Type IV pili (T4P) are important virulence factors involved in host attachment and other aspects of bacterial pathogenesis. In Gram-negative bacteria, the T4P filament is polymerized from pilin subunits at the platform complex in the inner membrane (IM) and exits the outer membrane (OM) through the OM secretin channel. Although essential for T4P assembly and function, the OM secretin complexes can potentially impair the permeability barrier function of the OM and allow the entry of antibiotics and other toxic molecules. The mechanism by which Gram-negative bacteria prevent secretin-mediated OM leakage is currently not well understood. Here, we report a discovery of SlkA and SlkB (PA5122 and PA5123) that prevent permeation of several classes of antibiotics through the secretin channel of Pseudomonas aeruginosa type IV pili. We found these periplasmic proteins interact with the OM secretin complex and prevent toxic molecules from entering through the channel when there is a problem in the assembly of the T4P IM subcomplexes or when docking between the OM and IM complexes is defective. Thus, our results indicate that the secretin channel-interacting proteins play an important role in maintaining the OM permeability barrier, suggesting they may be attractive targets for potentiators that sensitize Gram-negative pathogens to antibiotics that are normally ineffective at penetrating the OM.

中文翻译：

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在铜绿假单胞菌的 IV 型菌毛组装过程中，促胰液素通道相互作用物防止抗生素流入

IV 型菌毛 (T4P) 是重要的毒力因子，涉及宿主附着和细菌发病机制的其他方面。在革兰氏阴性细菌中，T4P 细丝由内膜 (IM) 平台复合体处的菌毛蛋白亚基聚合而成，并通过 OM 分泌素通道离开外膜 (OM)。尽管对 T4P 的组装和功能至关重要，但 OM 促胰液素复合物可能会损害 OM 的渗透屏障功能，并允许抗生素和其他有毒分子进入。革兰氏阴性菌阻止促胰液素介导的 OM 泄漏的机制目前尚不清楚。在这里，我们报告了 SlkA 和 SlkB（PA5122 和 PA5123）的发现，它们阻止了几类抗生素通过铜绿假单胞菌的促胰液素通道渗透IV型菌毛。我们发现，当 T4P IM 亚复合物的组装出现问题或 OM 和 IM 复合物之间的对接有缺陷时，这些周质蛋白与 OM 分泌素复合物相互作用并阻止有毒分子通过通道进入。因此，我们的结果表明，促胰液素通道相互作用蛋白在维持 OM 通透性屏障方面发挥着重要作用，这表明它们可能是增强剂的有吸引力的目标，这些增效剂使革兰氏阴性病原体对抗生素敏感，而抗生素通常无法穿透 OM。