First Crystal Structure for a Gold Carbene–Protein Adduct

The X-ray structure of the adduct formed in the reaction between the gold N-heterocyclic carbene compound Au­(NHC)Cl (with NHC = 1-butyl-3-methyl-imidazole-2-ylidene) and the model protein thaumatin is reported here. The structure reveals binding of Au­(NHC)⁺ fragments to distinct protein sites. Notably, binding of the gold compound occurs at lysine side chains and at the N-terminal tail; the metal binds the protein after releasing Cl^– ligand, but retaining NHC fragment.