Clarification of the energy and signal transduction of bacterial flagellar motor using hybrid motor

细菌鞭毛马达是一种旋转分子机器，它旋转螺旋丝，推动许多种类的游动细菌。转子是细胞质膜上的一组直径达45nm的环；定子包含约 10 个扭矩产生单元，固定在转子周边的细胞壁上 4、5。电机的自由能源是穿过细胞质膜的离子向内的电化学梯度，分别是 H1 驱动电机和 Na1 驱动电机的质子动力或钠动力。在这里，我们展示了大肠杆菌6中Na1驱动的嵌合鞭毛马达在低钠动力和少量扭矩产生单元的受控表达下的步进运动。我们观察到每转 26 步，这与 FliG 蛋白环的周期性一致，FliG 蛋白环是转子上扭矩产生的位点 7, 8。尽管不存在鞭毛开关蛋白 CheY，但向后的步骤表明每步自由能的微小变化，类似于单个离子传输。

The bacterial flagellar motor is a rotary molecular machine that rotates the helical filaments that propel many species of swimming bacteria. The rotor is a set of rings up to 45nm in diameter in the cytoplasmic membrane3 ; the stator contains about ten torque generating units anchored to the cell wall at the perimeter of the rotor4, 5. The free-energy source for the motor is an inward directed electrochemical gradient of ions across the cytoplasmic membrane, the protonmotive force or sodium-motive force for H1-driven and Na1-driven motors, respectively. Here we demonstrate a stepping motion of a Na1-driven chimaeric flagellar motor in Escherichia coli6 at low sodium-motive force and with controlled expression of a small number of torque-generating units. We observe 26 steps per revolution, which is consistent with the periodicity of the ring of FliG protein, the proposed site of torque generation on the rotor7, 8. Backwards steps despite the absence of the flagellar switching protein CheY indicate a small change in free energy per step, similar to that of a single ion transit.