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 Å resolution. The crystals were tetragonal (space group P4₁2₁2), with unit‐cell parameters a = b = 130.39, c = 505.55 Å. Preliminary analysis indicated that there was one HdNIR and at least two HdPAz molecules in the asymmetric unit of the crystal.