A Novel Type of Catalytic Copper Cluster in Nitrous Oxide Reductase

Abstract

Nitrous oxide (N2O) is a greenhouse gas, the third most significant contributor to global warming. As a key process for N2O elimination from the biosphere, N2O reductases catalyze the two-electron reduction of N2O to N2. These 2 × 65 kDa copper enzymes are thought to contain a CuA electron entry site, similar to that of cytochrome c oxidase, and a CuZ catalytic center. The copper anomalous signal was used to solve the crystal structure of N2O reductase from Pseudomonas nautica by multiwavelength anomalous dispersion, to a resolution of 2.4 A. The structure reveals that the CuZ center belongs to a new type of metal cluster, in which four copper ions are liganded by seven histidine residues. N2O binds to this center via a single copper ion. The remaining copper ions might act as an electron reservoir, assuring a fast electron transfer and avoiding the formation of dead-end products.