Crystallization and preliminary X-ray analysis of nitrous oxide reductase from Paracoccus pantotrophus.

Nitrous oxide reductase is a periplasmic respiratory protein with a novel copper catalytic centre; it catalyses the terminal step, reduction of nitrous oxide to nitrogen, of the bacterial denitrification process. Nitrous oxide reductase from Paracoccus pantotrophus has been crystallized by the hanging-drop method. A prerequisite for crystallization was the oxidation of the enzyme with potassium ferricyanide in order to obtain homogenous oxidation states of the copper centres. The crystals belong to space group P2(1)2(1)2(1), with unit-cell parameters a = 116.4, b = 118.3, c = 267.0 A. Two homodimers, of approximate molecular weight 67 kDa per subunit, probably constitute the asymmetric unit and give a Matthews coefficient, V(m), of 3.4 A(3) Da(-1) and a solvent content of 59% by volume. The crystals diffract X-rays to 3.0 A resolution on an in-house source and are suitable for structure determination.