Department of Pathology and Laboratory Medicine, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, TX 77030.
Department of Microbial Pathogenesis, Microbial Sciences Institute, Yale School of Medicine, New Haven, CT 06536.
Proc Natl Acad Sci U S A. 2017 Oct 10;114(41):10966-10971. doi: 10.1073/pnas.1712489114. Epub 2017 Sep 25.
species are Gram-negative rod-shaped bacteria that are ubiquitous and often highly motile in aqueous environments. swimming motility is driven by a polar flagellum covered with a membranous sheath, but this sheathed flagellum is not well understood at the molecular level because of limited structural information. Here, we use as a model system to study the sheathed flagellum in intact cells by combining cryoelectron tomography (cryo-ET) and subtomogram analysis with a genetic approach. We reveal striking differences between sheathed and unsheathed flagella in cells, including a novel ring-like structure at the bottom of the hook that is associated with major remodeling of the outer membrane and sheath formation. Using mutants defective in flagellar motor components, we defined a specific feature (also known as the T ring) as a distinctive periplasmic structure with 13-fold symmetry. The unique architecture of the T ring provides a static platform to recruit the PomA/B complexes, which are required to generate higher torques for rotation of the sheathed flagellum and fast motility of cells. Furthermore, the flagellar motor exhibits an intrinsic length variation between the inner and the outer membrane bound complexes, suggesting the outer membrane bound complex can shift slightly along the axial rod during flagellar rotation. Together, our detailed analyses of the polar flagella in intact cells provide insights into unique aspects of the sheathed flagellum and the distinct motility of species.
这些物种是革兰氏阴性杆状细菌，在水相环境中普遍存在且通常具有高度的运动性。游动运动是由覆盖有膜鞘的极性鞭毛驱动的，但由于结构信息有限，这种有鞘鞭毛在分子水平上还没有得到很好的理解。在这里，我们使用 作为模型系统，通过结合冷冻电子断层扫描（cryo-ET）和亚断层分析以及遗传方法，在完整细胞中研究有鞘鞭毛。我们揭示了 细胞中鞘鞭毛和无鞘鞭毛之间的显著差异，包括钩的底部存在一种新颖的环状结构，与外膜和鞘形成的主要重塑有关。使用鞭毛马达成分缺陷的突变体，我们将一个特定的特征（也称为 T 环）定义为一种具有 13 重对称性的独特周质结构。T 环的独特结构为招募 PomA/B 复合物提供了一个静态平台，这对于产生有鞘鞭毛的旋转和 细胞的快速运动所需的更高扭矩是必需的。此外，鞭毛马达在内外膜结合复合物之间表现出固有长度变化，这表明外膜结合复合物在鞭毛旋转过程中可以沿轴向杆略微移动。总之，我们对完整细胞中极性鞭毛的详细分析提供了对有鞘鞭毛和 物种独特运动性的独特方面的深入了解。
