X-ray Structure of the Cupredoxin Amicyanin, from Paracoccus denitrificans, Refined at 1.31 Å Resolution

High-resolution X-ray diffraction data to d_min = 1.31 Å were collected on a Xuong-Hamlin area detector from crystals of the blue-copper protein amicyanin, isolated from P. denitrificans. With coordinates from the earlier 2.0 Å structure determination as a starting point, simulated annealing and restrained positional and temperature factor refinements using the program X-PLOR resulted in a final R factor of 15.5%, based on 21 131 unique reflections in the range 8.0-1.3 Å. Comparison of the 1.31 Å structure with that at 2.0 Å shows the same basic features. However, the high-resolution electron-density maps clearly reveal additional solvent molecules and significant discrete disorder in protein side chains and within the solvent structure. As a consequence of modelling side-chain disorder, several new hydrogen-bonding interactions were identified.