Figure 4. Molecular basis of rotational switching.

a–c, An expanded view of the encircled region in Fig. 3e is shown with one coloured FliG polypeptide chain. E192 and A193 are shown as yellow and red spheres respectively. a, b, Transition from the closed to the open conformation of helix_MC. b, c, An alternative conformational change when helix_MC remains in the closed conformation. d, e, The FliG ring with the monomers in the FliG_MC and the FliG_FL crystal structures, respectively. Charged residues on torque helix_C5 are shown in blue (positive) and red (negative).