College of Biotechnology and Pharmaceutical Engineering, Nanjing Tech University, Nanjing, 211800, China.
Appl Biochem Biotechnol. 2021 Mar;193(3):637-649. doi: 10.1007/s12010-020-03439-y. Epub 2020 Oct 15.
Rebaudioside E, one of the minor components of steviol glycosides, was first isolated and identified from Stevia rebaudiana in 1977. It is a high-intensity sweetener that tastes about 150-200 times sweeter than sucrose and is also a precursor for biosynthesis of rebaudioside D and rebaudioside M, the next-generation Stevia sweeteners. In this work, new unknown steviol glycosides were enzymatically synthesized from stevioside by coupling UDP-glucosyltransferase UGTSL2 from Solanum lycopersicum and sucrose synthase StSUS1 from Solanum tuberosum. Rebaudioside E was speculated to be the main product of glucosylation of the Glc(β1→C-19) residue of stevioside along with the formation of a (β1→2) linkage based on the analysis of the regioselectivity and stereoselectivity of UGTSL2, and verified afterwards by LC-MS/MS with standard. In a 20-ml bioconversion reaction of 20 g/l stevioside by UGTSL2 and StSUS1, 15.92 g/l rebaudioside E was produced for 24 h.
甜菊糖苷 E 是甜菊糖的微量成分之一，于 1977 年首次从甜叶菊中分离鉴定得到。它是一种高强度甜味剂，甜度约为蔗糖的 150-200 倍，也是合成下一代甜菊糖莱鲍迪苷 D 和莱鲍迪苷 M 的前体。在这项工作中，我们通过将番茄中的 UDP-葡萄糖基转移酶 UGTSL2 和土豆中的蔗糖合酶 StSUS1 与甜菊苷偶联，从甜菊苷中酶促合成了新的未知甜菊糖苷。根据 UGTSL2 的区域选择性和立体选择性分析，推测甜菊糖苷的 Glc(β1→C-19)残基的葡糖基化主要产物是甜菊糖苷 E，同时形成（β1→2）键，随后通过与标准品的 LC-MS/MS 验证。在 UGTSL2 和 StSUS1 对 20g/L 甜菊苷进行的 20ml 生物转化反应中，24 小时内生成了 15.92g/L 的甜菊糖苷 E。
