Crystallization and preliminary X-ray diffraction analysis of a complex between the electron-transfer partners hexameric Cu-containing nitrite reductase and pseudoazurin.

The complex between Cu-containing nitrite reductase (HdNIR) and its electron-donor protein pseudoazurin (HdPAz) from Hyphomicrobium denitrificans has been crystallized. The crystals were obtained from a mixture of the two proteins using the hanging-drop vapour-diffusion method in the presence of polyethylene glycol (PEG) and 2-methyl-2,4-pentanediol (MPD) as precipitants. SDS-PAGE analysis demonstrated that the crystals contained both proteins. The X-ray diffraction experiment was carried out at SPring-8 and diffraction data were collected to 3.3 A resolution. The crystals were tetragonal (space group P4(1)2(1)2), with unit-cell parameters a = b = 130.39, c = 505.55 A. Preliminary analysis indicated that there was one HdNIR and at least two HdPAz molecules in the asymmetric unit of the crystal.