Protonation of a neutral (S)-β-bisabolene intermediate is involved in (S)-β-macrocarpene formation by the maize sesquiterpene synthases TPS6 and TPS11
Protonation of a neutral (S)-β-bisabolene intermediate is involved in (S)-β-macrocarpene formation by the maize sesquiterpene synthases TPS6 and TPS11
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DOI：
10.1074/jbc.m802682200
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发表时间：
2008-07-25
影响因子：
4.8
通讯作者：
Degenhardt, Joerg
中科院分区：
文献类型：
--
作者：
Koellner, Tobias G.;Schnee, Christiane;Degenhardt, Joerg
萜烯脱氢酶负责植物中发现的萜烯碳骨架的大量多样性。这些酶的独特的碳阳离子反应机制可以从单个异戊二烯基二磷酸底物形成多种产物。分离出两个玉米基因，它们编码非常相似的倍半萜烯脱氢酶，TPS 6和TPS 11，这两个基因都产生β-红没药烯（一种常见的单环倍半萜烯）和β-大卡宾（一种不常见的双环烯烃）。反应机理的研究表明，β-macrocarpene的形成是通过中性β-红没药烯中间体进行的，并且需要通过最终可能从水中提取的质子进行再质子化。这种再质子化依赖于pH和Mg 2+辅因子的存在。突变分析表明，在酶的活性中心的高度保守的酪氨酸残基是重要的质子化过程。TPS 6和TPS 11在玉米的根和叶中都有转录，但各自的萜烯产物仅在根中检测到。在根中的表达被植物取食伤害的叶片上调，表明叶和根之间的长距离信号传导级联。
Terpene synthases are responsible for the large diversity of terpene carbon skeletons found in plants. The unique, carbocationic reaction mechanism of these enzymes can form multiple products from a single prenyl diphosphate substrate. Two maize genes were isolated that encode very similar sesquiterpene synthases, TPS6 and TPS11, which both produce beta-bisabolene, a common monocyclic sesquiterpene, and beta-macrocarpene, an uncommon bicyclic olefin. Investigation of the reaction mechanism showed that the formation of beta-macrocarpene proceeds via a neutral beta-bisabolene intermediate and requires reprotonation by a proton that may ultimately be abstracted from water. This reprotonation is dependent on the pH and the presence of a Mg2+ cofactor. Mutational analysis of the enzyme demonstrated that a highly conserved tyrosine residue in the active center of the enzymes is important for the protonation process. TPS6 and TPS11 are transcribed both in leaves and roots of maize, but the respective terpene products were only detected in roots. The expression in roots was up-regulated by herbivore damage to the leaves, suggesting a long distance signal transduction cascade between leaves and roots.