Abstract
Legumes show a pool of different and pharmacologically important triterpenoid saponins. Most of them are biosynthesized from the universal precursor β-amyrin. Recently, CYP93E1 and CYP93E3, two cytochrome P450s obtained from soybean and licorice respectively, were identified as β-amyrin-24-hydroxylases in the soyasapogenol biosynthesis. A homolog (CYP93E2) obtained from the model legume Medicago truncatula showed an 80% of amino acid identity to these enzymes. Additionally, using the Medicago truncatula co-expression analysis; CYP93E2 was found to be highly co-expressed with β-amyrin synthase (bAS) (correlation coefficient: 0.77). When its β-amyrin oxidizing potential activity was tested using a yeast expression system, it showed β-amyrin-24-hydroxylase activity. Furthermore, a new P450 showed higher correlation with bAS (correlation coefficient: 0.85) compared to CYP93E2. The β-amyrin oxidizing potential activity was also tested in the previously used yeast expression system, showing its ability to modify β-amyrin to the ubiquitous and pharmacologically important triterpenoid, oleanolic acid.
