The John Innes Centre, Department of Biological Chemistry, Norwich Research Park, Norwich, UK.
Department of Biology, University of York, York, UK.
Nat Chem Biol. 2019 Jan;15(1):71-79. doi: 10.1038/s41589-018-0185-2. Epub 2018 Dec 10.
Terpene synthases typically form complex molecular scaffolds by concerted activation and cyclization of linear starting materials in a single enzyme active site. Here we show that iridoid synthase, an atypical reductive terpene synthase, catalyzes the activation of its substrate 8-oxogeranial into a reactive enol intermediate, but does not catalyze the subsequent cyclization into nepetalactol. This discovery led us to identify a class of nepetalactol-related short-chain dehydrogenase enzymes (NEPS) from catmint (Nepeta mussinii) that capture this reactive intermediate and catalyze the stereoselective cyclisation into distinct nepetalactol stereoisomers. Subsequent oxidation of nepetalactols by NEPS1 provides nepetalactones, metabolites that are well known for both insect-repellent activity and euphoric effects in cats. Structural characterization of the NEPS3 cyclase reveals that it binds to NAD yet does not utilize it chemically for a non-oxidoreductive formal [4 + 2] cyclization. These discoveries will complement metabolic reconstructions of iridoid and monoterpene indole alkaloid biosynthesis.
萜烯合酶通常通过在单个酶活性位点中协同激活和环化线性起始物来形成复杂的分子支架。在这里，我们表明，裂环烯醚萜合酶是一种非典型的还原萜烯合酶，可催化其底物 8-氧代金合欢醛活化成反应性烯醇中间物，但不催化随后的环化生成新薄荷醇。这一发现促使我们从猫薄荷（Nepeta mussinii）中鉴定出一类与新薄荷醇相关的短链脱氢酶（NEPS），它们捕获这个活性中间物，并催化立体选择性环化生成独特的新薄荷醇立体异构体。随后，NEPS1 将新薄荷醇氧化为新薄荷内酯，这些代谢物以驱虫活性和猫的欣快作用而闻名。NEPS3 环化酶的结构特征表明，它结合 NAD 但不利用其进行非氧化还原形式的 [4+2] 环化。这些发现将补充裂环烯醚萜和单萜吲哚生物碱生物合成的代谢重建。
