Wüst A, Schneider L, Pomowski A, Zumft WG, Kroneck PMH, Einsle O (2012)

Nature's way of handling a greenhouse gas: the copper-sulfur cluster of purple nitrous oxide reductase.

Biol. Chem. 393: 1067-1077 (2012).

The tetranuclear Cu_Z cluster is the unique active site of nitrous oxide reductase, the enzyme that catalyses the reduction of nitrous oxide to dinitrogen as the final reaction in bacterial denitrification. Three-dimensional structures of orthologs of the enzyme from a variety of different bacterial species were essential steps in the elucidation of the properties of this centre. However, while structural data first revealed and later confirmed the presence of four copper ions in spectroscopically distinct forms of Cu_Z, the exact structure and stoichiometry of the cluster showed significant variations. A ligand, bridging ions Cu_Z1 and Cu_Z2, was initially assigned as a water or hydroxo species in the structures from Pseudomonas nautica (now Marinobacter hydrocarbonoclasticus) and Paracoccus denitrificans. This ligand was absent in a structure from “Achromobacter cycloclastes”, and could be reconstituted by iodide that acted as an inhibitor of catalysis. A recent structure of anoxically isolated N₂O reductase from Pseudomonas stutzeri revealed the bridging ligand to be sulfide, S^2–, and showed an unprecedented side-on mode of nitrous oxide binding to this form of Cu_Z.