Fig. 1. Structures and rotation mechanism of F_oF₁.

a Cryo-EM structure of F_oF₁ ATP synthase in the step-waiting conformation. Each subunit is colored differently. The F₁ domain contains three catalytic αβ dimers which surround the γ subunit. b, c Side views (upper) and bottom section views (lower) of the F₁ domain in the step-waiting (0°) and 81° structure, respectively. The three catalytic dimers are represented different colors: α_E (marine blue) and β_E (light blue), α_T (moss green) and β_T (light green), and α_D (purple) and β_D (light purple). The β_D subunit in step-waiting adopts a more open structure, termed as DHO. The γ subunits are represented as a gray tube in the center of both α₃β₃ sub-complexes. d A proposed scheme for chemo-mechanical coupling during a 120° rotation step of the F₁ domain driven by ATP. In this model, ATP binding to the F₁ domain immediately initiates the 80° rotation with an associated release of ADP. ATP is hydrolyzed at the 80° dwell position with no associated rotation of γ. It is the release of Pi from the enzyme which is suggested to drive the final 40° rotation.