Oxidation and cyclization of casbene in the biosynthesis of Euphorbia factors from mature seeds of Euphorbia lathyris L.
Oxidation and cyclization of casbene in the biosynthesis of Euphorbia factors from mature seeds of Euphorbia lathyris L.
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DOI：
10.1073/pnas.1607504113
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发表时间：
2016-08-23
影响因子：
11.1
通讯作者：
Hamberger, Bjoern
中科院分区：
文献类型：
--
作者：
Luo, Dan;Callari, Roberta;Hamberger, Bjoern
大戟种子油中含有一系列被称为大戟因子的大环二萜类化合物。它们是目前工业上美丁酸吲哚的来源，该药被批准用于治疗光化性角化病，一种癌前皮肤病。在这里，我们报道了乙醇脱氢酶介导的环化步骤，在大戟因子的生物合成途径，说明了分子内碳-碳键的起源存在于芳烃和金刚烷二萜类化合物。这种非传统的环化反应描述了大环二萜酪宾的环闭合。通过对成熟种子的转录分析和植物功能鉴定，我们鉴定了参与酪蛋白环化反应的三种酶。这些酶包括来自CYP71家族的两个细胞色素P450和一个酒精脱氢酶(ADH)。CYP71D445和CYP726A27分别催化酪宾的区域特异性9-氧化和5-氧化。当与这些P450催化的单加氧反应结合时，莱氏乳杆菌ADH1催化羟基脱氢，导致随后的重排和环化。这种非常规环化反应的发现可能为全面阐明吲哚甲丁酸酯和其他具有生物活性的大环二萜类化合物的生物合成途径提供关键环节。
The seed oil of Euphorbia lathyris L. contains a series of macrocyclic diterpenoids known as Euphorbia factors. They are the current industrial source of ingenol mebutate, which is approved for the treatment of actinic keratosis, a precancerous skin condition. Here, we report an alcohol dehydrogenase-mediated cyclization step in the biosynthetic pathway of Euphorbia factors, illustrating the origin of the intramolecular carbon-carbon bonds present in lathyrane and ingenane diterpenoids. This unconventional cyclization describes the ring closure of the macrocyclic diterpene casbene. Through transcriptomic analysis of E. lathyris L. mature seeds and in planta functional characterization, we identified three enzymes involved in the cyclization route from casbene to jolkinol C, a lathyrane diterpene. These enzymes include two cytochromes P450 from the CYP71 clan and an alcohol dehydrogenase (ADH). CYP71D445 and CYP726A27 catalyze regio-specific 9-oxidation and 5-oxidation of casbene, respectively. When coupled with these P450-catalyzed monooxygenations, E. lathyris ADH1 catalyzes dehydrogenation of the hydroxyl groups, leading to the subsequent rearrangement and cyclization. The discovery of this nonconventional cyclization may provide the key link to complete elucidation of the biosynthetic pathways of ingenol mebutate and other bioactive macrocyclic diterpenoids.