Legionella pneumophila is an opportunistic pathogen that causes the potentially fatal pneumonia known as Legionnaires' Disease. The pathology associated with infection depends on bacterial delivery of effector proteins into the host via the membrane spanning Dot/Icm type IV secretion system (T4SS). We have determined sub-3.0 Å resolution maps of the Dot/Icm T4SS core complex by single particle cryo-EM. The high-resolution structural analysis has allowed us to identify proteins encoded outside the Dot/Icm genetic locus that contribute to the core T4SS structure. We can also now define two distinct areas of symmetry mismatch, one that connects the C18 periplasmic ring (PR) and the C13 outer membrane cap (OMC) and one that connects the C13 OMC with a 16-fold symmetric dome. Unexpectedly the connection between the PR and OMC is DotH, with five copies sandwiched between the OMC and PR to accommodate the symmetry mismatch. Finally, we observe multiple conformations in the reconstructions that indicate flexibility within the structure.

中文翻译：

---

冷冻电镜揭示了嗜肺军团菌 Dot/Icm T4SS 中新的物种特异性蛋白质和对称元件


嗜肺军团菌是一种机会性病原体，可引起潜在致命的肺炎，称为军团病。与感染相关的病理学取决于细菌通过跨膜 Dot/Icm IV 型分泌系统 (T4SS) 将效应蛋白传递到宿主中。我们通过单粒子冷冻电镜确定了 Dot/Icm T4SS 核心复合物的亚 3.0 Å 分辨率图。高分辨率结构分析使我们能够识别 Dot/Icm 基因位点之外编码的蛋白质，这些蛋白质有助于核心 T4SS 结构。我们现在还可以定义两个不同的对称失配区域，一个连接 C18 周质环 (PR) 和 C13 外膜帽 (OMC)，另一个连接 C13 OMC 与 16 折对称圆顶。出乎意料的是，PR 和 OMC 之间的连接是 DotH，OMC 和 PR 之间夹有五个副本，以适应对称性不匹配。最后，我们在重建中观察到多种构象，表明结构内的灵活性。