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

Human cytochrome P450 11B2 (CYP11B2) is an essential enzyme in the steroid hormone biosynthesis, which catalyzes the last three reaction steps of the aldosterone synthesis. These reactions comprise a hydroxylation at position C11 of the steroid intermediate deoxycorticosterone yielding corticosterone, followed by a hydroxylation at position C18 yielding 18-hydroxy-corticosterone and a subsequent oxidation of the hydroxyl group at C18, which results in the formation of aldosterone. Alterations in the amino acid sequence of CYP11B2 often cause severe disease patterns. We previously described a procedure for expression and purification of human CYP11B2 employing recombinant E. coli, which allows the rapid characterization of CYP11B2 mutants on a molecular level. This system was now utilized for the examination of the influence of the polymorphism at position 173 in combination with the mutation V386A on the activity of CYP11B2. Our in vitro findings show that the combination of the V386A mutation with the variant CYP11B2 173 only slightly reduces the 18-hydroxylase and 18-oxidase activity, whereas the V386A mutation with the CYP11B2 173 variant almost abolishes the 18-hydroxylation and 18-oxidation. In both cases the 11-hydroxylase activity is not affected. These findings highlight the importance of the genetic background of an enzyme when regarding the effect of clinical mutations.