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Functional specialization of UDP ‐glycosyltransferase 73P12 in licorice to produce a sweet triterpenoid saponin, glycyrrhizin
Author(s) -
Nomura Yuhta,
Seki Hikaru,
Suzuki Tomonori,
Ohyama Kiyoshi,
Mizutani Masaharu,
Kaku Tomomi,
Tamura Keita,
Ono Eiichiro,
Horikawa Manabu,
Sudo Hiroshi,
Hayashi Hiroaki,
Saito Kazuki,
Muranaka Toshiya
Publication year - 2019
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.14409
Subject(s) - glycyrrhizin , glycyrrhiza uralensis , glucuronic acid , chemistry , biosynthesis , saponin , biochemistry , aglycone , triterpenoid saponin , glycoside , stereochemistry , biology , polysaccharide , enzyme , medicine , alternative medicine , pathology , pharmacology
Summary Glycyrrhizin, a sweet triterpenoid saponin found in the roots and stolons of Glycyrrhiza species (licorice), is an important active ingredient in traditional herbal medicine. We previously identified two cytochrome P450 monooxygenases, CYP 88D6 and CYP 72A154, that produce an aglycone of glycyrrhizin, glycyrrhetinic acid, in Glycyrrhiza uralensis . The sugar moiety of glycyrrhizin, which is composed of two glucuronic acids, makes it sweet and reduces its side‐effects. Here, we report that UDP ‐glycosyltransferase ( UGT ) 73P12 catalyzes the second glucuronosylation as the final step of glycyrrhizin biosynthesis in G . uralensis ; the UGT 73P12 produced glycyrrhizin by transferring a glucuronosyl moiety of UDP ‐glucuronic acid to glycyrrhetinic acid 3‐ O ‐monoglucuronide. We also obtained a natural variant of UGT 73P12 from a glycyrrhizin‐deficient (83‐555) strain of G . uralensis . The natural variant showed loss of specificity for UDP ‐glucuronic acid and resulted in the production of an alternative saponin, glucoglycyrrhizin. These results are consistent with the chemical phenotype of the 83‐555 strain, and suggest the contribution of UGT 73P12 to glycyrrhizin biosynthesis in planta . Furthermore, we identified Arg32 as the essential residue of UGT 73P12 that provides high specificity for UDP ‐glucuronic acid. These results strongly suggest the existence of an electrostatic interaction between the positively charged Arg32 and the negatively charged carboxy group of UDP ‐glucuronic acid. The functional arginine residue and resultant specificity for UDP ‐glucuronic acid are unique to UGT 73P12 in the UGT 73P subfamily. Our findings demonstrate the functional specialization of UGT 73P12 for glycyrrhizin biosynthesis during divergent evolution, and provide mechanistic insights into UDP ‐sugar selectivity for the rational engineering of sweet triterpenoid saponins.