Institute of Biological Chemistry, Academia Sinica, Taipei115, Taiwan R.O.C.
Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, Los Angeles, CA, 90095, USA.
Angew Chem Int Ed Engl. 2017 Aug 1;56(32):9478-9482. doi: 10.1002/anie.201705501. Epub 2017 Jul 6.
The okaramines are a class of complex indole alkaloids isolated from Penicillium and Aspergillus species. Their potent insecticidal activity arises from selectively activating glutamate-gated chloride channels (GluCls) in invertebrates, not affecting human ligand-gated anion channels. Okaramines B (1) and D (2) contain a polycyclic skeleton, including an azocine ring and an unprecedented 2-dimethyl-3-methyl-azetidine ring. Owing to their complex scaffold, okaramines have inspired many total synthesis efforts, but the enzymology of the okaramine biosynthetic pathway remains unexplored. Here, we identified and characterized the biosynthetic gene cluster (oka) of 1 and 2, then elucidated the pathway with target gene inactivation, heterologous reconstitution, and biochemical characterization. Notably, we characterized an α-ketoglutarate-dependent non-heme Fe dioxygenase that forged the azetidine ring on the okaramine skeleton.
奥卡胺类是一类从青霉属和曲霉属物种中分离得到的复杂吲哚生物碱。它们具有很强的杀虫活性，这是因为它们能够选择性地激活无脊椎动物中的谷氨酸门控氯离子通道（GluCls），而不会影响人类配体门控阴离子通道。奥卡胺 B（1）和 D（2）含有一个多环骨架，包括一个氮杂环辛烷环和一个前所未有的 2,3-二甲基氮杂环丁烷环。由于其复杂的支架，奥卡胺类化合物激发了许多全合成的努力，但奥卡胺生物合成途径的酶学仍未得到探索。在这里，我们鉴定并表征了 1 和 2 的生物合成基因簇（oka），然后通过靶基因失活、异源重建和生化表征阐明了途径。值得注意的是，我们表征了一个α-酮戊二酸依赖性非血红素 Fe 双加氧酶，它在奥卡胺骨架上形成氮杂环丁烷环。
