title: Differences in substrate and inhibitor kinetics of human type 1 and type 2 3beta-hydroxysteroid dehydrogenase are explained by the type 1 mutant, H156Y.
abstract: Two distinct genes encode the human type 1 (placenta, mammary gland) and type 2 (adrenal, gonad) isoforms of 3beta-hydroxysteroid dehydrogenase/isomerase (3beta-HSD). We have produced the Y154F, H156Y, and K158Q mutant enzymes in the Y154-P-H156-S-K158 motif of the human type 1 3beta-HSD/isomerase. The H156Y mutant was created to produce a chimera of the type 2 enzyme motif (Y154-P-Y156-S-K158) in the type 1 enzyme. The wild-type (WT) 1 and 2 plus the mutant enzymes were expressed and purified. The Km for dehydroepiandrosterone and Ki for epostane measured with both the H156Y mutant and WT 2 are 13-fold to 17-fold greater than those values obtained with the WT 1 3beta-HSD. The Y154F and K158Q mutants exhibit no 3beta-HSD but have significant isomerase activity. Thus, H156 in WT 1 vs. Y156 in WT 2 accounts for the substantially higher affinity of WT 1 3beta-HSD activity for these substrate and inhibitor steroids relative to the WT 2 enzyme.
authors.affiliation: Mercer University School of Medicine, Macon, GA 31207, USA. thomas_j@mercer.edu
authors.forename: James L
authors.initials: JL
authors.lastname: Thomas
authors.forename: J Ian
authors.initials: JI
authors.lastname: Mason
authors.forename: Stacey
authors.initials: S
authors.lastname: Brandt
authors.forename: Wendy
authors.initials: W
authors.lastname: Norris
mesh_terms: D000737:Androstenols / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D003687:Dehydroepiandrosterone / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007313:Insecta; D007527:Isoenzymes / Q000037:antagonists & inhibitors; D007700:Kinetics; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D011375:Progesterone Reductase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D013251:Steroid Isomerases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism
chemical_list: C021425:3 beta-hydroxysteroid oxidoreductase-delta(5) 3-ketosteroid isomerase; D000737:Androstenols; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D009097:Multienzyme Complexes; D003687:Dehydroepiandrosterone; C046855:epostane; D011375:Progesterone Reductase; D013251:Steroid Isomerases