Tseytin Irit, Mitrovic Bosko, David Nofar, Langenfeld Katja, Zarivach Raz, Diepold Andreas, Sal-Man Neta
The Shraga Segal Department of Microbiology, Immunology and Genetics, Faculty of Health Sciences, Ben-Gurion University of the Negev, Be'er Sheva, Israel.
Department of Ecophysiology, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany.
Front Microbiol. 2019 Nov 13;10:2551. doi: 10.3389/fmicb.2019.02551. eCollection 2019.
Many gram-negative pathogens utilize a protein complex, termed the type III secretion system (T3SS), to inject virulence factors from their cytoplasm directly into the host cell. An export apparatus that is formed by five putative integral membrane proteins (SctR/S/T/U/V), resides at the center of the T3SS complex. In this study, we characterized the smallest export apparatus protein, SctS, which contains two putative transmembrane domains (PTMD) that dynamically extract from the inner membrane and adopt a helix-turn-helix structure upon assembly of the T3SS. Replacement of each SctS PTMD with an alternative hydrophobic sequence resulted in abolishment of the T3SS activity, yet SctS self- and hetero-interactions as well as the overall assembly of the T3SS complex were unaffected. Our findings suggest that SctS PTMDs are not crucial for the interactions or the assembly of the T3SS base complex but rather that they are involved in adjusting the orientation of the export apparatus relative to additional T3SS sub-structures, such as the cytoplasmic- and the inner-membrane rings. This ensures the fittings between the dynamic and static components of the T3SS and supports the functionality of the T3SS complex.
许多革兰氏阴性病原体利用一种称为III型分泌系统（T3SS）的蛋白质复合物，将其细胞质中的毒力因子直接注入宿主细胞。由五种假定的整合膜蛋白（SctR/S/T/U/V）形成的输出装置位于T3SS复合物的中心。在本研究中，我们对最小的输出装置蛋白SctS进行了表征，它包含两个假定的跨膜结构域（PTMD），这些结构域动态地从内膜中提取出来，并在T3SS组装时形成螺旋-转角-螺旋结构。用替代的疏水序列替换每个SctS PTMD会导致T3SS活性丧失，但SctS的自我和异源相互作用以及T3SS复合物的整体组装不受影响。我们的研究结果表明，SctS PTMD对T3SS基础复合物的相互作用或组装并不关键，而是参与调整输出装置相对于其他T3SS子结构（如细胞质环和内膜环）的方向。这确保了T3SS动态和静态组件之间的适配，并支持T3SS复合物的功能。
