The bacterial type VI secretion system (T6SS) is a macromolecular machine that injects effectors into prokaryotic and eukaryotic cells. The mode of action of the T6SS is similar to contractile phages: the contraction of a sheath structure pushes a tube topped by a spike into target cells. Effectors are loaded onto the spike or confined into the tube. In enteroaggregative Escherichia coli , the Tle1 phospholipase binds the C‐terminal extension of the VgrG trimeric spike. Here, we purify the VgrG–Tle1 complex and show that a VgrG trimer binds three Tle1 monomers and inhibits their activity. Using covalent cross‐linking coupled to high‐resolution mass spectrometry, we provide information on the sites of contact and further identify the requirement for a Tle1 N‐terminal secretion sequence in complex formation. Finally, we report the 2.6‐Å‐resolution cryo‐electron microscopy tri‐dimensional structure of the (VgrG)₃–(Tle1)₃ complex revealing how the effector binds its cargo, and how VgrG inhibits Tle1 phospholipase activity. The inhibition of Tle1 phospholipase activity once bound to VgrG suggests that Tle1 dissociation from VgrG is required upon delivery.

中文翻译：

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VgrG 尖峰加载和抑制细菌 T6SS 磷脂酶效应子的结构基础。


VI型细菌分泌系统（T6SS）是一种将效应物注入原核和真核细胞的大分子机器。 T6SS 的作用模式类似于收缩噬菌体：鞘结构的收缩将顶部有刺突的管推入靶细胞。效应器安装在钉上或限制在管内。在肠聚集性大肠杆菌中，Tle1 磷脂酶结合 VgrG 三聚体刺突的 C 末端延伸。在这里，我们纯化了 VgrG-Tle1 复合物，并表明 VgrG 三聚体结合三个 Tle1 单体并抑制它们的活性。使用共价交联与高分辨率质谱联用，我们提供了接触位点的信息，并进一步确定了复合物形成中 Tle1 N 末端分泌序列的需求。最后，我们报告了 (VgrG) ₃ -(Tle1) ₃复合物的 2.6 Å 分辨率冷冻电子显微镜三维结构，揭示了效应器如何结合其货物，以及 VgrG 如何抑制 Tle1 磷脂酶活性。一旦与 VgrG 结合，Tle1 磷脂酶活性就会受到抑制，这表明 Tle1 在递送时需要从 VgrG 解离。