Range of substrates and steroid bioconversion reactions performed by recombinant microorganisms Saccharomyces cerevisiae and Yarrowia lipolytica expressing cytochrome P450c17

The relationship between 17α-hydroxylation and 20-oxidation-reduction of progesterone and some of its derivatives was studied in yeast strains Saccharomyces cerevisiae YEp51α, Yarrowia lipolytica E129A15, and expressing cytochrome P450c17. The key metabolites were found to be 17α-hydroxyprogester-one and 17α,20(α,β)-dihydroxypregn-4-ene-3-ones. The bioconversion pathways of pregn-4-ene-20(α,β)-ol-3-ones were determined. They included cycles of 20-oxidation, 17α-hydroxylation, and stereospecific 20-reduction. The efficiency and kinetic parameters of steroid bioconversion by the recombinant strains were determined. The role of yeast analogs of mammalian steroid dehydrogenases is discussed. It was found that any of the desired derivatives, 17α-hydroxyprogesterone or progesterone 17α,20(α,β)-diols, could be obtained from progesterone. Cholesterol bioconversion yields important metabolites: steroid hormones, the vitamin-D group, and bile acids 1, 2]. Attention to various cytochrome-P450 species participating in the biosynthesis of mammalian steroid hormones is caused by two circumstances: (1) the necessity of detecting structural-function abnorm alities of some of the enzymes of steroid-synthesis that cause human diseases, and (2) the potential of regio-and stereospecific cytochrome P450 species of mammals in chemoenzymatic synthesis of pharmacologically valuable steroids. Concerning the second line of inquiry, the development of transgenic Saccharomyces cerevisiae yeast for the complete synthesis of cortisol by additional expression and elimination of a total of 13 genes was reported 3]. To increase the yield of the target compound, the genes for enzymes performing undesirable steroid modifications were inactivated. These modifications included esterification of pregnenolone 4] and 20α-reduction of 17α-hydroxyprogesterone 5]. A search for analogs of mammalian 20α-hydroxysteroid dehydrogenase (20α-HSD) in the Saccharomyces cerevisiae genome revealed two candidate proteins: Ypr1p (yeast aldo-keto reductase) and Gcy1p (yeast galactose-inducible crystallin-like protein) 3]. Indeed, it was formerly shown that expression of cytochrome P450 from bovine adrenal cortex, performing 17α-hydroxylation and the C17,20-lyase reaction (P450c17) in S. cerevisiae under the control of the GAL10-promoter with the presence of D-galactose as an inducer, was accompanied by the sequential conversion of progesterone to 17α-hydroxyprogesterone and 17α,20(α,β)-dihydroxypregn-4-ene-3-one with a high yield 5].