Figure 1.

Models of FRET-labeled F_oF₁-ATP synthase in the three rotary states of the γ- and ε-subunits with respect to the F₁ subunits α₃β₃δ (white and dark gray) and F_o subunits b₂ (light gray, peripheral stalk). (A–C) cryoEM structures in the presence of 10 mM ADP with subunits b₂ oriented to the right side [35]. (D–F) cryoEM structures in the presence of 10 mM ATP with subunits b₂ oriented to the back side [36]. Green spheres are positions of the S atom of cysteine εH56C on the ε-subunit (dark green) labeled with FRET donor Cy3B, red spheres are modeled positions of the S atom of cysteine a276C on the a-subunit (orange) labeled with FRET acceptor Alexa Fluor 647. The central rotary γ-subunit of the F₁ domain is shown in cyan, and c-subunits of the F_o domain in dark blue and in light blue, embedded in the membrane (indicated by the gray disc). During ATP hydrolysis, the rotary states move sequentially in the order …→state #1 (D)→state #2 (E)→state #3 (F)→… for the counter-clockwise rotation direction when viewed from the bottom.