The non-benzenoid aromatic tropone ring is a structural motif of numerous microbial and plant natural products with potent bioactivities. In bacteria, tropone biosynthesis involves early steps of the widespread CoA-dependent phenylacetic acid (paa) catabolon, from which a shunt product is sequestered and surprisingly further utilized as a universal precursor for structurally and functionally diverse tropone derivatives such as tropodithietic acid or (hydroxy)tropolones. Here, we elucidate the biosynthesis of the antibiotic 3,7-dihydroxytropolone in Actinobacteria by in vitro pathway reconstitution using paa catabolic enzymes as well as dedicated downstream tailoring enzymes, including a thioesterase (TrlF) and two flavoprotein monooxygenases (TrlCD and TrlE). We furthermore mechanistically and structurally characterize the multifunctional key enzyme TrlE, which mediates an unanticipated ipso-substitution involving a hydroxylation and subsequent decarboxylation of the CoA-freed side chain, followed by ring oxidation to afford tropolone. This study showcases a remarkably efficient strategy for 3,7-dihydroxytropolone biosynthesis and illuminates the functions of the involved biosynthetic enzymes.

中文翻译：

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通过酶法回收分解代谢分流产物生物合成细菌抗生素 3,7-二羟基托酚酮

非苯环芳香环酮环是许多具有有效生物活性的微生物和植物天然产物的结构基序。在细菌中，托品酮生物合成涉及广泛的 CoA 依赖性苯乙酸 (paa) 分解代谢物的早期步骤，其中分流产物被隔离，并令人惊讶地进一步用作结构和功能多样的托品酮衍生物的通用前体，例如原二硫酸或（羟基） ）托酚酮。在这里，我们通过使用 paa 分解代谢酶以及专用下游定制酶（包括硫酯酶 (TrlF) 和两种黄素蛋白单加氧酶（TrlCD 和 TrlE））体外途径重建，阐明了放线菌中抗生素 3,7-二羟基托酚酮的生物合成。我们还从机制和结构上表征了多功能关键酶 TrlE，它介导意料之外的原位取代，涉及羟基化和随后的不含 CoA 的侧链脱羧，然后进行环氧化以提供托酚酮。这项研究展示了一种非常有效的 3,7-二羟基托酚酮生物合成策略，并阐明了所涉及的生物合成酶的功能。