In Escherichia coli, the chemotaxis response regulator CheY-P binds to FliM, a component of the switch complex at the base of the bacterial flagellar motor, to modulate the direction of motor rotation. The bacterial flagellar motor is ultrasensitive to the concentration of unbound CheY-P in the cytoplasm. CheY-P binds to FliM molecules both in the cytoplasm and on the motor. As the concentration of FliM unavoidably varies from cell to cell, leading to a variation of unbound CheY-P concentration in the cytoplasm, this raises the question whether the flagellar motor is robust against this variation, that is, whether the rotational bias of the motor is more or less constant as the concentration of FliM varies. Here, we showed that the motor is robust against variations of the concentration of FliM. We identified adaptive remodeling of the motor as the mechanism for this robustness. As the level of FliM molecules changes, resulting in different amounts of the unbound CheY-P molecules, the motor adaptively changes the composition of its switch complex to compensate for this effect.IMPORTANCE The bacterial flagellar motor is an ultrasensitive motor. Its output, the probability of the motor turning clockwise, depends sensitively on the occupancy of the protein FliM (a component on the switch complex of the motor) by the input CheY-P molecules. With a limited cellular pool of CheY-P molecules, cell-to-cell variation of the FliM level would lead to large unwanted variation of the motor output if not compensated. Here, we showed that the motor output is robust against the variation of FliM level and identified the adaptive remodeling of the motor switch complex as the mechanism for this robustness.

中文翻译：

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超灵敏电机的坚固性。

在大肠杆菌中，趋化性反应调节剂CheY-P与FliM结合，FliM是细菌鞭毛马达底部的开关复合体的一个成分，可调节马达旋转的方向。细菌鞭毛运动对细胞质中未结合的CheY-P的浓度非常敏感。CheY-P在细胞质和运动中均与FliM分子结合。由于FliM的浓度不可避免地在每个细胞之间变化，从而导致细胞质中未结合的CheY-P浓度发生变化，这引起了一个问题，即鞭毛马达是否对这种变化具有鲁棒性，即马达的旋转偏置是否当FliM的浓度变化时，该常数大致恒定。在这里，我们证明了电动机对于FliM浓度变化具有鲁棒性。我们将电动机的自适应重塑确定为这种鲁棒性的机制。随着FliM分子水平的变化，导致未结合的CheY-P分子数量不同，该电动机可自适应地改变其开关复合物的成分以补偿这种效应。重要意义细菌鞭毛电动机是一种超灵敏电动机。它的输出，即电动机顺时针旋转的概率，敏感地取决于输入的CheY-P分子对蛋白质FliM（电动机的开关复合体上的一个成分）的占有率。对于有限的CheY-P分子细胞池，如果不进行补偿，FliM水平的细胞间变化将导致电机输出产生较大的不希望有的变化。这里，