Abstract
Evidence of a CO docking site near the FeMo cofactor in nitrogenase has been obtained by Fourier transform infrared spectroscopy-monitored variable low-temperature photolysis. Evaluation of the Stark splitting of the free 13C18O signal in the pocket revealed an electric field within the pocket comparable to similar work with myoglobin. Subsequently, we investigated the dynamics of the pocket using molecular dynamics. The dynamics revealed a potential substrate gas channel from the active site to the protein exterior. Interestingly, travel through the channel was gated by the motion of protein residues, creating three distinct pockets. By implementing a potential mean force calculation, we have modeled an energy landscape of the channel and gates. These gates may play a role in “loading” nitrogenase with substrate resulting in sequential turnovers that coincide with reduction of the FeMo cofactor. The gated channel investigated here, along with other channels in similar work, hint at a “traffic control” system in nitrogenase that mediates the import of dinitrogen with protons and export of fixed nitrogen with dihydrogen gas.
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