Crystallization and preliminary crystallographic analysis of the hydroxyquinol 1,2-dioxygenase from Nocardioides simplex 3E: a novel dioxygenase involved in the biodegradation of polychlorinated aromatic compounds

Hydroxyquinol 1,2-dioxygenase (HQ1,2O) from Nocardioides simplex 3E, an enz yme involved in the aerobic biodegradation of a large class of chloroaromat ic compounds such as 2,4-dichlorophenoxyacetate (2,4-D) and 2,4,5-trichloro phenoxyacetate (2,4,5-T), has been crystallized. HQ1,2O, which specifically catalyzes the intradiol cleavage of hydroxyquinol (1,2,4-trihydroxybenzene ), an intermediate in the degradation of a variety of aromatic pollutants, to maleylacetate, has been recently purified to homogeneity. The enzyme is an homodimer composed of two identical subunits in a alpha(2)-type quaterna ry structure, has a molecular weight of about 65 kDa and contains a catalyt ically essential Fe(III) ion. Crystals of HQ1,2O obtained using 2% PEG 400 and 2 M ammonium sulfate at pH 7.5 as precipitants belong to the orthorhomb ic space group P2(1)2(1)2(1), with unit-cell parameters a = 81.15(6), b = 8 6.79(7), c = 114.93(8). Assuming one dimer per asymmetric unit, the V-m val ue is 2.51 Angstrom(3) Da(-1). A complete native data set to 1.8 Angstrom r esolution has been collected on a laboratory source. This is the first intr adiol dioxygenase which specifically catalyzes the cleavage of hydroxyquino l to give diffraction-quality crystals.