Nitrogenase is the only known enzyme that can reduce dinitrogen to ammonia. The catalytic MoFe-Protein of nitrogenase contains two unique superclusters: FeMoco, which is the site of catalysis and is extensively studied, and the P-cluster, which is the intermediary electron relay site. Reduction of dinitrogen requires the coordinated transfer of many electrons and protons to FeMoco, a process mediated by the P-cluster. There is growing evidence that the P-cluster behaves as an active gate-keeper in the transfer of electrons to FeMoco. Understanding the P-cluster’s dynamic role as an electron conduit in dinitrogen reduction is vital to elucidating the catalytic mechanism of nitrogenase. We hypothesize that mechano-redox coupling opens a conformational gate which makes electron transfer from the P-cluster to FeMoco a favorable process. Such a gate would require the primary coordination sphere of the P-cluster to be fluxional. Gating has been supported by our previous studies that discovered the conservation of a hard, oxygen-based ligand (Ser or Tyr) that ligates the 2-electron oxidized P-cluster. Recently, I constructed <i>Azotobacter vinelandii</i> MoFe-Protein mutants in which the primary coordination sphere ligands of the P-cluster have been altered. Characterization of these mutants with EPR and X-ray crystallography demonstrates that the P-cluster is an intrinsically labile iron-sulfur cluster in which the primary coordination sphere ligands dictate the accessible oxidation states and maintain the cluster on the brink of stability.

On the brink of lability: Stabilization of the nitrogenase P-cluster by a redox-switchable ligand

2019 Fall National Meeting

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