细菌鞭毛马达的细胞质环(C环)控制马达旋转方向,从而控制细菌的运行和翻滚行为。已显示C环响应于运动方向偏差的变化而经历自适应重塑。然而,由于荧光研究和低温电子显微镜(cryo-EM)结构分析的结果之间存在矛盾,因此C环的化学计量和排列仍不清楚。这里,通过使用C环中FliG分子的拷贝数(34)作为参考,我们精确测量了仅逆时针(CCW)和顺时针(CW)旋转的电机中FliM分子的拷贝数。我们惊讶地发现,在CW和CCW旋转电机中平均有45和58个FliM分子,分别,远远高于以前的估计。我们的结果提出了一种新的C环适应机制,也就是说,额外的FliM分子可能与初级C环结合,可能性取决于电机旋转方向。我们进一步证实,C环中的所有FliM分子在趋化性信号转导中起作用,因为它们都可以被趋化反应调节因子CheY-P结合。我们的测量为鞭毛开关的结构和布置提供了新的见解。重要性细菌鞭毛开关可根据运动旋转方向的变化进行适应性重塑,从而改变其操作点以匹配趋化信号通路的输出。然而,目前尚不清楚鞭毛开关是如何实现这种适应性重塑的.这里,通过精确的荧光研究,我们测量了逆时针和顺时针旋转电机开关中关键部件的绝对拷贝数,获得比以前的相对估计大得多的数字。我们的结果表明了鞭毛开关适应性重塑的新机制,并为更新开关的构象传播模型提供了新的见解。
The cytoplasmic ring (C-ring) of the bacterial flagellar motor controls the motor rotation direction, thereby controlling bacterial run-and-tumble behavior. The C-ring has been shown to undergo adaptive remodeling in response to changes in motor directional bias. However, the stoichiometry and arrangement of the C-ring is still unclear due to contradiction between the results from fluorescence studies and cryo-electron microscopy (cryo-EM) structural analysis. Here, by using the copy number of FliG molecules (34) in the C-ring as a reference, we precisely measured the copy numbers of FliM molecules in motors rotating exclusively counterclockwise (CCW) and clockwise (CW). We surprisingly found that there are on average 45 and 58 FliM molecules in CW and CCW rotating motors, respectively, which are much higher than previous estimates. Our results suggested a new mechanism of C-ring adaptation, that is, extra FliM molecules could be bound to the primary C-ring with probability depending on the motor rotational direction. We further confirmed that all of the FliM molecules in the C-ring function in chemotaxis signaling transduction because all of them could be bound by the chemotactic response regulator CheY-P. Our measurements provided new insights into the structure and arrangement of the flagellar switch. IMPORTANCE The bacterial flagellar switch can undergo adaptive remodeling in response to changes in motor rotation direction, thereby shifting its operating point to match the output of the chemotaxis signaling pathway. However, it remains unclear how the flagellar switch accomplishes this adaptive remodeling. Here, via precise fluorescence studies, we measured the absolute copy numbers of the critical component in the switch for motors rotating counterclockwise and clockwise, obtaining much larger numbers than previous relative estimates. Our results suggested a new mechanism of adaptive remodeling of the flagellar switch and provided new insights for updating the conformation spread model of the switch.