Mogrosides, the major bioactive components isolated from the fruits of S. 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.
The Lab of Functional Sugar and Natural Bioactive Products led by Professor SUN Yuanxia at Tianjin Institute of Industrial Biotechnology (TIB), Chinese Academy of Sciences (CAS) reported the 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 in E. coli as a His-tag protein and it showed specificity for mogrol by transfer of a glucose moiety to the C-3 hydroxyl to form mogroside IE by in vitro enzymatic activity assays. The identification of CbQ and UGT from S. grosvenorii is important to synthesize mogrosides.
This work named "Functional Characterization of Cucurbitadienol Synthase and Triterpene Glycosyltransferase Involved in Biosynthesis of Mogrosides fromSiraitia grosvenorii"was supported by Tianjin Enterprise Postdoctoral Innovation Project Special Foundation, and had been published on the Journal of Plant Cell Physiology. Dai Longhai, a PhD graduate from TIB, is the first author of this paper.
Figure 1. Proposed biosynthetic pathway of mogrosides in S. grosvenorii. SE, squalene epoxidase; SgCbQ, cucurbitadienol synthase; P450s, cytochromes P450; UGTs, uridine diphosphate glycosyltransferases. Dark solid arrows represent one step; dark dotted arrows represent multiple steps.
