Electrochemical evidence that pyranopterin redox chemistry controls the catalysis of YedY, a mononuclear Mo enzyme
Hope Adamson a, Alexandr N. Simonov b, Michelina Kierzek c, Richard A. Rothery c, Joel H. Weiner c, Alan M. Bond b, and Alison Parkin a,1
a Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom;
b School of Chemistry, Monash University, Clayton, VIC 3800, Australia; and
c Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
Edited by Harry B. Gray, California Institute of Technology, Pasadena, CA, and approved October 13, 2015 (received for review August 25, 2015)
http://www.pnas.org/content/112/47/14506.short
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 oneproton
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.
a Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom;
b School of Chemistry, Monash University, Clayton, VIC 3800, Australia; and
c Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
Edited by Harry B. Gray, California Institute of Technology, Pasadena, CA, and approved October 13, 2015 (received for review August 25, 2015)
http://www.pnas.org/content/112/47/14506.short
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 oneproton
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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