X-RAY CRYSTAL-STRUCTURE OF THE 2 SITE-SPECIFIC MUTANTS ILE7SER AND PHE 110SER OF AZURIN FROM PSEUDOMONAS-AERUGINOSA

The blue copper protein azurin from Pseudomonas aeruginosa contains a single Trp residue that is believed to be involved in the inducible in tramolecular electron transfer from a disulphide group to the copper c entre. This residue shows in fluorescence spectra the highest energy e mission of tryptophan-containing compounds at room temperature, which is explained by its rigid and highly hydrophobic environment. In order to investigate the role of the Trp residue in electron transfer and t he influence of its environment, two mutations (I7S and F11OS) were in troduced that were thought to increase the polarity and the mobility i n its environment. The crystal structures of these mutants were solved at 2.2 Angstrom and 2.3 Angstrom resolution, respectively These provi de a structural basis for the changes observed in fluorescence spectra compared with the wild-type protein. We conclude from our results tha t these changes are not caused by a change in the dynamics of the Trp residue itself, but exclusively by an increased effective dielectric c onstant of the microenvironment of Trp48 and by changes in mobility of the mutated residues. (C) 1996 Academic Press Limited