Department of Biomolecular Chemistry, Leibniz Institute for Natural Product Research and Infection Biology (HKI), Beutenbergstr. 11a, 07745 Jena, Germany.
Center for Integrated Protein Science Munich (CIPSM), Department Chemie, Technische Universität München, Lichtenbergstr. 4, 85748 Garching, Germany.
Nat Commun. 2017 Jun 15;8:15804. doi: 10.1038/ncomms15804.
Terpenoid natural products comprise a wide range of molecular architectures that typically result from C-C bond formations catalysed by classical type I/II terpene cyclases. However, the molecular diversity of biologically active terpenoids is substantially increased by fully unrelated, non-canonical terpenoid cyclases. Their evolutionary origin has remained enigmatic. Here we report the in vitro reconstitution of an unusual flavin-dependent bacterial indoloterpenoid cyclase, XiaF, together with a designated flavoenzyme-reductase (XiaP) that mediates a key step in xiamycin biosynthesis. The crystal structure of XiaF with bound FADH (at 2.4 Å resolution) and phylogenetic analyses reveal that XiaF is, surprisingly, most closely related to xenobiotic-degrading enzymes. Biotransformation assays show that XiaF is a designated indole hydroxylase that can be used for the production of indigo and indirubin. We unveil a cryptic hydroxylation step that sets the basis for terpenoid cyclization and suggest that the cyclase has evolved from xenobiotics detoxification enzymes.
萜类天然产物包含广泛的分子结构，这些结构通常是由经典的 I/II 型萜烯环化酶催化的 C-C 键形成产生的。然而，完全不相关的非典型萜烯环化酶大大增加了具有生物活性的萜类化合物的分子多样性。它们的进化起源仍然是个谜。在这里，我们报告了一种不寻常的黄素依赖型细菌吲哚萜烯环化酶 XiaF 的体外重建，以及一种在小霉素生物合成中介导关键步骤的指定黄素酶还原酶 (XiaP)。XiaF 与结合的 FADH 的晶体结构（分辨率为 2.4 Å）和系统发育分析表明，令人惊讶的是，XiaF 与外来物质降解酶最密切相关。生物转化实验表明，XiaF 是一种指定的吲哚羟化酶，可用于靛蓝和靛玉红的生产。我们揭示了萜烯环化的基础上的一个隐匿的羟化步骤，并表明该环化酶是从外来物质解毒酶进化而来的。
