Department of Pathology and Laboratory Medicine, University of Texas Medical School at Houston , Houston, Texas 77030, United States.
Biochemistry. 2014 Jul 15;53(27):4323-33. doi: 10.1021/bi500059y. Epub 2014 Jul 1.
The flagellum is one of the most sophisticated self-assembling molecular machines in bacteria. Powered by the proton-motive force, the flagellum rapidly rotates in either a clockwise or counterclockwise direction, which ultimately controls bacterial motility and behavior. Escherichia coli and Salmonella enterica have served as important model systems for extensive genetic, biochemical, and structural analysis of the flagellum, providing unparalleled insights into its structure, function, and gene regulation. Despite these advances, our understanding of flagellar assembly and rotational mechanisms remains incomplete, in part because of the limited structural information available regarding the intact rotor-stator complex and secretion apparatus. Cryo-electron tomography (cryo-ET) has become a valuable imaging technique capable of visualizing the intact flagellar motor in cells at molecular resolution. Because the resolution that can be achieved by cryo-ET with large bacteria (such as E. coli and S. enterica) is limited, analysis of small-diameter bacteria (including Borrelia burgdorferi and Campylobacter jejuni) can provide additional insights into the in situ structure of the flagellar motor and other cellular components. This review is focused on the application of cryo-ET, in combination with genetic and biophysical approaches, to the study of flagellar structures and its potential for improving the understanding of rotor-stator interactions, the rotational switching mechanism, and the secretion and assembly of flagellar components.
鞭毛是细菌中最复杂的自组装分子机器之一。在质子动力势的驱动下，鞭毛快速顺时针或逆时针旋转，最终控制细菌的运动和行为。大肠杆菌和沙门氏菌已成为鞭毛的广泛遗传、生化和结构分析的重要模式系统，为其结构、功能和基因调控提供了无与伦比的见解。尽管取得了这些进展，但鞭毛组装和旋转机制的理解仍然不完整，部分原因是关于完整的转子-定子复合物和分泌装置的结构信息有限。冷冻电子断层扫描（cryo-ET）已成为一种有价值的成像技术，能够以分子分辨率可视化细胞中完整的鞭毛马达。由于 cryo-ET 对大型细菌（如大肠杆菌和沙门氏菌）的分辨率有限，因此对小直径细菌（包括伯氏疏螺旋体和空肠弯曲菌）的分析可以提供更多关于鞭毛马达和其他细胞成分的原位结构的见解。本综述重点介绍了 cryo-ET 与遗传和生物物理方法相结合在鞭毛结构研究中的应用，以及其在改善对转子-定子相互作用、旋转切换机制以及鞭毛组件的分泌和组装的理解方面的潜力。
