title: Structural basis for inhibition of 17β-hydroxysteroid dehydrogenases by phytoestrogens: The case of fungal 17β-HSDcl.
abstract: Phytoestrogens are plant-derived compounds that functionally and structurally mimic mammalian estrogens. Phytoestrogens have broad inhibitory activities toward several steroidogenic enzymes, such as the 17β-hydroxysteroid dehydrogenases (17β-HSDs), which modulate the biological potency of androgens and estrogens in mammals. However, to date, no crystallographic data are available to explain phytoestrogens binding to mammalian 17β-HSDs. NADP(H)-dependent 17β-HSD from the filamentous fungus Cochliobolus lunatus (17β-HSDcl) has been the subject of extensive biochemical, kinetic and quantitative structure-activity relationship studies that have shown that the flavonols are the most potent inhibitors. In the present study, we investigated the structure-activity relationships of the ternary complexes between the holo form of 17β-HSDcl and the flavonols kaempferol and 3,7-dihydroxyflavone, in comparison with the isoflavones genistein and biochanin A. Crystallographic data are accompanied by kinetic analysis of the inhibition mechanisms for six flavonols (3-hydroxyflavone, 3,7-dihydroxyflavone, kaempferol, quercetin, fisetin, myricetin), one flavanone (naringenin), one flavone (luteolin), and two isoflavones (genistein, biochanin A). The kinetics analysis shows that the degree of hydroxylation of ring B significantly influences the overall inhibitory efficacy of the flavonols. A distinct binding mode defines the interactions between 17β-HSDcl and the flavones and isoflavones. Moreover, the complex with biochanin A reveals an unusual binding mode that appears to account for its greater inhibition of 17β-HSDcl with respect to genistein. Overall, these data provide a blueprint for identification of the distinct molecular determinants that underpin 17β-HSD inhibition by phytoestrogens.
authors.affiliation: Istituto di Cristallografia, UOS Trieste, Consiglio Nazionale delle Ricerche, S. S. 14-Km 163.5, I-34149, Trieste, Italy. Electronic address: alberto.cassetta@ts.ic.cnr.it.
authors.forename: Alberto
authors.initials: A
authors.lastname: Cassetta
authors.affiliation: Institute of Biochemistry, Faculty of Medicine, University of Ljubljana, Vrazov trg 2, SI-1000 Ljubljana, Slovenia. Electronic address: stojan@mf.uni-lj.si.
authors.forename: Jure
authors.initials: J
authors.lastname: Stojan
authors.affiliation: Structural Biology Laboratory, Elettra-Sincrotrone Trieste S. C. p. A., S. S. 14-Km 163.5, I-34149, Trieste, Italy.
authors.forename: Ivet
authors.initials: I
authors.lastname: Krastanova
authors.affiliation: Institute of Biochemistry, Faculty of Medicine, University of Ljubljana, Vrazov trg 2, SI-1000 Ljubljana, Slovenia.
authors.forename: Katja
authors.initials: K
authors.lastname: Kristan
authors.affiliation: Institute of Biochemistry, Faculty of Medicine, University of Ljubljana, Vrazov trg 2, SI-1000 Ljubljana, Slovenia.
authors.forename: Mojca
authors.initials: M
authors.lastname: Brunskole Švegelj
authors.affiliation: Istituto di Cristallografia, UOS Trieste, Consiglio Nazionale delle Ricerche, S. S. 14-Km 163.5, I-34149, Trieste, Italy.
authors.forename: Doriano
authors.initials: D
authors.lastname: Lamba
authors.affiliation: Institute of Biochemistry, Faculty of Medicine, University of Ljubljana, Vrazov trg 2, SI-1000 Ljubljana, Slovenia.
authors.forename: Tea
authors.initials: T
authors.lastname: Lanišnik Rižner
mesh_terms: D015067:17-Hydroxysteroid Dehydrogenases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001203:Ascomycota / Q000201:enzymology*; D001665:Binding Sites; D055162:Biocatalysis; D018360:Crystallography, X-Ray; D030562:Databases, Protein; D019587:Dietary Supplements; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism*; D005419:Flavonoids / Q000737:chemistry / Q000378:metabolism*; D005656:Fungal Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019833:Genistein / Q000737:chemistry / Q000378:metabolism; D020035:Holoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006900:Hydroxylation; D044949:Kaempferols / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008968:Molecular Conformation; D048789:Phytoestrogens / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D004791:Enzyme Inhibitors; D005419:Flavonoids; D005656:Fungal Proteins; D020035:Holoenzymes; D044949:Kaempferols; D048789:Phytoestrogens; D011994:Recombinant Proteins; C006552:kaempferol; D019833:Genistein; D015067:17-Hydroxysteroid Dehydrogenases; C422925:3,7-dihydroxyflavone; C004541:biochanin A
keywords: Enzyme inhibition kinetics; Flavonoids; Hydroxysteroid dehydrogenases; Phytoestrogens; Structural biology; Structure–activity relationships