Secretion systems are employed by bacteria to transport macromolecules across membranes without compromising their integrities. Processes including virulence, colonization, and motility are highly dependent on the secretion of effector molecules toward the immediate cellular environment, and in some cases, into the host cytoplasm. In Type II and Type III secretion systems, as well as in Type IV pili, homomultimeric complexes known as secretins form large pores in the outer bacterial membrane, and the localization and assembly of such 1 MDa molecules often relies on pilotins or accessory proteins. Significant progress has been made toward understanding details of interactions between secretins and their partner proteins using approaches ranging from bacterial genetics to cryo electron microscopy. This review provides an overview of the mode of action of pilotins and accessory proteins for T2SS, T3SS, and T4PS secretins, highlighting recent near-atomic resolution cryo-EM secretin complex structures and underlining the importance of these interactions for secretin functionality.

中文翻译：

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细菌促胰液素：组装和膜靶向的机制。

细菌利用分泌系统在膜上转运大分子而不损害其完整性。包括毒性，定植和运动性在内的过程高度依赖于效应分子向直接细胞环境的分泌，在某些情况下还向宿主细胞质的分泌。在II型和III型分泌系统以及IV型菌毛中，称为促泌素的同源多聚体复合物在细菌外膜上形成大孔，而这种1 MDa分子的定位和组装通常依赖于前导蛋白或辅助蛋白。在从细菌遗传学到冷冻电子显微镜的各种方法中，在了解促泌素及其伴侣蛋白之间相互作用的细节方面取得了重大进展。