Carbene in Cupredoxin Protein Scaffolds: Replacement of a Histidine Ligand in the Active Site Substantially Alters Copper Redox Properties

Abstract

AbstractN‐heterocyclic carbene (NHC) ligands have had a major impact in homogeneous catalysis, however, their potential role in biological systems is essentially unexplored. We replaced a copper‐coordinating histidine (His) in the active site of the redox enzyme azurin with exogenous dimethyl imidazolylidene. This NHC rapidly restores the type‐1 Cu center, with spectroscopic properties (EPR, UV/Vis) that are identical to those from N‐coordination of the His in the wild type. However, the introduction of the NHC markedly alters the redox potential of the metal, which is a key functionality of this blue copper protein. These results suggest that C‐bonding for histidine is plausible and a potentially relevant bonding mode of redox‐active metalloenzymes in their (transient) active states.