Institute for Synthetic Biosystem/Department of Biochemical Engineering, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, China.
School of Life Science, Beijing Institute of Technology, Beijing 100081, China.
J Agric Food Chem. 2020 Aug 12;68(32):8580-8588. doi: 10.1021/acs.jafc.0c03842. Epub 2020 Jul 31.
Glycyrrhetinic acid (GA), a pentacyclic triterpenoid aglycone, is the major functional component in licorice which mainly exists in the form of functional glycosides in licorice. The introduction of a sugar moiety to the C-3 OH of GA to yield glycosylated derivatives has been reported, but the late-stage glycosylation of GA-3--sugar to form rare GA glycosides with more complexed glycosyl decoration has been rarely reported. In this study, a unique UDP-galactosyltransferase GmSGT2 from was found to transfer a galactose to the C2 position of the sugar moiety of GA-3--monoglucuronide (GAMG) and GA-3--monoglucose. In addition to UDP-galactose, GmSGT2 also recognizes UDP-glucose, UDP-xylose, and UDP-arabinose with relative activities of 32.1-89.2%. Based on a test of 12 typical natural products, GmSGT2 showed high specificity toward the pentacyclic triterpenoid skeleton as the sugar acceptor. Molecular docking was performed to elucidate the substrate recognition mechanism of GmSGT2 toward GAMG.
甘草次酸（GA）是一种五环三萜类化合物，是甘草中的主要功能成分，主要以甘草功能糖苷的形式存在。已报道将糖基引入 GA 的 C-3 OH 以生成糖基化衍生物，但 GA-3--糖的后期糖基化形成具有更复杂糖基修饰的罕见 GA 糖苷的报道很少。在这项研究中，从 中发现了一种独特的 UDP-半乳糖基转移酶 GmSGT2，它将半乳糖转移到 GA-3--单葡萄糖醛酸苷（GAMG）和 GA-3--单葡萄糖的糖基的 C2 位置。除了 UDP-半乳糖外，GmSGT2 还能识别 UDP-葡萄糖、UDP-木糖和 UDP-阿拉伯糖，相对活性为 32.1-89.2%。基于对 12 种典型天然产物的测试，GmSGT2 对戊环三萜骨架作为糖受体表现出很高的特异性。进行了分子对接以阐明 GmSGT2 对 GAMG 的底物识别机制。
