[EWS1-2] Structural differences of the flagellar rotor in the counterclockwise and clockwise rotation states
Bacteria flagellar motor can rotate in counterclockwise (CCW) or clockwise (CW) direction. The motor is composed of the rotor and stator, and the rotor-stator interaction is essential for motor torque. The C-ring, one of the rotor components, is composed of three proteins, FliG FliM and FliN, and is involved in switching rotational directions by receiving the chemotactic signal. The C-terminal domain of FliG (FliGc) interacts with the stator and its conformational changes alter the interaction surface between the FliG and stator and induce the rotational switching. CheY phosphate (CheY-P), one of the chemotaxis (Che) proteins, binds to FliM and induces the conformational change of FliGc, resulting that the motor rotation changes from CCW to CW. When CheY dissociates from FliM due to dephosphorization, the motor rotates CCW direction. However, the conformational change of the C-ring caused by the CheY association and dissociation is not understood well. To investigate this conformational change, we performed cryo-electron tomography and subtomogram averaging for the CCW-biased (FliG-G214S) and CW-locked (FliG-G215A) motors. Compared with both motors, we found that the diameter at the top of the C-ring in the CW motor was larger than that in the CCW. Furthermore, the extra density at the outside of FliM was found in the G215A mutant, and we speculated that this density is CheY-P.