Mapping of the binding site on pseudoazurin in the transient 152 kDa complex with nitrite reductase.

Nitrite reductase (NiR) catalyzes the reduction of nitrite to nitrite oxide as a part of the denitrification process. In Alcaligenes faecalis S-6, the copper protein pseudoazurin acts as electron donor to NiR. The binding surface of pseudoazurin involved in the formation of the 152 kDa complex with NiR has been determined by NMR using cross saturation from NiR to perdeuterated pseudoazurin. Due to the transient nature of the complex, saturation effects can be observed on the resonances of the unbound protein. The binding site comprises the hydrophobic area surrounding the exposed copper ligand His81, suggesting that this residue is important for efficient electron transfer.