STRUCTURE OF AZURIN-I FROM THE DENITRIFYING BACTERIUM ALCALIGENES XYLOSOXIDANS NCIMB-11015 AT 2.45 ANGSTROM RESOLUTION

Azurin I from Alcaligenes xylosoxidans NCIMB 11015 (AzN-I) was crystal lized by using PEG 4000 as a precipitant. The crystals belong to the m onoclinic crystal system and have a space group C2 with the unit-cell parameters of a 130.67, b = 54.26, c = 74.55 Angstrom, and beta = 95.9 9 degrees. The structure of AzN-I has been solved by the molecular rep lacement method. Azurin LT from the same bacterium (AzN-II) was chosen as the initial structural model. The final crystallographic R value i s 17.3% and free R value is 23.6% for 10 958 reflections at a resoluti on of 2.45 Angstrom. The root-mean-square deviations for main-chain at oms range between 0.19 and 0.26 Angstrom among the four independent mo lecules in the asymmetric unit. The Cu atom is coordinated to N delta of His46 and His117 at 2.0 (1) and 1.9 (1) Angstrom, and to S gamma of Cys112 at 2.2 (1) Angstrom, while the carbonyl O atom of Gly45 and S delta of Met121 coordinate axially to Cu atom at 2.5 (1) and 3.1 (1) A ngstrom, respectively. The Cu-N and Cu-S distances of AzN-I are quite similar to those of AzN-II, however, the Cu-O (Gly45) bond length in A zN-I is 0.25 Angstrom shorter than its counterpart in AzN-II. The resu lts have been used to discuss the differences in the spectra of these two proteins.