Modular polyketide synthases (PKSs) produce numerous structurally complex natural products that have diverse applications in medicine and agriculture. PKSs typically consist of several multienzyme subunits that utilize structurally defined docking domains (DDs) at their N and C termini to ensure correct assembly into functional multiprotein complexes. Here we report a fundamentally different mechanism for subunit assembly in trans-acyltransferase (trans-AT) modular PKSs at the junction between ketosynthase (KS) and dehydratase (DH) domains. This mechanism involves direct interaction of a largely unstructured docking domain (DD) at the C terminus of the KS with the surface of the downstream DH. Acyl transfer assays and mechanism-based crosslinking established that the DD is required for the KS to communicate with the acyl carrier protein appended to the DH. Two distinct regions for binding of the DD to the DH were identified using NMR spectroscopy, carbene footprinting, and mutagenesis, providing a foundation for future elucidation of the molecular basis for interaction specificity.

模块化聚酮化合物合酶（PKS）产生许多结构复杂的天然产物，这些产物在医学和农业中具有多种应用。PKS通常由几个多酶亚基组成，这些亚酶在其N和C末端利用结构定义的对接域（DD），以确保正确组装成功能性多蛋白复合物。在这里，我们报告了在反式酰基转移酶（反式-AT）酮合成酶（KS）和脱水酶（DH）域之间的连接处的模块化PKS。此机制涉及在KS的C末端的很大程度上非结构化的对接结构域（DD）与下游DH的表面直接相互作用。酰基转移分析和基于机理的交联确定了DD与DH附加的酰基载体蛋白进行通讯时DD是必需的。使用NMR光谱，卡宾足迹和诱变鉴定了DD与DH结合的两个不同区域，为将来阐明相互作用特异性的分子基础提供了基础。