报告人：Junhua Yuan，哈佛大学

报告时间：6月30日下午2:30

报告地点：理科楼三楼报告厅

报告题目：Dynamics of bacterial propulsion: Behavior of the flagellar rotary motor near zero load

报告摘要：Flagellated bacteria swim by rotating thin helical filaments, each driven at its base by a reversible rotary motor embedded in the cell wall and powered by an ion flux. The motor contains about 20 different kinds of proteins, comprising a rotor driven by torque-generating units, a drive shaft, a bushing, a universal joint (the hook), and a variable-pitch propeller (the flagellar filament). We developed a new technique that allows systematic study of the motor near zero load. Sixty-nanometer-diameter gold spheres were attached to motors lacking flagellar filaments, and a novel laser darkfield setup was used to monitor their rotation. Paralyzed motors without torque- generating units were resurrected by adding torque generating units to the motor one at a time. In contrast to the incremental increase in rotation rate observed at high load, the rotation rate jumped to the maximum value upon addition of the first torque-generating unit. Switching properties of the flagellar motor near zero load also were investigated, and the switching rates showed a linear dependence on motor torque. Rotation in either direction (clockwise: CW or counterclockwise: CCW) has been thought to be symmetric, exhibiting the same torques and speeds. We measured the torque-speed relationship across all load regimes for CW rotation, and found that the torque decreases linearly with speed, a result remarkably different from that for CCW rotation. This work provides further insights into the torque- generating and switching mechanisms, and places tighter constraints on possible motor models.