Structural Basis of Biological N2O Generation by Bacterial Nitric Oxide Reductase

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Science  25 Nov 2010:
DOI: 10.1126/science.1195591


Nitric oxide reductase (NOR) is an iron-containing enzyme that catalyzes the reduction of nitric oxide (NO) to generate a major greenhouse gas nitrous oxide (N2O). Here, we report the crystal structure of NOR from Pseudomonas aeruginosa at 2.7 Å resolution. The structure reveals details of the catalytic binuclear center. The non-heme iron (FeB) is coordinated by three His and one Glu ligands, but a His-Tyr covalent linkage common in cytochrome oxidases (COX) is absent. This structural characteristic is crucial for NOR reaction. Although the overall structure of NOR is closely related to COX, neither the D- nor K- proton pathway, connecting the COX active center to the intracellular space, was observed. Protons required for the NOR reaction are likely provided from the extracellular side.