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 Fe-57-labelled fully reduced Ni-R form of Desulfovibrio vulgaris Miyazaki F [NiFe]-hydrogenase. A unique 'wagging' mode involving H- motion perpendicular to the Ni(mu-H)Fe-57 plane was studied using Fe-57-specific nuclear resonance vibrational spectroscopy and density functional theory (DFT) calculations. On Ni(mu-D)Fe-57 deuteride substitution, this wagging causes a characteristic perturbation of Fe-CO/CN bands. Spectra have been interpreted by comparison with Ni(mu-H/D)Fe-57 enzyme mimics [(dppe)Ni(mu-pdt)(mu-H/D)Fe-57(CO) 3](+) and DFT calculations, which collectively indicate a low-spin Ni(II)(mu-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.