Internal and external components of the bacterial flagellar motor rotate as a unit
Significance Intracellular components of the bacterial flagellar motor acted on by force generating elements of the stator to power rotation of the extracellular hook and filament have been visualized by EM. Their molecular composition is known, but their actual rotation has never been shown. Here, a method for bleaching and probing a fusion protein rigidly linked to one of the innermost components of the flagellar motor of Escherichia coli, FliN, was used to show that the components commonly thought to rotate as a unit actually do so. Most bacteria that swim, including Escherichia coli, are propelled by helical filaments, each driven at its base by a rotary motor powered by a proton or a sodium ion electrochemical gradient. Each motor contains a number of stator complexes, comprising 4MotA 2MotB or 4PomA 2PomB, proteins anchored to the rigid peptidoglycan layer of the cell wall. These proteins exert torque on a rotor that spans the inner membrane. A shaft connected to the rotor passes through the peptidoglycan and the outer membrane through bushings, the P and L rings, connecting to the filament by a flexible coupling known as the hook. Although the external components, the hook and the filament, are known to rotate, having been tethered to glass or marked by latex beads, the rotation of the internal components has remained only a reasonable assumption. Here, by using polarized light to bleach and probe an internal YFP FliN fusion, we show that the innermost components of the cytoplasmic ring rotate at a rate similar to that of the hook.
Proceedings of the National Academy of Sciences