State Key Laboratory of Pharmaceutical Biotechnology, Institute of Functional Biomolecules, Chemistry and Biomedicine Innovation Center (ChemBIC), School of Life Sciences, Nanjing University, Nanjing 210023, China.
State Key Laboratory of Analytical Chemistry for Life Science, Jiangsu Key Laboratory of Advanced Organic Materials, Chemistry and Biomedicine Innovation Center (ChemBIC), School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
J Am Chem Soc. 2022 May 4;144(17):7939-7948. doi: 10.1021/jacs.2c02855. Epub 2022 Apr 26.
Cinnamoyl-containing natural products (CCNPs) are a small class of bacterial metabolites with notable bioactivities. The biosynthesis of cinnamoyl moiety has been proposed to be assembled by an unusual highly reducing (HR) type II polyketide synthases (PKS). However, the biosynthetic route, especially the cyclization step for the benzene ring formation, remains unclear. In this work, we successfully reconstituted the pathway of cinnamoyl moiety in kitacinnamycin biosynthesis through a step-wise approach and demonstrated that a three-protein complex, Kcn17-Kcn18-Kcn19, can catalyze 6π-electrocyclization followed by dehydrogenation to form the benzene ring. We found that the three-protein homologues were widely distributed among 207 HR type II PKS biosynthetic gene clusters including five known CCNPs. In contrast, in the biosynthesis of youssoufene, a cinnamoyl-containing polyene, we identified that the benzene ring formation was accomplished by a distinct orphan protein. Thus, our work resolved the long-standing mystery in cinnamoyl biosynthesis and revealed two distinct enzymes that can synthesize benzene rings polyene precursors.
含肉桂酰基的天然产物（CCNPs）是一类具有显著生物活性的细菌代谢产物。肉桂酰部分的生物合成被认为是由一种不寻常的高还原（HR）型 II 聚酮合酶（PKS）组装而成。然而，生物合成途径，特别是苯环形成的环化步骤，仍然不清楚。在这项工作中，我们通过逐步方法成功重建了 kitacinnamycin 生物合成中肉桂酰部分的途径，并证明了一个由三个蛋白组成的复合物 Kcn17-Kcn18-Kcn19 可以催化 6π-电环化，然后脱氢形成苯环。我们发现这三个蛋白同源物广泛分布在包括五个已知 CCNPs 的 207 个 HR 型 II PKS 生物合成基因簇中。相比之下，在肉桂酰基多烯 youssoufene 的生物合成中，我们发现苯环的形成是由一个独特的孤儿蛋白完成的。因此，我们的工作解决了肉桂酰生物合成中长期存在的谜团，并揭示了两种可以合成苯环的不同酶类 多烯前体。
