[EWS1-1] Mechanism of the stator-rotor interactions essential for bacterial flagellar rotation
The bacterial flagellum is a unique motility organelle that functions as an ion-driven rotary motor. The rotor and stator parts of the flagellar motor are located in the cytoplasmic membrane. The stator units conduct an ion-influx, and that ion-influx induces conformational change of the stator unit to generate rotor torque. Although electrostatic interactions between the stator A protein (PomA in Vibrio, MotA in E. coli) and the rotor protein FliG have been revealed by genetic analyses, it have not been demonstrated directly. Here, we show direct evidence for the interaction by using site-directed photo- and disulfide-crosslinking approaches. We introduced a UV-reactive amino acid, p-benzoyl-L-phenylalanine (pBPA), into PomA or FliG in cells. After UV irradiation, pBPA-incorporated PomA, especially K89pBPA, formed a crosslink with FliG, suggesting that it is in close to FliG. The cells stopped swimming by UV irradiation, and the isolated hook-basal body contained the crosslinked products, suggesting that the crosslink occurred, at least in part, in the motor. pBPA incorporated to FliG R281 or D288 formed crosslinks with MotA. PomA K89C formed a disulfide crosslink with FliG R281C or D288C. These results provide the first biochemical evidence of physical interaction between specific residues in FliG and PomA/MotA.