2025-09-24 中国科学院（CAS）
＜関連情報＞
- https://english.cas.cn/newsroom/research_news/chem/202509/t20250924_1055258.shtml
- https://www.pnas.org/doi/10.1073/pnas.2504698122
Sr UGT76G4の特性評価により、位置選択性と効率的なReb M合成のための重要な残基が明らかになった Characterization of SrUGT76G4 reveals a key residue for regioselectivity and efficient Reb M synthesis
Yu Wang, Tang Li, Yangjie Zheng, +5 , and Heng Yin
Proceedings of the National Academy of Sciences Published:September 17, 2025
DOI:https://doi.org/10.1073/pnas.2504698122
Significance
Steviol glycosides (SGs) are plant-derived sweeteners from Stevia rebaudiana with applications in dietary sugar reduction. Rebaudioside M (Reb M) is the most desirable SG due to its superior taste profile, but its low natural abundance limits commercial production. This study identifies UGT76G4, a Stevia glycosyltransferase with a strong preference for C19 glycosylation, enabling efficient conversion of Reb D to Reb M. Structural and biochemical analyses reveal key residues governing regioselectivity, guiding protein engineering to further enhance Reb M yield. These findings deepen our understanding of SG biosynthesis in Stevia and provide a promising enzyme for sustainable Reb M production, advancing biotechnological strategies for steviol glycoside biosynthesis, and optimizing plant metabolic engineering approaches.
Abstract
Steviol glycosides (SGs) from Stevia rebaudiana are prized as noncaloric sweeteners, with rebaudioside M (Reb M)—a next-generation SG known for its sucrose-like sweetness and lack of off-tastes—standing out for its superior sensory profile. However, Reb M’s limited natural abundance impedes its commercial production. Here, we report the identification of a glucosyltransferase, UGT76G4 that efficiently catalyzes the conversion of Reb D to Reb M with a strong preference for C19 glycosylation. Structural and functional analyses, including X-ray crystallography, molecular dynamics simulations, and mutagenesis, revealed key residues in UGT76G4 that dictate its regioselectivity, with residue 200 playing a pivotal role. Engineered UGT76G4 variants, including Q199I/G200Y and H155S/Q199I/G200Y, enhanced Reb E and Reb D conversion efficiency by 1.46-fold and 23-fold, respectively, compared to UGT76G1. The engineered variants offer a promising pathway for increasing Reb M production, advancing biotechnological strategies for steviol glycoside biosynthesis and optimizing plant metabolic engineering approaches. Our findings deepen the understanding of SG biosynthesis and provide a basis for sustainable production of high-value sweeteners.
