Cavendish Laboratory, University of Cambridge, Cambridge, CB3 0HE, UK.
Sci Rep. 2020 Apr 28;10(1):7127. doi: 10.1038/s41598-020-63330-y.
The role of rotational molecular motors of the ATP synthase class is integral to the metabolism of cells. Yet the function of FliI-FliJ complex, a homolog of the F ATPase motor, within the flagellar export apparatus remains unclear. We use a simple two-state model adapted from studies of linear molecular motors to identify key features of this motor. The two states are the 'locked' ground state where the FliJ coiled coil filament experiences angular fluctuations in an asymmetric torsional potential, and a 'free' excited state in which FliJ undergoes rotational diffusion. Michaelis-Menten kinetics was used to treat transitions between these two states, and obtain the average angular velocity of the unloaded FliJ filament within the FliI stator: ω ≈ 9.0 rps. The motor was then studied under external counter torque conditions in order to ascertain its maximal power output: P ≈ 42 kT/s (or 102 kW/mol), and the stall torque: G ≈ 3 kT/rad (or 0.01 nN·nm/rad). Two modes of action within the flagellar export apparatus are proposed, in which the motor performs useful work either by continuously 'grinding' through the resistive environment of the export gate, or by exerting equal and opposite stall force on it. In both cases, the resistance is provided by flagellin subunits entering the flagellar export channel prior to their unfolding. We therefore propose that the function of the FliI-FliJ complex is to lower the energy barrier, and therefore assist in unfolding of the flagellar proteins before feeding them into the transport channel.
旋转分子马达在 ATP 合酶类中的作用对于细胞的新陈代谢至关重要。然而，鞭毛出口装置中 FliI-FliJ 复合物（F ATPase 马达的同源物）的功能仍不清楚。我们使用一种简单的二态模型，该模型改编自线性分子马达的研究，以确定该马达的关键特征。这两个状态是“锁定”的基态，其中 FliJ 卷曲螺旋丝在非对称扭转势中经历角度波动，以及“自由”的激发态，其中 FliJ 经历旋转扩散。米氏动力学用于处理这两种状态之间的转变，并获得 FliI 定子中未加载的 FliJ 细丝的平均角速度：ω≈9.0 rps。然后，在外部反向扭矩条件下研究了该马达，以确定其最大功率输出：P≈42 kT/s（或 102 kW/mol），以及失速扭矩：G≈3 kT/rad（或 0.01 nN·nm/rad）。提出了在鞭毛出口装置中两种作用模式，其中马达通过连续“研磨”出口门的阻力环境或对其施加相等且相反的失速力来执行有用的工作。在这两种情况下，阻力由在其展开之前进入鞭毛出口通道的鞭毛蛋白亚基提供。因此，我们提出 FliI-FliJ 复合物的功能是降低能量势垒，从而有助于在将鞭毛蛋白送入运输通道之前展开它们。
