Rotary substates of mitochondrial ATP synthase reveal the basis of flexible F 1 -F o coupling

Flexible domains in a well-oiled machine Motors convert one form of energy into another. For biological motors, adenosine triphosphate (ATP) serves as chemical energy and its hydrolysis is coupled to conformational changes that exert mechanical force. ATP synthases reverse this process in a multistep process: first converting an electrochemical gradient to rotational kinetic energy, and then coupling rotation to formation of high-energy phosphodiester bonds. Murphy et al. investigated these energy changes in the dimeric mitochondrial F 1 -F o ATP synthase from Polytomella sp., a unicellular alga. They solved high-resolution cryo–electron microscopy structures of the ATP synthase complex, extracting 13 rotational substates. This collection of structures revealed that the rotation of the F o ring and central stalk is coupled with partial rotations of the F 1 head. This flexibility may enable the head to better couple continuous rotation with discrete ATP synthesis events. Science , this issue p. eaaw9128