The type II secretion system (T2SS) is a multi‐protein complex used by many bacteria to move substrates across their cell membrane. Substrates released into the environment serve as local and long‐range effectors that promote nutrient acquisition, biofilm formation, and pathogenicity. In both animals and plants, the T2SS is increasingly recognized as a key driver of virulence. The T2SS spans the bacterial cell envelope and extrudes substrates through an outer membrane secretin channel using a pseudopilus. An inner membrane assembly platform and a cytoplasmic motor controls pseudopilus assembly. This microreview focuses on the structure and mechanism of the T2SS. Advances in cryo‐electron microscopy are enabling increasingly elaborate sub‐complexes to be resolved. However, key questions remain regarding the mechanism of pseudopilus extension and retraction, and how this is coupled with the choreography of the substrate moving through the secretion system. The T2SS is part of an ancient type IV filament superfamily that may have been present within the last universal common ancestor (LUCA). Overall, mechanistic principles that underlie T2SS function have implication for other closely related systems such as the type IV and tight adherence pilus systems.

中文翻译：

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II型细菌分泌系统的结构和机制

II 型分泌系统 (T2SS) 是一种多蛋白复合物，许多细菌使用它来移动底物穿过细胞膜。释放到环境中的底物作为局部和远程效应器，促进营养获取、生物膜形成和致病性。在动物和植物中，T2SS 越来越被认为是毒力的关键驱动因素。T2SS 跨越细菌细胞包膜，并使用假菌毛通过外膜分泌素通道挤出底物。内膜组装平台和细胞质马达控制假菌毛组装。这篇微观评论侧重于 T2SS 的结构和机制。冷冻电子显微镜的进步使越来越复杂的子复合体得以解决。然而，关键问题仍然是假菌毛伸展和收缩的机制，以及它如何与通过分泌系统移动的基质的编排相结合。T2SS 是古老的 IV 型细丝超家族的一部分，该超家族可能存在于最后一个普遍共同祖先 (LUCA) 中。总体而言，作为 T2SS 功能基础的机械原理对其他密切相关的系统有影响，例如 IV 型和紧密粘附菌毛系统。