Licorice Beta-Amyrin 11-oxidase, a Cytochrome P450 With a Key Role in the Biosynthesis of the Triterpene Sweetener Glycyrrhizin

Proc Natl Acad Sci U S A. 2008 Sep 16;105(37):14204-9. doi: 10.1073/pnas.0803876105. Epub 2008 Sep 8.

Abstract

Glycyrrhizin, a major bioactive compound derived from the underground parts of Glycyrrhiza (licorice) plants, is a triterpene saponin that possesses a wide range of pharmacological properties and is used worldwide as a natural sweetener. Because of its economic value, the biosynthesis of glycyrrhizin has received considerable attention. Glycyrrhizin is most likely derived from the triterpene beta-amyrin, an initial product of the cyclization of 2,3-oxidosqualene. The subsequent steps in glycyrrhizin biosynthesis are believed to involve a series of oxidative reactions at the C-11 and C-30 positions, followed by glycosyl transfers to the C-3 hydroxyl group; however, no genes encoding relevant oxidases or glycosyltransferases have been identified. Here we report the successful identification of CYP88D6, a cytochrome P450 monooxygenase (P450) gene, as a glycyrrhizin-biosynthetic gene, by transcript profiling-based selection from a collection of licorice expressed sequence tags (ESTs). CYP88D6 was characterized by in vitro enzymatic activity assays and shown to catalyze the sequential two-step oxidation of beta-amyrin at C-11 to produce 11-oxo-beta-amyrin, a possible biosynthetic intermediate between beta-amyrin and glycyrrhizin. CYP88D6 coexpressed with beta-amyrin synthase in yeast also catalyzed in vivo oxidation of beta-amyrin to 11-oxo-beta-amyrin. CYP88D6 expression was detected in the roots and stolons by RT-PCR; however, no amplification was observed in the leaves or stems, which is consistent with the accumulation pattern of glycyrrhizin in planta. These results suggest a role for CYP88D6 as a beta-amyrin 11-oxidase in the glycyrrhizin pathway.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cytochrome P-450 Enzyme System / metabolism*
  • Gas Chromatography-Mass Spectrometry
  • Gene Expression Regulation, Enzymologic
  • Gene Expression Regulation, Plant
  • Glycyrrhiza / enzymology
  • Glycyrrhiza / genetics
  • Glycyrrhizic Acid / chemistry
  • Glycyrrhizic Acid / metabolism*
  • Molecular Sequence Data
  • Molecular Structure
  • Oxidation-Reduction
  • Phylogeny
  • Saccharomyces cerevisiae / enzymology
  • Saccharomyces cerevisiae / genetics
  • Sweetening Agents / chemistry
  • Sweetening Agents / metabolism*

Substances

  • Sweetening Agents
  • Glycyrrhizic Acid
  • Cytochrome P-450 Enzyme System

Associated data

  • GENBANK/AB433175
  • GENBANK/AB433176
  • GENBANK/AB433177
  • GENBANK/AB433178
  • GENBANK/AB433179
  • GENBANK/AB433810
  • GENBANK/AB437320