Institute of Structural and Molecular Biology, Department of Biological Sciences, Birkbeck College, London, UK.
strucTEM Microscopic Services, Gammelsdorf, Germany.
Nature. 2022 Jul;607(7917):191-196. doi: 10.1038/s41586-022-04859-y. Epub 2022 Jun 22.
Bacterial conjugation is the fundamental process of unidirectional transfer of DNAs, often plasmid DNAs, from a donor cell to a recipient cell. It is the primary means by which antibiotic resistance genes spread among bacterial populations. In Gram-negative bacteria, conjugation is mediated by a large transport apparatus-the conjugative type IV secretion system (T4SS)-produced by the donor cell and embedded in both its outer and inner membranes. The T4SS also elaborates a long extracellular filament-the conjugative pilus-that is essential for DNA transfer. Here we present a high-resolution cryo-electron microscopy (cryo-EM) structure of a 2.8 megadalton T4SS complex composed of 92 polypeptides representing 8 of the 10 essential T4SS components involved in pilus biogenesis. We added the two remaining components to the structural model using co-evolution analysis of protein interfaces, to enable the reconstitution of the entire system including the pilus. This structure describes the exceptionally large protein-protein interaction network required to assemble the many components that constitute a T4SS and provides insights on the unique mechanism by which they elaborate pili.
细菌接合是 DNA（通常是质粒 DNA）从供体细胞单向转移到受体细胞的基本过程。它是抗生素抗性基因在细菌种群中传播的主要途径。在革兰氏阴性菌中，接合是由供体细胞产生的大型运输装置——共轭型 IV 型分泌系统（T4SS）介导的，并嵌入其外膜和内膜中。T4SS 还精心制作了一条长的细胞外细丝——共轭菌毛，这对于 DNA 转移是必不可少的。在这里，我们展示了一个 2.8 兆道尔顿 T4SS 复合物的高分辨率冷冻电镜（cryo-EM）结构，该复合物由 92 种多肽组成，代表了参与菌毛生物发生的 10 个必需 T4SS 组件中的 8 个。我们使用蛋白质界面的共进化分析将另外两个组件添加到结构模型中，从而能够重建包括菌毛在内的整个系统。该结构描述了组装构成 T4SS 的许多组件所需的异常大的蛋白质-蛋白质相互作用网络，并提供了有关它们如何精心制作菌毛的独特机制的见解。
