Structural bases for F plasmid conjugation and F pilus biogenesis in Escherichia coli
Structural bases for F plasmid conjugation and F pilus biogenesis in Escherichia coli
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DOI：
10.1073/pnas.1904428116
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发表时间：
2019-07-09
影响因子：
11.1
通讯作者：
Christie, Peter J.
中科院分区：
文献类型：
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作者：
Hu, Bo;Khara, Pratick;Christie, Peter J.
细菌接合系统是IV型分泌系统（T4 SS）超家族的成员。20世纪40年代首次报道了肠杆菌科中F质粒的接合转移，但F质粒编码的转移通道的结构及其与F菌毛的物理关系仍然未知。我们通过原位冷冻电子断层扫描（CryoET）可视化了天然细菌细胞包膜中的F编码结构。值得注意的是，F质粒编码四种不同的结构，而不仅仅是普遍模型预测的易位通道或通道-菌毛复合物。F1结构由不同的外膜复合物和内膜复合物以及连接圆柱体组成，它们共同容纳跨膜转运通道。F2结构基本上是F1复合体，F菌毛附着在外膜（OM）上。值得注意的是，F3结构由附着于薄的、跨越细胞壁的柄的F菌毛组成，而F4结构由停靠于OM的菌毛组成，而没有相关的周质密度。交通ATP酶TraC被配置为在F1和F2结构的细胞质面处的二聚体的六聚体，在那里它分别调节底物转移和F菌毛生物发生。总之，我们的研究结果提出了建筑渲染的DNA共轭或“交配”通道，通道菌毛连接，和前所未有的菌毛基础结构。这些结构快照支持F转移系统的生物起源模型，并允许与其他结构特征的T4 SS进行详细比较。
Bacterial conjugation systems are members of the large type IV secretion system (T4SS) superfamily. Conjugative transfer of F plasmids residing in the Enterobacteriaceae was first reported in the 1940s, yet the architecture of F plasmid-encoded transfer channel and its physical relationship with the F pilus remain unknown. We visualized F-encoded structures in the native bacterial cell envelope by in situ cryoelectron tomography (CryoET). Remarkably, F plasmids encode four distinct structures, not just the translocation channel or channel-pilus complex predicted by prevailing models. The F1 structure is composed of distinct outer and inner membrane complexes and a connecting cylinder that together house the envelope-spanning translocation channel. The F2 structure is essentially the F1 complex with the F pilus attached at the outer membrane (OM). Remarkably, the F3 structure consists of the F pilus attached to a thin, cell envelope-spanning stalk, whereas the F4 structure consists of the pilus docked to the OM without an associated periplasmic density. The traffic ATPase TraC is configured as a hexamer of dimers at the cytoplasmic faces of the F1 and F2 structures, where it respectively regulates substrate transfer and F pilus biogenesis. Together, our findings present architectural renderings of the DNA conjugation or "mating" channel, the channel-pilus connection, and unprecedented pilus basal structures. These structural snapshots support a model for biogenesis of the F transfer system and allow for detailed comparisons with other structurally characterized T4SSs.