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

Abstract

The tetranuclear CuZ cluster is the unique active site of nitrous oxide reductase, the enzyme that catalyzes the reduction of nitrous oxide to dinitrogen as the fi nal reaction in bacterial denitrifi cation. 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 center. However, while structural data first revealed and later confirmed the presence of four copper ions in spectroscopically distinct forms of CuZ, the exact structure and stoichiometry of the cluster showed signifi cant variations. A ligand bridging ions CuZ1 and CuZ2 was initially assigned as a water or hydroxo species in the structures from Pseudomonas nautica (now Marinobacter hydrocarbonoclasticus) and Paracoccus denitrifi cans. 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 nitrous oxide reductase from Pseudomonas stutzeri revealed the bridging ligand to be sulfi de, S2-, and showed an unprecedented side-on mode of nitrous oxide binding to this form of CuZ. Copyright © 2011-2012 by Walter de Gruyter.