β-Amyrin Oxidation by Oat CYP51H10 Expressed Heterologously in Yeast Cells: The First Example of CYP51-Dependent Metabolism Other than the 14-Demethylation of Sterol Precursors

CYP51 has been recognized as a unique CYP family that consists of one isolated molecular species, a sterol 14-demethylase essential for sterol biosynthesis. However, another CYP51 gene classified as the CYP51H subfamily has been identified in higher plants, in addition to a sterol 14-demethylase gene, CYP51G1. To shed light on the function of this "second CYP51", oat CYP51H10 was introduced into the beta-amyrin-producing yeast cells, and the effect of the expressed CYP51H10 on beta-amyrin metabolism in the host cells was examined. In the CYP51H10-introduced cells, beta-amyrin was converted to a metabolite with 12,13-epoxy and one additional hydroxyl group. Since the 12,13-epoxy group introduced into beta-amyrin ring is an essential structure of avenacin A-1, a triterpene glycoside produced in oat from beta-amyrin, the present findings indicate the contribution of CYP51H10 to avenacin A-1 biosynthesis from beta-amyrin. This is the first study showing a second function of the CYP51 family.