Conjugative type IV secretion systems (T4SS) mediate bacterial conjugation, a process that enables the unidirectional exchange of genetic materials between a donor and a recipient bacterial cell. Bacterial conjugation is the primary means by which antibiotic resistance genes spread among bacterial populations (Barlow 2009; Virolle et al, 2020). Conjugative T4SSs form pili: long extracellular filaments that connect with recipient cells. Previously, we solved the cryo-electron microscopy (cryo-EM) structure of a conjugative T4SS. In this article, based on additional data, we present a more complete T4SS cryo-EM structure than that published earlier. Novel structural features include details of the mismatch symmetry within the OMCC, the presence of a fourth VirB8 subunit in the asymmetric unit of both the arches and the inner membrane complex (IMC), and a hydrophobic VirB5 tip in the distal end of the stalk. Additionally, we provide previously undescribed structural insights into the protein VirB10 and identify a novel regulation mechanism of T4SS-mediated pilus biogenesis by this protein, that we believe is a key checkpoint for this process.

中文翻译：

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接合型 IV 型分泌系统的冷冻电镜结构表明存在调节菌毛生物发生的分子开关。


接合 IV 型分泌系统 (T4SS) 介导细菌接合，这一过程使得供体和受体细菌细胞之间能够单向交换遗传物质。细菌接合是抗生素抗性基因在细菌群体中传播的主要手段（Barlow 2009；Virolle 等人，2020）。接合 T4SS 形成菌毛：与受体细胞连接的长细胞外丝。此前，我们解析了共轭 T4SS 的冷冻电子显微镜 (cryo-EM) 结构。在本文中，基于额外的数据，我们提出了比之前发布的更完整的 T4SS 冷冻电镜结构。新颖的结构特征包括 OMCC 内错配对称性的细节、拱门和内膜复合体 (IMC) 的不对称单元中存在第四个 VirB8 亚基，以及茎远端的疏水性 VirB5 尖端。此外，我们提供了之前未描述的蛋白质 VirB10 的结构见解，并确定了该蛋白质 T4SS 介导的菌毛生物发生的新调节机制，我们认为这是该过程的关键检查点。