MOLECULAR-CLONING OF A NOVEL WIDELY EXPRESSED HUMAN 80 KDA 17-BETA-HYDROXYSTEROID DEHYDROGENASE-IV

Reactions of oestrogens and androgens at position C-17 are catalysed b y 17 beta-hydroxysteroid dehydrogenases (17 beta-HSDs). Cloning of the cDNA of a novel human 17 beta-HSD IV and expression of its mRNA are d escribed. A probe derived from the recently discovered porcine 17 beta -oestradiol dehydrogenase (17 beta-EDH) was used to isolate a 2.6 kb h uman cDNA encoding a continuous protein of 736 amino acids of high (84 %) similarity to the porcine 17 beta-EDH. The calculated molecular ma ss of the human enzyme is 79 595 Da. Other sequence similarities share d by the two enzymes are: an N-terminal sequence which is similar to t hat of members of the short-chain alcohol dehydrogenase family; amino acids 343-607 which are similar to the C-terminal domains of a trifunc tional Candida tropicalis enzyme and the FOX2 gene product of Saccharo myces cerevisiae; amino acids 596-736 which are similar to human stero l carrier protein 2. The previously cloned human 17 beta-HSD I, II and III are less than 25% identical with 17 beta-HSD IV. mRNA for HSD IV is a single species of 3.0 kb, present in many tissues with highest co ncentrations in liver, heart, prostate and testes. When overexpressed in mammalian cells, the human 17 beta-HSD IV enzyme displays a specifi c unidirectional oxidative 17 beta-HSD activity.