Crystals of active tetramers of 3α,20β-hydroxysteroid dehydrogenase

The NADH-dependent steroid metabolizing enzyme 3α,20β-hydroxysteroid dehydrogenase (EC 1.1.1.53), from Streptomyces hydrogenans, has been crystallized in the active tetrameric form. Single crystals (~0.75 x 0.40 x 0.40 mm) of square bipyramid shape have been grown reproducibly at room temperature in the presence of excess NADH. Diffraction experiments have been performed at the Cornell High Energy Synchrotron Source. The space group is P4₃2₁2 or its enantiomorph, and the cell dimensions are a = 106.0(5) Å and c = 204(1) Å. The asymmetric unit is a tetramer of identical subunits of approximately 25,000 daltons each. The specific volume is 2.8 ų/dalton. A native data set at 2.5-Å resolution has been collected. Two potential heavy atom derivatives, with K₂Pt(CN)₄ and KAu(CN)₂, have been identified from the diffraction photographs.