Oxidation of Cucurbitadienol Catalyzed by CYP87D18 in the Biosynthesis of Mogrosides From Siraitia Grosvenorii

Plant Cell Physiol. 2016 May;57(5):1000-7. doi: 10.1093/pcp/pcw038. Epub 2016 Feb 21.

Abstract

Mogrosides, the principally bioactive compounds extracted from the fruits of Siraitia grosvenorii, are a group of glycosylated cucurbitane-type tetracyclic triterpenoid saponins that exhibit a wide range of notable biological activities and are commercially available worldwide as natural sweeteners. The biosynthesis of mogrosides involves initial cyclization of 2,3-oxidosqualene to the triterpenoid skeleton of cucurbitadienol, followed by a series of oxidation reactions catalyzed by Cyt P450s (P450s) and then glycosylation reactions catalyzed by UDP glycosyltransferases (UGTs). We previously reported the identification of a cucurbitadienol synthase (SgCbQ) and a mogrol C-3 hydroxyl glycosyltransferase (UGT74AC1). However, molecular characterization of further transformation of cucurbitadienol to mogrol by P450s remains unavailable. In this study, we report the successful identification of a multifunctional P450 (CYP87D18) as being involved in C-11 oxidation of cucurbitadienol. In vitro enzymatic activity assays showed that CYP87D18 catalyzed the oxidation of cucurbitadienol at C-11 to produce 11-oxo cucurbitadienol and 11-hydroxy cucurbitadienol. Furthermore, 11-oxo-24,25-epoxy cucurbitadienol as well as 11-oxo cucurbitadienol and 11-hydroxy cucurbitadienol were produced when CYP87D18 was co-expressed with SgCbQ in genetic yeast, and their structures were confirmed by liquid chromatography-solid-phase extraction-nuclear magnetic resonance-mass spectrometry coupling (LC-SPE-NMR-MS). Taken together, these results suggest a role for CYP87D18 as a multifunctional cucurbitadienol oxidase in the mogrosides pathway.

Keywords: CYP87D18; Cucurbitadienol; Cytochrome P450; Mogrosides; Siraitia grosvenorii.

MeSH terms

  • Biosynthetic Pathways
  • Catalysis
  • Cucurbitaceae / enzymology*
  • Cucurbitaceae / genetics
  • Cytochrome P-450 Enzyme System / genetics
  • Cytochrome P-450 Enzyme System / metabolism
  • Fruit / enzymology
  • Fruit / genetics
  • Gene Expression
  • Glycosides / metabolism*
  • Glycosyltransferases / genetics
  • Glycosyltransferases / metabolism
  • Oxidation-Reduction
  • Plant Proteins / genetics
  • Plant Proteins / metabolism*
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae / metabolism
  • Saponins / metabolism
  • Squalene / analogs & derivatives
  • Squalene / metabolism
  • Triterpenes / metabolism*

Substances

  • 2,3-oxidosqualene
  • Glycosides
  • Plant Proteins
  • Saponins
  • Triterpenes
  • cucurbitane
  • Squalene
  • Cytochrome P-450 Enzyme System
  • Glycosyltransferases