Crystallization and preliminary x-ray diffraction studies of a mammalian steroid dehydrogenase

20β-Hydroxysteroid dehydrogenase from the cytosolic fraction of neonatal pig testis is a NADPH-dependent enzyme that catalyzes the reduction of the C-20 ketone of C₂₁-steroids. It is 85% homologous in amino acid sequence to the human enzyme, carbonyl reductase. The enzyme has been crystallized from 36% saturated ammonium sulfate in 10 mM 2-[N-Morpholino]ethanesulfonic acid buffer. The size and the quality of nicely formed square bi-pyramidal crystals were improved by using a "seeding" technique. The crystals diffract X-rays to at least 2.5 Å resolution. The space group is P4₁2₁2 (or P4₃2₁2) and the unit-cell dimensions are a = b = 58.53 A ̊, c = 165.64 A ̊. There is one molecule (M_r = 30.5 kDa; 289 amino acid residues) in the asymmetric unit. An intensity data set to 2.5 Å has been collected with an overall R_merge of 6.6% for all reflections.