Revisiting the catalytic CuZ cluster of nitrous oxide (N2O) reductase -: Evidence of a bridging inorganic sulfur

Nitrous-oxide reductases (N2OR) catalyze the two-electron reduction of N2O to N-2. The crystal structure of N(2)ORs from Pseudomonas nautica (Pn) and Paracoccus denitrificans (Pd) were solved at resolutions of 2.4 and 1.6 Angstrom respectively. The Pn N2OR structure revealed that the catalytic CuZ center belongs to a new type of metal cluster in which four copper ions are liganded by seven histidine residues. A bridging oxygen moiety and two other hydroxide ligands were proposed to complete the ligation scheme (Brown, K., Tegoni, RI., Prudencio, M., Pereira, A. S., Besson, S., Moura, J. J. G., Moura, I., and Cambillau, C, (2000) Nat. Struct Biol. 7, 191-195). However, in the CuZ cluster, inorganic sulfur chemical determination and the high resolution structure of Pd N2OR identified a bridging inorganic sulfur instead of an oxygen, This result reconciles the novel CuZ cluster with the hitherto puzzling spectroscopic data.