CRYSTALLIZATION AND PRELIMINARY-X-RAY DIFFRACTION STUDIES OF A MAMMALIAN STEROID DEHYDROGENASE

20Beta-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 angstrom resolution. The space group is P4(3)2(1)2 (or P4(3)2(1)2) and the unit-cell dimensions are a = b = 58.53 angstrom, c = 165.64 angstrom. There is one molecule (M(r) = 30.5 kDa; 289 amino acid residues) in the asymmetric unit. An intensity data set to 2.5 angstrom has been collected with an overall R(merge) of 6.6% for all reflections.