Crystallization of the Na+-translocating NADH:quinone oxidoreductase from Vibrio cholerae

The Na+-translocating NADH:quinone oxidoreductase (Na+-NQR) from the human pathogen Vibrio cholerae couples the exergonic oxidation of NADH by membrane-bound quinone to Na+ translocation across the membrane. Na+-NQR consists of six different subunits (NqrA-NqrF) and contains a [2Fe-2S] cluster, a noncovalently bound FAD, a noncovalently bound riboflavin, two covalently bound FMNs and potentially Q(8) as cofactors. Initial crystallization of the entire Na+-NQR complex was achieved by the sitting-drop method using a nanolitre dispenser. Optimization of the crystallization conditions yielded flat yellow-coloured crystals with dimensions of up to 200 x 80 x 20 mu m. The crystals diffracted to 4.0 A resolution and belonged to space group P2(1), with unit-cell parameters a = 94, b = 146, c = 105 A, alpha = gamma = 90, beta = 111 degrees.