Polyketides are a large class of bioactive natural products with a wide range of structures and functions. Polyketides are biosynthesized by large, multidomain enzyme complexes termed polyketide synthases (PKSs). One of the primary challenges when studying PKSs is the high reactivity of their poly-β-ketone substrates. This has hampered structural and mechanistic characterization of PKS-polyketide complexes, and, as a result, little is known about how PKSs position the unstable substrates for proper catalysis while displaying high levels of regio- and stereospecificity. As a first step toward a general plan to use oxetanes as carbonyl isosteres to broadly interrogate PKS chemistry, we describe the development and application of an oxetane-based PKS substrate mimic. This enabled the first structural determination of the acyl-enzyme intermediate of a ketosynthase (KS) in complex with an inert extender unit mimic. The crystal structure, in combination with molecular dynamics simulations, led to a proposed mechanism for the unique activity of DpsC, the priming ketosynthase for daunorubicin biosynthesis. The successful application of an oxetane-based polyketide mimic suggests that this novel class of probes could have wide-ranging applications to the greater biosynthetic community interested in the mechanistic enzymology of iterative PKSs.

中文翻译：

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基于氧杂环丁烷的聚酮化合物替代物探测聚酮化合物合酶中的底物结合

聚酮化合物是一大类具有广泛结构和功能的生物活性天然产物。聚酮化合物由称为聚酮化合物合酶 (PKS) 的大型多域酶复合物生物合成。研究 PKS 时的主要挑战之一是其聚β-酮底物的高反应性。这阻碍了 PKS-聚酮化合物复合物的结构和机械表征，因此，关于 PKS 如何定位不稳定的底物以进行适当的催化，同时显示出高水平的区域和立体特异性，知之甚少。作为使用氧杂环丁烷作为羰基等排体来广泛询问 PKS 化学的总体计划的第一步，我们描述了基于氧杂环丁烷的 PKS 底物模拟物的开发和应用。这使得首次对与惰性扩展单元模拟物复合的酮合酶 (KS) 的酰基酶中间体进行结构测定。晶体结构与分子动力学模拟相结合，导致了 DpsC 独特活性的拟议机制，DpsC 是柔红霉素生物合成的引发酮合酶。基于氧杂环丁烷的聚酮化合物模拟物的成功应用表明，这类新型探针可以广泛应用于对迭代 PKS 的机械酶学感兴趣的更大的生物合成社区。