Structure of a modular polyketide synthase

摘要

Polyketide natural products constitute a broad class of compounds with diverse structural features and biological activities. Their biosynthetic machinery, represented by type I polyketide synthases (PKSs), has an architecture in which successive modules catalyse two-carbon linear extensions and keto-group processing reactions on intermediates covalently tethered to carrier domains. Here we used electron cryo-microscopy to determine sub-nanometre-resolution three-dimensional reconstructions of a full-length PKS module from the bacterium Streptomyces venezuelae that revealed an unexpectedly different architecture compared to the homologous dimeric mammalian fatty acid synthase. A single reaction chamber provides access to all catalytic sites for the intramodule carrier domain. In contrast, the carrier from the preceding module uses a separate entrance outside the reaction chamber to deliver the upstream polyketide intermediate for subsequent extension and modification. This study reveals for the first time, to our knowledge, the structural basis for both intramodule and intermodule substrate transfer in polyketide synthases, and establishes a new model for molecular dissection of these multifunctional enzyme systems.%聚酮合酶(PKSs)是生成聚酮（一大类次级代谢产物——换句话说就是天然产物）的多域酶复合物。来自Georgios Skiniotis及同事的两篇论文用低温电子显微镜来研究"委内瑞拉链霉菌"的苦霉素生物合成中所涉及的一个完好无损的全长度多酶PKS模块在不同功能状态下的结构。这些结构显示，酮基合酶、酰基转移酶、酮还原酶和酰基载体蛋白（ACP)域在催化周期中相互作用。在每一种状态，ACP处于不同位置，来促进中间体向下一个催化步骤和下一个模块转移。