The molecular structure of an axle-less F1-ATPase

F1Fo ATP synthase is a molecular rotary motor that can generate ATP using a transmembrane proton motive force. Isolated F1-ATPase catalytic cores can hydrolyse ATP, passing through a series of conformational states involving rotation of the central gamma rotor subunit and the opening and closing of the catalytic (3 subunits. Cooperativity in F1-ATPase has long thought to be conferred through the gamma subunit, with three key interaction sites between the gamma and (3 subunits being identified. Single molecule studies have demonstrated that the F1 complexes lacking the gamma axle still "rotate" and hydrolyse ATP, but with less efficiency. We solved the cryogenic electron microscopy structure of an axle-less Bacillus sp. PS3 F1-ATPase. The unexpected binding-dwell conformation of the structure in combination with the observed lack of interactions between the axle-less gamma and the open (3 subunit suggests that the complete gamma subunit is important for coordinating efficient ATP binding of F1-ATPase.