Crystallographic study of dioxygen chemistry in a copper-containing nitrite reductase from Geobacillus thermodenitrificans.

Copper-containing nitrite reductases (CuNIRs) are multifunctional enzymes that catalyse the one-electron reduction of nitrite (NO) to nitric oxide (NO) and the two-electron reduction of dioxygen (O) to hydrogen peroxide (HO). In contrast to the mechanism of nitrite reduction, that of dioxygen reduction is poorly understood. Here, results from anaerobic synchrotron-radiation crystallography (SRX) and aerobic in-house radiation crystallography (iHRX) with a CuNIR from the thermophile Geobacillus thermodenitrificans (GtNIR) support the hypothesis that the dioxygen present in an aerobically manipulated crystal can bind to the catalytic type 2 copper (T2Cu) site of GtNIR during SRX experiments.