Figure 6.

Side view (top row) and view from the membrane side with the c-ring and subunit a omitted of the three cryo-EM structural states of EcF_OF₁ [12]. State 1 (PDB-id: 5T4O, left), state 2 (PDB-id: 5T4P, middle), and state 3 (PDB-id: 5T4Q, right) correspond to FRET levels M, L, and H, respectively (as in Figure 4). In each image, the FRET-donor position at ε56 is marked with a green sphere and the FRET-acceptor position at b64 is marked with a red sphere. The portions of subunit ε and γ that extends beyond the diameter of the c-ring must pass through the narrow gap created by the peripheral stalk during rotation from state 3 to state 1, and during rotation from state 1 to state 2, respectively. The subunit coloring is the same as in Figure 1.