Structural Insights into Aldosterone Synthase Substrate Specificity and Targeted Inhibition

Abstract

Aldosterone is a major mineralocorticoid hormone that plays a key role in the regulation of electrolyte balance and blood pressure. Excess aldosterone levels can arise from dysregulation of the renin-angiotensin-aldosterone system and are implicated in the pathogenesis of hypertension and heart failure. Aldosterone synthase (cytochrome P450 11B2, CYP11B2) is the sole enzyme responsible for the production of aldosterone in humans. Blocking of aldosterone synthesis by mediating aldosterone synthase activity is thus a recently emerging pharmacological therapy for hypertension, yet a lack of structural information has limited this approach. Here, we present the crystal structures of human aldosterone synthase in complex with a substrate deoxycorticosterone and an inhibitor fadrozole. The structures reveal a hydrophobic cavity with specific features associated with corticosteroid recognition. The substrate binding mode, along with biochemical data, explains the high 11β-hydroxylase activity of aldosterone synthase toward both gluco- and mineralocorticoid formation. The low processivity of aldosterone synthase with a high extent of intermediates release might be one of the mechanisms of controlled aldosterone production from deoxycorticosterone. Although the active site pocket is lined by identical residues between CYP11B isoforms, most of the divergent residues that confer additional 18-oxidase activity of aldosterone synthase are located in the I-helix (vicinity of the O(2) activation path) and loops around the H-helix (affecting an egress channel closure required for retaining intermediates in the active site). This intrinsic flexibility is also reflected in isoform-selective inhibitor binding. Fadrozole binds to aldosterone synthase in the R-configuration, using part of the active site cavity pointing toward the egress channel. The structural organization of aldosterone synthase provides critical insights into the molecular mechanism of catalysis and enables rational design of more specific antihypertensive agents.

Structural Diversity of Eukaryotic Membrane Cytochrome P450s

“…Microsomal 21A2 catalyzes the 21-hydroxylation of 17␣-progesterone and progesterone to form precursors for the synthesis of cortisol by 11B1 and aldosterone by 11B2, respectively. The binding of deoxycorticosterone to mitochondrial 11B2 is similar to that of androstenedione in 19A1, but with C11 and the 18-methyl group placed near the heme iron (42).…”

Discovery of new 7-substituted-4-imidazolylmethyl coumarins and 4′-substituted-2-imidazolyl acetophenones open analogues as potent and selective inhibitors of steroid-11β-hydroxylase

“…Aromatase (CYP 19) [3][4][5] and 17β-hydroxylase/17,20-lyase (CYP17) [6] inhibitors are well known examples of CYPs inhibitors largely used in breast and prostate cancer, respectively (Chart 1). More recently, two additional CYP enzymes, namely, steroid 11β-hydroxylase (CYP11B1) [7][8][9][10] and aldosterone synthase (CYP11B2), [11][12][13] both involved in the biosynthesis of corticosteroid hormones, have been exploited as possible druggable targets. CYP11B1 catalyzes the last step of cortisol biosynthesis, that is the hydroxylation of 11-deoxycortisol to cortisol, whereas CYP11B2 catalyzes the conversion of 11-deoxycorticosterone to corticosterone, 18-hydroxycorticosterone and finally to aldosterone (Scheme 1).…”

The impact of the clinical CYP11B2 mutation V386A strongly depends on the enzyme’s genetic background

“…The beta-sheet 4 is assumed to represent a putative substrate recognition site, whereas the amino acid at position 173 is located in the D-helix, which is neither near the active site nor the adrenodoxin binding site. In order to obtain a deeper insight into the effect of the mutations on the CYP11B2 structure, we performed a computer analysis as described in the method section using the recently published CYP11B2 crystal structure [14]. Unfortunately, the results did not explain the effect of the variant 173…”