Department of Microbial Pathogenesis, Yale University School of Medicine, New Haven, CT 06536.
Microbial Sciences Institute, Yale University School of Medicine, New Haven, CT 06536.
Proc Natl Acad Sci U S A. 2019 Dec 3;116(49):24786-24795. doi: 10.1073/pnas.1916331116. Epub 2019 Nov 19.
Type III protein secretion systems are essential virulence factors for many important pathogenic bacteria. The entire protein secretion machine is composed of several substructures that organize into a holostructure or injectisome. The core component of the injectisome is the needle complex, which houses the export apparatus that serves as a gate for the passage of the secreted proteins through the bacterial inner membrane. Here, we describe a high-resolution structure of the export apparatus of the type III secretion system in association with the needle complex and the underlying bacterial membrane, both in isolation and in situ. We show the precise location of the core export apparatus components within the injectisome and bacterial envelope and demonstrate that their deployment results in major membrane remodeling and thinning, which may be central for the protein translocation process. We also show that InvA, a critical export apparatus component, forms a multiring cytoplasmic conduit that provides a pathway for the type III secretion substrates to reach the entrance of the export gate. Combined with structure-guided mutagenesis, our studies provide major insight into potential mechanisms of protein translocation and injectisome assembly.
III 型蛋白分泌系统是许多重要致病菌的重要毒力因子。整个蛋白分泌机器由几个亚结构组成，这些亚结构组织成一个整体结构或注射器。注射器的核心组件是针复合物，其中容纳着出口设备，作为分泌蛋白通过细菌内膜的通道的门。在这里，我们描述了 III 型分泌系统的出口设备与针复合物和底层细菌膜的高分辨率结构，无论是在分离状态还是原位状态下。我们展示了核心出口设备组件在注射器和细菌包膜内的精确位置，并证明它们的部署导致了主要的膜重塑和变薄，这可能是蛋白转运过程的核心。我们还表明，InvA，一个关键的出口设备组件，形成了一个多环细胞质管道，为 III 型分泌底物到达出口门入口提供了途径。结合结构导向的突变体分析，我们的研究为蛋白转运和注射器组装的潜在机制提供了主要的见解。
