The catalytic roles of P185 and T188 and substrate-binding loop flexibility in 3α-hydroxysteroid dehydrogenase/carbonyl reductase from Comamonas testosteroni.

ABSTRACT: 3α-Hydroxysteroid dehydrogenase/carbonyl reductase from Comamonas testosteroni reversibly catalyzes the oxidation of androsterone with NAD(+) to form androstanedione and NADH. Structurally the substrate-binding loop of the residues, T188-K208, is unresolved, while binding with NAD(+) causes the appearance of T188-P191 in the binary complex. This study determines the functional roles of the flexible substrate-binding loop in conformational changes and enzyme catalysis. A stopped-flow study reveals that the rate-limiting step in the reaction is the release of the NADH. The mutation at P185 in the hinge region and T188 in the loop causes a significant increase in the Kd value for NADH by fluorescence titration. A kinetic study of the mutants of P185A, P185G, T188A and T188S shows an increase

SUBMITTER: Hwang CC 

PROVIDER: S-EPMC3662788 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature