Maiti Shyantani, Mitra Pralay
Department of Computer Science and Engineering, Indian Institute of Technology, Kharagpur, West Bengal, 721302, India.
J Mol Model. 2018 Sep 13;24(10):280. doi: 10.1007/s00894-018-3819-0.
Flagellar rotation regulates the phenomenon of chemotaxis in bacteria. The interaction between the stator unit and the rotor unit of the flagellar motors is responsible for switching the direction of bacterial flagellar rotation. However, the molecular interaction mechanism between the stator (MotA/MotB) and the rotor (FliG/FliM/FliN) proteins for the flagellar rotational direction switching was not very clear. To address this, the asymmetry in the copies of FliG, FliM, and FliN molecules was resolved by reconstructing the switch complex using a modeled rotor unit that fulfills the experimentally available geometric constraints. The diameter of our assembled switch complex supported the existing literature. Experimental evidence and the conformational spread model validates our constructed switch complex. Subsequently, normal mode analysis (NMA) on these constructed protomer units revealed that the most fluctuating molecule in the rotor unit is FliG, which interacts with the bacterial stator through its C-terminal domain. NMA also facilitates our understanding of the reorientation mechanism of FliG between the two states of its flagellar rotation, i.e., counter-clockwise to clockwise and vice versa. Our observations regarding speed regulation, the gap between rotor and stator, and the flagellar switching due to the activity of cytoplasmic proteins, indicate that the bacterial flagellar motor uses the same mechanism as that of an electric motor. Graphical abstract Molecular mechanism of the bacterial flagellar switch.
鞭毛旋转调节细菌中的趋化现象。鞭毛马达的定子单元和转子单元之间的相互作用负责切换细菌鞭毛旋转的方向。然而，定子（MotA/MotB）和转子（FliG/FliM/FliN）蛋白之间用于鞭毛旋转方向切换的分子相互作用机制尚不清楚。为了解决这个问题，通过使用满足实验可用几何约束的建模转子单元重建开关复合体，解决了FliG、FliM和FliN分子拷贝中的不对称性。我们组装的开关复合体的直径支持现有文献。实验证据和构象扩展模型验证了我们构建的开关复合体。随后，对这些构建的原体单元进行的正常模式分析（NMA）表明，转子单元中波动最大的分子是FliG，它通过其C端结构域与细菌定子相互作用。NMA还有助于我们理解FliG在其鞭毛旋转的两种状态之间重新定向的机制，即逆时针到顺时针，反之亦然。我们关于速度调节、转子与定子之间的间隙以及由于细胞质蛋白活性导致的鞭毛切换的观察结果表明，细菌鞭毛马达使用与电动机相同的机制。图形摘要 细菌鞭毛开关的分子机制。
