STRUCTURE OF THE AZURIN MUTANT PHE114ALA FROM PSEUDOMONAS-AERUGINOSA AT 2.6-ANGSTROM RESOLUTION

The crystal structure of azurin mutant Phe114Ala from Pseudomonas aeru ginosa has been solved by molecular replacement. The final crystallogr aphic R value is 0.185 for 9832 reflections to a resolution of 2.6 Ang strom. The root-mean-square deviation for main-chain atom positions is 0.020 Angstrom between the four independent monomers in the asymmetri c unit. The mutant Ala114 crystallized from PEG 4000 in a new crystal form and the crystals are monoclinic, P2(1), a = 51.0, b = 83.6, c = 6 6.4 Angstrom and beta = 110.5 degrees. The four molecules in the asymm etric unit are packed as a dimer of dimers and are related by an appro ximate twofold axis. The dimer packing and the dimer contact region ar e very similar to that of the Alcaligenes denitrificans azurin dimer. The mutation was performed at residue Phe114, which exhibits a pi-elec tron overlap with the copper ligand His117, to investigate its suggest ed role in the electron self-exchange reaction. Removal of steric cons trains from the phenylalanine side chain created a somewhat different geometry around the copper site with an increased mobility of His117 r esulting in an enlarged Cu-N length which may be responsible for the s light differences obtained in the spectral properties of the mutant ve rsus the wild-type protein.