Eiichiro Saita

Chemomechanical coupling of human mitochondrial F1-ATPase motor

The rotary motor enzyme F1-ATPase (F1) is a catalytic subcomplex of FoF1-ATP synthase that produces most of the ATP in respiring cells. Chemomechanical coupling has been studied extensively for bacterial F1 but very little for mitochondrial F1. Here we report ATP-driven rotation of human mitochondrial F1. A rotor-shaft γ-subunit in the stator α3β3 ring rotates 120° per ATP with three catalytic steps: ATP binding to one β-subunit at 0°, inorganic phosphate (Pi) 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 FoF1-ATP synthase, IF1, blocks rotation at 90°. These features differ from those of bacterial F1, in which both ATP hydrolysis and Pi release occur at around 80°, demonstrating that chemomechanical coupling angles of the γ-subunit are tuned during evolution.