Chemomechanical coupling of human mitochondrial F1-ATPase motor

A single-molecule study of the dwell times and other features along the full rotation for the human mitochondrial F 1 -ATPase positions the catalytic events (ATP binding, P i release and ATP hydrolysis) and reveals differences from the bacterial system. The rotary motor enzyme F 1 -ATPase (F 1 ) is a catalytic subcomplex of F o F 1 -ATP synthase that produces most of the ATP in respiring cells. Chemomechanical coupling has been studied extensively for bacterial F 1 but very little for mitochondrial F 1 . Here we report ATP-driven rotation of human mitochondrial F 1 . A rotor-shaft γ-subunit in the stator α 3 β 3 ring rotates 120° per ATP with three catalytic steps: ATP binding to one β-subunit at 0°, inorganic phosphate (P i ) release from another β-subunit at 65° and ATP hydrolysis on the third β-subunit at 90°. Rotation is often interrupted at 90° by persistent ADP binding and is stalled at 65° by a specific inhibitor azide. A mitochondrial endogenous inhibitor for F o F 1 -ATP synthase, IF1, blocks rotation at 90°. These features differ from those of bacterial F 1 , in which both ATP hydrolysis and P i release occur at around 80°, demonstrating that chemomechanical coupling angles of the γ-subunit are tuned during evolution.