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(μ1/4-H)⁵⁷ Fe plane was studied using ⁵⁷ Fe-specific nuclear resonance vibrational spectroscopy and density functional theory (DFT) calculations. On Ni(μ1/4-D) ⁵⁷ Fe deuteride substitution, this wagging causes a characteristic perturbation of Fe-CO/CN bands. Spectra have been interpreted by comparison with Ni(μ1/4-H/D) ⁵⁷ Fe enzyme mimics [(dppe)Ni(μ1/4-pdt)(μ1/4-H/D) ⁵⁷ Fe(CO)₃ ]⁺ and DFT calculations, which collectively indicate a low-spin Ni(II)(μ1/4-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.