Type II polyketide synthases (PKSs) normally synthesize polycyclic aromatic compounds in nature, and the potential to elaborate further diverse skeletons was recently revealed by the discovery of a polyene subgroup. Here, we show a type II PKS machinery for the biosynthesis of a five-membered nonaromatic skeleton contained in the nonproteinogenic amino acid cispentacin and the plant toxin coronatine. We successfully produce cispentacin in a heterologous host and reconstruct its biosynthesis using seven recombinant proteins in vitro. Biochemical analyses of each protein reveal the unique enzymatic reactions, indicating that a heterodimer of type II PKS-like enzymes (AmcF–AmcG) catalyzes a single C₂ elongation as well as a subsequent cyclization on the acyl carrier protein (AmcB) to form a key intermediate with a five-membered ring. The subsequent reactions, which are catalyzed by a collection of type II PKS-like enzymes, are also peculiar. This work further expands the definition of type II PKS and illuminates an unexplored genetic resource for natural products.

II 型聚酮合酶 (PKS) 通常在自然界中合成多环芳香族化合物，最近多烯亚组的发现揭示了进一步阐述多样化骨架的潜力。在这里，我们展示了一种 II 型 PKS 机制，用于生物合成非蛋白氨基酸顺喷他星和植物毒素冠菌素中所含的五元非芳香族骨架。我们成功地在异源宿主中生产顺喷他星，并在体外使用七种重组蛋白重建其生物合成。每种蛋白质的生化分析揭示了独特的酶反应，表明 II 型 PKS 样酶 (AmcF–AmcG) 的异二聚体催化单个 C ₂延伸以及随后在酰基载体蛋白 (AmcB) 上的环化，形成具有五元环的关键中间体。随后由一系列 II 型 PKS 类酶催化的反应也很奇特。这项工作进一步扩展了 II 型 PKS 的定义，并阐明了未经开发的天然产物遗传资源。