Incorporation of an Asymmetric Mo-Fe-S Cluster as an Artificial Cofactor into Nitrogenase

Nitrogenase employs a sophisticated electron transfer system and a Mo-Fe-S-C cofactor, designated the M-cluster [(cit)MoFe7S9C]), to reduce atmospheric N-2 to bioaccessible NH3. Previously, we have shown that the cofactor-free form of nitrogenase can be repurposed as a protein scaffold for the incorporation of a synthetic Fe-S cluster [Fe6S9(SEt)(2)](4-). Here, we demonstrate the utility of an asymmetric Mo-Fe-S cluster [Cp*MoFe5S9(SH)](3-) as an alternative artificial cofactor upon incorporation into the cofactor-free nitrogenase scaffold. The resultant semi-artificial enzyme catalytically reduces C2H2 to C2H4, and CN- into short-chain hydrocarbons, yet it is clearly distinct in activity from its [Fe6S9(SEt)(2)](4-)-reconstituted counterpart, pointing to the possibility to employ molecular design and cluster synthesis strategies to further develop semi-artificial or artificial systems with desired catalytic activities.