A novel type of catalytic copper cluster in nitrous oxide reductase

Nitrous oxide (N2O) is a greenhouse gas, the third most significant contrib utor to global warming. As a key process for N2O elimination from the biosp here, N2O reductases catalyze the two-electron reduction of N2O to N-2. The se 2 x 65 kDa copper enzymes are thought to contain a CuA electron entry si te, similar to that of cytochrome c oxidase, and a CuZ catalytic center. Th e copper anomalous signal was used to solve the crystal structure of N2O re ductase from Pseudomonas nautica by multiwavelength anomalous dispersion, t o a resolution of 2.4 Angstrom. The structure reveals that the CuZ center b elongs to a new type of metal cluster, in which four copper ions are ligand ed by seven histidine residues. N2O binds to this center via a single coppe r ion. The remaining copper ions might act as an electron reservoir, assuri ng a fast electron transfer and avoiding the formation of dead-end products .