Blue to type 2 binding. Copper(II) and cobalt(II) derivatives of a Cys112Asp mutant of Pseudomonas aeruginosa azurin

Of the five invariant residues that surround the copper in azurins, the ligand cysteine at position 112 (Cys112) is believed to be especially important in the bonding interactions responsible for the unusual blue copper absorption and electron paramagnetic resonance (EPR) spectra. It is striking that mutagenesis studies of Met121, His46, and His174 ave shown that these ligands are not required for a blue copper center, thereby reinforcing the feeling that Cys112 is absolutely essential. To address this issue directly, we have replaced Cys112 with Asp by site-directed mutagenesis.