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Mitochondrial cytochrome P450 enzymes play a crucial role in the steroid biosynthesis in human adrenals, catalyzing regio- and stereospecific hydroxylations. In search of a new model system for the study of these enzymes, we expressed the human CYP11B2 (aldosterone synthase, P450(aldo)) in fission yeast Schizosaccharomyces pombe. Analysis of the subcellular localization of the P450 enzyme by Western blot analysis, fluorescence microscopy, and electron microscopy demonstrated that the mitochondrial localization signal of the human protein is functional in S. pombe. The transformed yeasts show the inducible ability to convert in vivo considerable amounts of 11-deoxycortisol to cortisol and 11-deoxycorticosterone to corticosterone, 18-hydroxycorticosterone, and aldosterone, respectively. Although in mammalian cells, mitochondrial steroid hydroxylases depend for their activity on an electron transport chain that consists of two proteins, adrenodoxin and adrenodoxin reductase, no coexpression of these proteins is needed for efficient substrate conversion by intact fission yeast cells. Searching the fission yeast genome for adrenodoxin homologues, a gene was identified that codes for a protein with an amino terminal domain homologous to COX15 of Saccharomyces cerevisiae and a carboxy terminal ferredoxin domain. It was found that overexpression of this gene significantly enhances steroid hydroxylase activity of CYP11B2 expressing fission yeast cells. Moreover, the bacterially expressed ferredoxin domain of this protein can replace adrenodoxin in a reconstituted steroid hydroxylation assay and transfer electrons from adrenodoxin reductase to a mammalian or a bacterial cytochrome P450. Therefore, we suggest to name this protein etp1 (electron-transfer protein 1).

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Elevated plasma aldosterone levels play a detrimental role in certain forms of congestive heart failure and myocardial fibrosis. We proposed aldosterone synthase (CYP11B2) as a novel target for the treatment of these diseases. In this study, the synthesis and biological evaluation of substituted E- and Z-imidazolylmethylenetetrahydronaphthalenes and E- and Z-imidazolylmethyleneindanes (compounds 1a,b-9a,b) is described. The compounds were prepared by a Wittig-like reaction. They were tested for activity using bovine CYP11B and human CYP11B2 expressed in fission yeast and V79 MZh cells. Selectivity was determined toward human CYP11B1, CYP19, and CYP17. Especially in the case of CYP11B1 (steroid 11beta-hydroxylase), selectivity is a crucial issue, since sequence homology between this enzyme and the target enzyme is very high (93%). On the basis of the X-ray structure of human CYP2C9, a protein model of CYP11B2 was developed and docking experiments with the title compounds were performed. The biological results revealed highly potent inhibitors of CYP11B2 (IC(50) = 4-93 nM). The Z-isomers usually were more active than the corresponding E-isomers. Different inhibitory profiles could be observed: rather selective inhibitors of CYP11B1, dual inhibitors of both enzymes, and rather selective inhibitors of CYP11B2. The chloro derivative 8b was found to be a highly potent CYP11B2 inhibitor (IC(50) = 4 nM) showing a 5-fold selectivity for CYP11B1 (IC(50) = 20 nM). This compound could be an interesting lead for further optimization as a therapeutic agent. It also could be used as well as the CYP11B1 selective compounds as a pharmacological tool.