Ministry of Education, Key Laboratory of Saline-alkali Vegetation Ecology Restoration, Northeast Forestry University, Harbin, PR China.
Heilongjiang Key Laboratory of Plant Bioactive Substance Biosynthesis and Utilization, Northeast Forestry University, Harbin, PR China.
Crit Rev Biochem Mol Biol. 2022 Apr;57(2):113-132. doi: 10.1080/10409238.2021.1979458. Epub 2021 Oct 2.
Triterpenoids are one of the largest groups of secondary metabolites and exhibit diverse structures, which are derived from C30 skeletons that are biosynthesized the isoprenoid pathway by cyclization of 2,3-oxidosqualene. Triterpenoids have a wide range of biological activities, and are used in functional foods, drugs, and as industrial materials. Due to the low content levels in their native plants and limited feasibility and efficiency of chemical synthesis, heterologous biosynthesis of triterpenoids is the most promising strategy. Herein, we classified 121 triterpene alcohols/ketones according to their conformation and ring numbers, among which 51 skeletons have been experimentally characterized as the products of oxidosqualene cyclases (OSCs). Interestingly, 24 skeletons that have not been reported from nature source were generated by OSCs in heterologous expression. Comprehensive evolutionary analysis of the identified 152 OSCs from 75 species in 25 plant orders show that several pentacyclic triterpene synthases repeatedly originated in multiple plant lineages. Comparative analysis of OSC catalytic reaction revealed that stabilization of intermediate cations, steric hindrance, and conformation of active center amino acid residues are primary factors affecting triterpene formation. Optimization of OSC could be achieved by changing of side-chain orientations of key residues. Recently, methods, such as rationally design of pathways, regulation of metabolic flow, compartmentalization engineering, etc., were introduced in improving chassis for the biosynthesis of triterpenoids. We expect that extensive study of natural variation of large number of OSCs and catalytical mechanism will provide basis for production of high level of triterpenoids by application of synthetic biology strategies.
三萜类化合物是最大的次生代谢产物之一，具有多样的结构，它们来源于 C30 骨架，通过 2,3-氧化鲨烯的环化由异戊烯途径生物合成。三萜类化合物具有广泛的生物活性，被用于功能性食品、药物和工业材料。由于其在天然植物中的含量水平低，以及化学合成的可行性和效率有限，因此异源生物合成三萜类化合物是最有前途的策略。在此，我们根据构象和环数对 121 种三萜醇/酮进行了分类，其中 51 种骨架已被实验确认为氧化鲨烯环化酶（OSC）的产物。有趣的是，在异源表达中，OSC 产生了 24 种从未在自然界中报道过的骨架。对来自 25 个植物目 75 个物种的 152 种 OSC 的综合进化分析表明，几种五环三萜合酶在多个植物谱系中反复起源。对 OSC 催化反应的比较分析表明，中间阳离子的稳定化、空间位阻和活性中心氨基酸残基的构象是影响三萜形成的主要因素。通过改变关键残基的侧链取向，可以优化 OSC。最近，人们引入了一些方法，如途径的合理设计、代谢流的调节、分隔工程等，以改善底盘用于三萜类化合物的生物合成。我们期望对大量 OSC 的自然变异和催化机制进行广泛研究，为应用合成生物学策略生产高水平的三萜类化合物提供基础。
