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Anion Binding and Oxidative Modification at the Molybdenum Cofactor of Formate Dehydrogenase from Rhodobacter capsulatus Studied by X‑ray Absorption Spectroscopy
journal contribution
posted on 2019-12-08, 20:03 authored by Benjamin
R. Duffus, Peer Schrapers, Nils Schuth, Stefan Mebs, Holger Dau, Silke Leimkühler, Michael HaumannFormate dehydrogenase (FDH) enzymes are versatile catalysts
for
CO2 conversion. The FDH from Rhodobacter capsulatus contains a molybdenum cofactor with the dithiolene functions of
two pyranopterin guanine dinucleotide molecules, a conserved cysteine,
and a sulfido group bound at Mo(VI). In this study, we focused on
metal oxidation state and coordination changes in response to exposure
to O2, inhibitory anions, and redox agents using X-ray
absorption spectroscopy (XAS) at the Mo K-edge. Differences in the
oxidative modification of the bis-molybdopterin guanine dinucleotide
(bis-MGD) cofactor relative to samples prepared aerobically without
inhibitor, such as variations in the relative numbers of sulfido (MoS)
and oxo (MoO) bonds, were observed in the presence of azide
(N3–) or cyanate (OCN–). Azide provided best protection against O2, resulting
in a quantitatively sulfurated cofactor with a displaced cysteine
ligand and optimized formate oxidation activity. Replacement of the
cysteine ligand by a formate (HCO2–)
ligand at the molybdenum in active enzyme is compatible with our XAS
data. Cyanide (CN–) inactivated the enzyme by replacing
the sulfido ligand at Mo(VI) with an oxo ligand. Evidence that the
sulfido group may become protonated upon molybdenum reduction was
obtained. Our results emphasize the role of coordination flexibility
at the molybdenum center during inhibitory and catalytic processes
of FDH enzymes.
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coordinationcysteine ligandenzymeXASmolybdenumoxoOCNRhodobacter capsulatus StudiedcofactorMobis-molybdopterin guanine dinucleotideHCOoptimized formate oxidation activitysulfido groupFDHCO 2 conversionFormateCNO 2metal oxidation stateX-ray absorption spectroscopypyranopterin guanine dinucleotide molecules
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