Crystallization of purple nitrous oxide reductase from Pseudomonas stutzeri

Nitrous oxide reductase (N₂OR) from Pseudomonas stutzeri catalyzes the final step in denitrification: the two-electron reduction of nitrous oxide to molecular dinitrogen. Crystals of the enzyme were grown under strict exclusion of dioxygen by sitting-drop vapour diffusion using 2R,3R-butanediol as a cryoprotectant. N₂OR crystallized in either space group P1 or P6₅. Interestingly, the key determinant for the resulting space group was the crystallization temperature. Crystals belonging to space group P1 contained four 130 kDa dimers in the asymmetric unit, while crystals belonging to space group P6₅ contained a single dimer in the asymmetric unit. Diffraction data were collected to resolutions better than 2 Å.