Structure/function relationships responsible for coenzyme specificity and the isomerase activity of XXXX type 1 3 beta-hydroxysteroid dehydrogenase/isomerase.

@entity1 @entity2125 @entity1522 @entity1472 @entity263 @entity0 @entity1420 @entity72294 @entity3333 @entity2494 @entity858 @entity72297 @entity72298 @entity1110 @entity72296 @entity3649 @entity72295 @entity2574 @entity2671 @entity64953
@entity1 type 1 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD/isomerase) catalyzes the two sequential enzyme reactions on a single protein that converts @entity2494 or @entity3333 to @entity2671 or @entity1420 , respectively, in placenta, mammary gland, @entity0 , prostate, @entity263 , and other peripheral tissues. Our earlier studies show that the two enzyme reactions are linked by the coenzyme product, @entity2125 , of the 3 beta-HSD activity. @entity2125 activates the isomerase activity by inducing a time-dependent conformational change in the enzyme protein. The current study tested the hypothesis that the 3 beta-HSD and isomerase activities shared a common coenzyme domain, and it characterized key @entity1522 that participated in coenzyme binding and the isomerase reaction. Homology modeling with @entity858 - @entity3649 -4-epimerase predicts that Asp36 is responsible for the NAD(H) specificity of @entity1 3 beta-HSD/isomerase and identifies the Rossmann-fold coenzyme domain at the @entity1472 terminus. The @entity72294 / @entity72295 mutant in the potential coenzyme domain and the @entity64953 , @entity72296 , @entity72297 , and @entity72298 mutants in the potential isomerase domain (previously identified by affinity labeling) were created, expressed, and purified. The @entity72294 / @entity72295 mutant shifts the cofactor preference of both 3 beta-HSD and isomerase from @entity2125 (H) to @entity1110 (H), which shows that the two activities utilize a common coenzyme domain. The @entity72296 and @entity72297 mutations eliminate isomerase activity, whereas the @entity64953 and @entity72298 mutants have nearly full isomerase activity. Kinetic analyses and pH dependence studies showed that either @entity2574 257 or @entity2574 258 plays a catalytic role in the isomerization reaction. These observations further characterize the structure/function relationships of @entity1 3 beta-HSD/isomerase and bring us closer to the goal of selectively inhibiting the type 1 enzyme in placenta (to control the timing of labor) or in hormone-sensitive @entity0 (to slow their growth).
