High-pressure Microscopy For Modulating The Torque Generation Of Bacterial Flagellar Motors

Abstract

The bacterial flagellar motor converts the specific ion flux across the cell membrane to the rotational motion. The torque generation is achieved by the intermolecular interaction between rotor and stator complexes. The motor can spin both directions; binding activated CheY molecules induces switching from counter-clockwise (CCW) to clockwise (CW). Here, we show a novel assay that changes the rotational speed and direction of the flagellar motor by specially designed high-pressure microscopy. E. coli cells lacking cheY that rotate exclusively in the CCW direction, were tethered by their flagellum to the observation window of high-pressure chamber. At less than 800 atm, all cells rotated in the CCW direction and their speeds were not affected seriously. At more than 1000 atm, some cells started to rotate in the CW direction, and the rotational speed in both directions decreased steeply with pressure. Application of pressure generally works to modify the intermolecular interaction between protein and water molecules, resulting in changing the structure and function of molecular machines. Thus, applied pressure seems to modify directly the intermolecular interaction between rotor and stator units. The pressure-induced effects could inhibit the torque generation of the flagellar motor, and change the rotational direction, as if the activated CheY molecules bind to the rotor.