?Functional Characterization of Cucurbitadienol Synthase and Triterpene Glycosyltransferase Involved in Biosynthesis of Mogrosides fromSiraitia grosvenorii

Longhai Dai, Can Liu, Yueming Zhu, Jiangsheng Zhang, Yan Men and Yuanxia Sun

Abstract

Mogrosides, the major bioactive components isolated from the fruits ofSiraitia grosvenorii, are a family of cucurbitane-type tetracyclic triterpenoid saponins that are used worldwide as high-potency sweeteners and possess a variety of notable pharmacological activities. Mogrosides are synthesized from 2,3-oxidosqualene via a series of reactions catalyzed by cucurbitadienol synthase (CbQ), cytochromes P450 (P450s), and uridine diphosphate glycosyltransferases (UGTs) in vivo. However, relevant genes have not been characterized to date. In this study, we report successful identification of SgCbQ and UGT74AC1, which were previously predicted via RNA-sequencing (RNA-seq) and digital gene expression profile (DGE) analysis of the fruits of S. grosvenorii. SgCbQ was functionally characterized by expression in the lanosterol synthase-deficient yeast strain GIL77 and was found to accumulate cucurbitadienol as the sole product. UGT74AC1 was heterologously expressed inEscherichia coli as a His-tag protein and it showed specificity for mogrol 

mogroside IIE, mogroside III, mogroside IV, siamenoside I and
mogroside V) were purchased from Chengdu Biopurify Phytochemicals.