Crystallization and preliminary analysis of a water-forming NADH oxidase from Lactobacillus sanfranciscensis

Single crystals have been obtained of NADH oxidase (Nox), a flavoenzyme cloned from Lactobacillus sanfranciscensis. The enzyme catalyzes the oxidation of two equivalents of NAD(P)H and reduces one equivalent of oxygen to yield two equivalents of water, without releasing hydrogen peroxide after the reduction of the first equivalent of NAD(P)H. The enzyme crystallizes in space group P2(1)2(1)2(1), with unit-cell parameters a = 59.6, b = 92.6, c = 163.5 A. The crystals diffract to 1.85 A resolution using synchrotron radiation. Matthews coefficient calculations suggest the presence of two molecules per asymmetric unit (V(M) = 2.3 A(3) Da(-1), 45.5% solvent content), which has been confirmed by the molecular-replacement solution using a search molecule derived from NADH peroxidase (PDB code 1f8w).