Department of Pathology and Laboratory Medicine, University of Texas Health Science Center, Houston, TX 77030, USA.
Proc Natl Acad Sci U S A. 2013 Aug 27;110(35):14390-5. doi: 10.1073/pnas.1308306110. Epub 2013 Aug 12.
Periplasmic flagella are essential for the distinctive morphology, motility, and infectious life cycle of the Lyme disease spirochete Borrelia burgdorferi. In this study, we genetically trapped intermediates in flagellar assembly and determined the 3D structures of the intermediates to 4-nm resolution by cryoelectron tomography. We provide structural evidence that secretion of rod substrates triggers remodeling of the central channel in the flagellar secretion apparatus from a closed to an open conformation. This open channel then serves as both a gateway and a template for flagellar rod assembly. The individual proteins assemble sequentially to form a modular rod. The hook cap initiates hook assembly on completion of the rod, and the filament cap facilitates filament assembly after formation of the mature hook. Cryoelectron tomography and mutational analysis thus combine synergistically to provide a unique structural blueprint of the assembly process of this intricate molecular machine in intact cells.
周质鞭毛对于莱姆病螺旋体伯氏疏螺旋体的独特形态、运动性和传染性生命周期至关重要。在这项研究中，我们通过基因捕获技术捕获了鞭毛组装过程中的中间体，并通过冷冻电镜断层扫描将中间体的三维结构解析至 4nm 分辨率。我们提供了结构证据，表明杆状亚基的分泌会引发鞭毛分泌装置中中央通道从关闭到开放构象的重塑。这个开放通道随后既充当了鞭毛组装的入口，也充当了模板。各个蛋白依次组装形成模块化的杆状结构。钩帽在杆状结构完成后启动钩的组装，而鞭毛丝帽在成熟钩形成后促进鞭毛丝的组装。因此，冷冻电镜断层扫描和突变分析协同提供了完整细胞中这种复杂分子机器组装过程的独特结构蓝图。
