Mutations of the Weak Axial Ligand in the Thermus CuA Center Modulates Its Electronic Structure

Here we report the first stable, axial ligand mutations, 160Gln and Met160Glu, of a Cu_A center in the Thermus (TtIICu_A) fragment of cytochrome ba3.2a The , delocalized (S = 1/2) Cu_A center serves as the initial electron acceptor in cytochrome c oxidases (COX) and nitrous oxide reductase (N_2OR). The Cu_A domains and the type 1 (T1) blue copper centers are members of the cupredoxin superfamily of electron transfer (ET) proteins. The Cu_A centers have two bridging Cys thiolates, two terminal His imidazole ligands, and one weak axial ligand to each copper, a Met thioether or the peptide carbonyl of Glu (Figure 1). The weak axial ligands give each Cu a distorted tetrahedral geometry, similar to the T1 .