Electronic Spectroscopy of Gold(I) Pseudomonasaeruginosa Azurin Derivatives

The trigonal (His_2Cys) coordination of blue copper sites in proteins favors Cu(I) over Cu(II), as reflected in the relatively high Cu^(II/I) reduction potentials; and the rigid polypeptide environment minimizes Cu^(II/I) nuclear reorganization, thereby facilitating long-range electron-transfer reactions with donor and acceptor molecules. Although blue Cu(II) sites exhibit rich spectroscopic and magnetic properties, the corresponding Cu(I) proteins do not; indeed, the methods that can be employed to investigate d^(10) metal sites are very limited. Because recent work has shown that Au(I) has geometry-sensitive d-p absorptions and emissions, we are using this 5d^(10) ion to probe ligand interactions in the Cu(I) sites of proteins. Here we report the electronic spectroscopy of Au(I)-substituted wild-type (WT) Pseudomonas aeruginosa azurin as well as the Au(I) derivative of a mutant in which the methionine at position 121 has been replaced with glycine (Met121Gly).