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

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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 β-amyrin-producing yeast cells, and the effect of the expressed CYP51H10 on β-amyrin metabolism in the host cells was examined. In the CYP51H10-introduced cells, β-amyrin was converted to a metabolite with 12,13-epoxy and one additional hydroxyl group. Since the 12,13-epoxy group introduced into β-amyrin ring is an essential structure of avenacin A-1, a triterpene glycoside produced in oat from β-amyrin, the present findings indicate the contribution of CYP51H10 to avenacin A-1 biosynthesis from β-amyrin. This is the first study showing a second function of the CYP51 family.