Hydride bridge in [NiFe]-hydrogenase observed by nuclear resonance vibrational spectroscopy

The metabolism of many anaerobes relies on [NiFe]-hydrogenases, whose characterization when bound to substrates has proven non-trivial. Presented here is direct evidence for a hydride bridge in the active site of the 57 Fe-labelled fully reduced Ni-R form of Desulfovibrio vulgaris Miyazaki F [NiFe]-hydrogenase. A unique ‘wagging’ mode involving H − motion perpendicular to the Ni( μ -H) 57 Fe plane was studied using 57 Fe-specific nuclear resonance vibrational spectroscopy and density functional theory (DFT) calculations. On Ni( μ -D) 57 Fe deuteride substitution, this wagging causes a characteristic perturbation of Fe–CO/CN bands. Spectra have been interpreted by comparison with Ni( μ -H/D) 57 Fe enzyme mimics [(dppe)Ni( μ -pdt)( μ -H/D) 57 Fe(CO) 3 ] + and DFT calculations, which collectively indicate a low-spin Ni( II )( μ -H)Fe( II ) core for Ni-R, with H − binding Ni more tightly than Fe. The present methodology is also relevant to characterizing Fe–H moieties in other important natural and synthetic catalysts.