Crystallization and preliminary crystallographic analysis of a flavoprotein NADH oxidase from Lactobacillus brevis.

NADH oxidase (NOX) from Lactobacillus brevis is a homotetrameric flavoenzyme composed of 450 amino acids per subunit. The molecular weight of each monomer is 48.8 kDa. The enzyme catalyzes the oxidation of two equivalents of NADH and reduces one equivalent of oxygen to yield two equivalents of water, without releasing hydrogen peroxide after the reduction of the first equivalent of NADH. Crystals of this protein were grown in the presence of 34% polyethylene glycol monomethyl ether 2000, 0.1 M sodium acetate and 0.2 M ammonium sulfate at pH 5.4. They belong to the tetragonal space group P4(3)2(1)2, with unit-cell parameters a = 74.8, b = 95.7, c = 116.9 A, alpha = gamma = 90, beta = 103.8 degrees. The current diffraction limit is 4.0 A. The self-rotation function of the native data set is consistent with a NOX tetramer in the asymmetric unit.