Human CYP27A1 catalyzes hydroxylation of ß-sitosterol and ergosterol.

ß-Sitosterol and ergosterol are the equivalents of cholesterol in plants and fungi, respectively, and common sterols in the human diet. In the current work, both were identified as novel CYP27A1 substrates by in vitro experiments applying purified human CYP27A1 and its redox partners adrenodoxin (Adx) and adrenodoxin reductase (AdR). A Bacillus megaterium based biocatalyst recombinantly expressing the same proteins was utilized for the conversion of the substrates to obtain sufficient amounts of the novel products for a structural NMR analysis. ß-Sitosterol was found to be converted into 26-hydroxy-ß-sitosterol and 29-hydroxy-ß-sitosterol, whereas ergosterol was converted into 24-hydroxyergosterol, 26-hydroxyergosterol and 28-hydroxyergosterol.