title: Licorice beta-amyrin 11-oxidase, a cytochrome P450 with a key role in the biosynthesis of the triterpene sweetener glycyrrhizin.
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.
authors.affiliation: Kihara Institute for Biological Research, Yokohama City University, Maioka-cho 641-12, Totsuka-ku, Yokohama, Kanagawa 244-0813, Japan.
authors.forename: Hikaru
authors.initials: H
authors.lastname: Seki
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Ohyama
authors.forename: Satoru
authors.initials: S
authors.lastname: Sawai
authors.forename: Masaharu
authors.initials: M
authors.lastname: Mizutani
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Ohnishi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sudo
authors.forename: Tomoyoshi
authors.initials: T
authors.lastname: Akashi
authors.forename: Toshio
authors.initials: T
authors.lastname: Aoki
authors.forename: Kazuki
authors.initials: K
authors.lastname: Saito
authors.forename: Toshiya
authors.initials: T
authors.lastname: Muranaka
mesh_terms: D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D006035:Glycyrrhiza / Q000201:enzymology / Q000235:genetics; D019695:Glycyrrhizic Acid / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010802:Phylogeny; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D013549:Sweetening Agents / Q000737:chemistry / Q000378:metabolism*
chemical_list: D013549:Sweetening Agents; D019695:Glycyrrhizic Acid; D003577:Cytochrome P-450 Enzyme System
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