrate turnover and reversible electron transfer that is provided by Fourier-transformed alternating-current voltammetry, we show that Escherichia coli YedY is a mononuclear Mo enzyme that reconciles this conflict. In YedY, addition of three protons and three electrons to the well-characterized as-isolated Mo(V) oxidation state is needed to initiate the catalytic reduction of either dimethyl sulfoxide or trimethylamine N-oxide. Based on comparison with earlier studies and our UV-vis redox titration data, we assign the reversible one-proton and one-electron reduction process centered around + 174 mV vs. standard hydrogen electrode at pH 7 to a Mo(V)-to-Mo(IV) conversion but ascribe the two-proton and two-electron transition occurring at negative potential to the organic pyranopterin ligand system. We predict that a dihydro-to-tetrahydro transition is needed to generate the catalytically active state of the enzyme. This is a previously unidentified mechanism, suggested by the structural simplicity of YedY, a protein in which Mo is the only metal site.
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