Department of Biomolecular Chemistry, Leibniz Institute for Natural Product Research and Infection Biology-, Hans Knöll Institute, Beutenbergstrasse 11a, 07745, Jena, Germany.
Chair for Natural Product Chemistry, Friedrich Schiller University, Jena, Germany.
Angew Chem Int Ed Engl. 2018 Aug 27;57(35):11223-11227. doi: 10.1002/anie.201804991. Epub 2018 Jul 24.
Ketosynthase (KS) domains of modular type I polyketide synthases (PKSs) typically catalyze the Claisen condensation of acyl and malonyl units to form linear chains. In stark contrast, the KS of the rhizoxin PKS branching module mediates a Michael addition, which sets the basis for a pharmacophoric δ-lactone moiety. The precise role of the KS was evaluated by site-directed mutagenesis, chemical probes, and biotransformations. Biochemical and kinetic analyses helped to dissect branching and lactonization reactions and unequivocally assign the entire sequence to the KS. Probing the range of accepted substrates with diverse synthetic surrogates in vitro, we found that the KS tolerates defined acyl chain lengths to produce five- to seven-membered lactones. These results show that the KS is multifunctional, as it catalyzes β-branching and lactonization. Information on the increased product portfolio of the unusual, TE-independent on-line cyclization is relevant for synthetic biology approaches.
酮合酶（KS）结构域的模块化类型 I 聚酮合酶（PKS）通常催化酰基和丙二酰基单元的 Claisen 缩合，形成线性链。与此形成鲜明对比的是，rhizoxin PKS 分支模块的 KS 介导迈克尔加成，这为药效团 δ-内酯部分奠定了基础。通过定点突变、化学探针和生物转化评估了 KS 的精确作用。生化和动力学分析有助于剖析分支和内酯化反应，并明确将整个序列分配给 KS。通过体外使用各种合成类似物探测接受的底物范围，我们发现 KS 可以容忍定义的酰基链长度，从而产生五至七个成员的内酯。这些结果表明 KS 具有多功能性，因为它可以催化 β-支化和内酯化。有关不寻常的、TE 独立在线环化的增加的产物组合的信息对于合成生物学方法是相关的。
