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A novel glucuronosyltransferase has an unprecedented ability to catalyse continuous two‐step glucuronosylation of glycyrrhetinic acid to yield glycyrrhizin
Author(s) -
Xu Guojie,
Cai Wei,
Gao Wei,
Liu Chunsheng
Publication year - 2016
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.14039
Subject(s) - glycyrrhizin , glycyrrhiza uralensis , glycosyltransferase , biosynthesis , biochemistry , glucuronosyltransferase , chemistry , enzyme , transcriptome , biology , gene , gene expression , pharmacology , medicine , alternative medicine , pathology , microsome
Summary Glycyrrhizin is an important bioactive compound that is used clinically to treat chronic hepatitis and is also used as a sweetener world‐wide. However, the key UDP‐dependent glucuronosyltransferases (UGATs) involved in the biosynthesis of glycyrrhizin remain unknown. To discover unknown UGATs, we fully annotated potential UGATs from Glycyrrhiza uralensis using deep transcriptome sequencing. The catalytic functions of candidate UGATs were determined by an in vitro enzyme assay. Systematically screening 434 potential UGATs, we unexpectedly found one unique Gu UGAT that was able to catalyse the glucuronosylation of glycyrrhetinic acid to directly yield glycyrrhizin via continuous two‐step glucuronosylation. Expression analysis further confirmed the key role of Gu UGAT in the biosynthesis of glycyrrhizin. Site‐directed mutagenesis revealed that Gln‐352 may be important for the initial step of glucuronosylation, and His‐22, Trp‐370, Glu‐375 and Gln‐392 may be important residues for the second step of glucuronosylation. Notably, the ability of Gu UGAT to catalyse a continuous two‐step glucuronosylation reaction was determined to be unprecedented among known glycosyltransferases of bioactive plant natural products. Our findings increase the understanding of traditional glycosyltransferases and pave the way for the complete biosynthesis of glycyrrhizin.