Refinement of the structure of pseudoazurin from Alcaligenes faecalis S-6 at 1.55 A resolution

The crystal structure of the redox protein pseudoazurin (123 amino acid residues; molecular weight 13,000 daltons) from Alcaligenes faecalis has been refined by fast Fourier restrained least-squares minimization. Cycles of rebuilding were carried out to escape from local minima. Individual isotropic temperature factor values were refined separately for all atoms. The R factor was reduced from 0.400 (for 2647 reflections in the 6.0-2.8 A resolution range) to 0.180 (for all 19,770 reflections in the 9.0-1.55 A resolution range) with a final estimated accuracy in atomic positions of 0.15 A. The final model comprises 917 protein atoms and 93 solvent molecules. The root-mean-square shift of the main-chain atoms between the final and the initial model is 0.94 A (maximum shift 1.8 A). Most of the larger shifts were the result of rebuilding on the graphics system. The average atomic temperature factor, B, is 23.0 A2 for all atoms. Side-chain atoms with high B values were omitted, and their positions checked from difference maps. The three carboxy-terminal residues were omitted from the final model as no single conformation could be assigned from the observed electron density. All other protein atoms were included.