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The enzyme 3beta/17beta-hydroxysteroid dehydrogenase (3beta/17beta-HSD) is a steroid-inducible component of the Gram-negative bacterium Comamonas testosteroni. It catalyzes the reversible reduction/dehydrogenation of the oxo/beta-hydroxy groups at positions 3 and 17 of steroid compounds, including hormones and isobile acids. Crystallographic analysis at 1.2 A resolution reveals the enzyme to have nearly identical subunits that form a tetramer with 222 symmetry. This is one of the largest oligomeric structures refined at this resolution. The subunit consists of a monomer with a single-domain structure built around a seven-stranded beta-sheet flanked by six alpha-helices. The active site contains a Ser-Tyr-Lys triad, typical for short-chain dehydrogenases/reductases (SDR). Despite their highly diverse substrate specificities, SDR members show a close to identical folding pattern architectures and a common catalytic mechanism. In contrast to other SDR apostructures determined, the substrate binding loop is well-defined. Analysis of structure-activity relationships of catalytic cleft residues, docking analysis of substrates and inhibitors, and accessible surface analysis explains how 3beta/17beta-HSD accommodates steroid substrates of different conformations.

Type

Journal article

Journal

Biochemistry

Publication Date

17/12/2002

Volume

41

Pages

14659 - 14668

Keywords

17-Hydroxysteroid Dehydrogenases, Androgens, Apoenzymes, Bacterial Proteins, Bile Acids and Salts, Binding Sites, Comamonas testosteroni, Crystallography, X-Ray, Estrogens, Models, Molecular, Point Mutation, Protein Folding, Protein Structure, Tertiary, Stereoisomerism, Substrate Specificity