Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1, Yamadaoka, Suita, Osaka, 565-0871, Japan.
RIKEN Center for Sustainable Resource Science, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa, 230-0045, Japan.
Nat Commun. 2020 Nov 16;11(1):5664. doi: 10.1038/s41467-020-19399-0.
Triterpenoid saponins are specialised metabolites distributed widely in the plant kingdom that consist of one or more sugar moieties attached to triterpenoid aglycones. Despite the widely accepted view that glycosylation is catalysed by UDP-dependent glycosyltransferase (UGT), the UGT which catalyses the transfer of the conserved glucuronic acid moiety at the C-3 position of glycyrrhizin and various soyasaponins has not been determined. Here, we report that a cellulose synthase superfamily-derived glycosyltransferase (CSyGT) catalyses 3-O-glucuronosylation of triterpenoid aglycones. Gene co-expression analyses of three legume species (Glycyrrhiza uralensis, Glycine max, and Lotus japonicus) reveal the involvement of CSyGTs in saponin biosynthesis, and we characterise CSyGTs in vivo using Saccharomyces cerevisiae. CSyGT mutants of L. japonicus do not accumulate soyasaponin, but the ectopic expression of endoplasmic reticulum membrane-localised CSyGTs in a L. japonicus mutant background successfully complement soyasaponin biosynthesis. Finally, we produced glycyrrhizin de novo in yeast, paving the way for sustainable production of high-value saponins.
三萜皂苷是广泛分布于植物界的特异性代谢产物，由连接在三萜苷元上的一个或多个糖基组成。尽管人们普遍认为糖基化是由 UDP 依赖性糖基转移酶 (UGT) 催化的，但催化甘草酸和各种大豆皂苷 C-3 位上保守的葡萄糖醛酸基转移的 UGT 尚未确定。在这里，我们报告了一种纤维素合酶超家族衍生的糖基转移酶 (CSyGT) 催化三萜苷元的 3-O-葡萄糖醛酸化。对三种豆科植物（甘草、大豆和百脉根）的基因共表达分析表明 CSyGT 参与了皂苷的生物合成，我们使用酿酒酵母对 CSyGT 进行了体内研究。百脉根的 CSyGT 突变体不能积累大豆皂苷，但内质网定位的 CSyGT 在百脉根突变体背景下的异位表达成功地补充了大豆皂苷的生物合成。最后，我们在酵母中从头合成了甘草酸，为高价值皂苷的可持续生产铺平了道路。
