Direct formation of the sesquiterpeonid ether liguloxide by a terpene synthase in Senecio scandens
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Direct formation of the sesquiterpeonid ether liguloxide by a terpene synthase in Senecio scandens Liping Wang1 · Jin Liang1 · Xin Xie1 · Jiang Liu1,2 · Qinqin Shen1 · Lixia Li3 · Qiang Wang1,2 Received: 20 April 2020 / Accepted: 1 September 2020 © Springer Nature B.V. 2020
Abstract Key message SsLOS directly catalyzed formation of the sesquiterpenoid ether liguloxide in the medicinal plant Senecio scandens. Abstract Terpene synthases determine the diversity of terpene skeletons and corresponding terpenoid natural products. Oxygenated groups introduced in catalysis of terpene synthases are important for solubility, potential bioactivity and further elaboration of terpenoids. Here we identified one terpene synthase, SsLOS, in the Chinese medicinal plant Senecio scandens. SsLOS acted as the sesquiterpene synthase and utilized (E,E)-farnesyl diphosphate as the substrate to produce a blend of sesquiterpenoids. GC–MS analysis and NMR structure identification demonstrated that SsLOS directly produced the sesquiterpenoid ether, liguloxide, as well as its alcoholic isomer, 6-epi-guaia-2(3)-en-11-ol. Homology modeling and site-directed mutagenesis were combined to explore the catalytic mechanism of SsLOS. A few key residues were identified in the active site and hedycaryol was identified as the neutral intermediate of SsLOS catalysis. The plausible catalytic mechanism was proposed as well. Altogether, SsLOS was identified and characterized as the sesquiterpenoid ether synthase, which is the second terpenoid ether synthase after 1,8-cineol synthase, suggesting some insights for the universal mechanism of terpene synthases using the water molecule in the catalytic cavity. Keywords Liguloxide · Medicinal plant · Sesquiternoid · Terpene synthase · Water
Introduction Among abundant natural products, terpenoids have the most diverse structures and are widely utilized in the world. Some terpenoids are only comprised of hydrogen and carbon elements, and others are elaborated diversely with oxygenated groups (Christianson 2017). Diversity of terpenoids is firstly Liping Wang and Jin Liang have contributed equally. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11103-020-01068-x) contains supplementary material, which is available to authorized users. * Qiang Wang [email protected] 1
Institute of Ecological Agriculture, Sichuan Agricultural University, Chengdu 611130, China
2
State Key Laboratory of Crop Gene Exploration and Utilization in Southwest China, Chengdu 611130, China
3
College of Veterinary Medicine, Sichuan Agricultural University, Chengdu 611130, China
determined by terpene synthases. Terpenoid biosynthesis is initiated with dephosphorylation of the phosphate substrates, such as geranyl diphosphate (GPP), farnesyl diphosphate (FPP) and geranylgeranyl diphosphate (GGPP). Terpene synthases catalyze complicated reactions such as dephosphorylation, protonation, cyclization, proton/methyl migration to generate a series of carbocation intermediates for f
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