Torque Generation and Utilization in Motor Enzyme F0F1-ATP Synthase: HALF-TORQUE F

Background: ATP synthase (F 0 F 1 ) is a rotary motor enzyme. Results: F 1 with a short-sized helix-1 in β subunit rotates with half of the normal torque and supports reduced ATP synthesis activity. Conclusion: Helix-1 acts as a “pushrod” to generate torque, and torque-reduced F 0 F 1 retains the catalytic ability of ATP synthesis. Significance: Generation and utilization of the torque are crucial for motor enzymes. ATP synthase (F 0 F 1 ) is made of two motors, a proton-driven motor (F 0 ) and an ATP-driven motor (F 1 ), connected by a common rotary shaft, and catalyzes proton flow-driven ATP synthesis and ATP-driven proton pumping. In F 1 , the central γ subunit rotates inside the α 3 β 3 ring. Here we report structural features of F 1 responsible for torque generation and the catalytic ability of the low-torque F 0 F 1 . (i) Deletion of one or two turns in the α-helix in the C-terminal domain of catalytic β subunit at the rotor/stator contact region generates mutant F 1 s, termed F 1 (1/2)s, that rotate with about half of the normal torque. This helix would support the helix-loop-helix structure acting as a solid “pushrod” to push the rotor γ subunit, but the short helix in F 1 (1/2)s would fail to accomplish this task. (ii) Three different half-torque F 0 F 1 (1/2)s were purified and reconstituted into proteoliposomes. They carry out ATP-driven proton pumping and build up the same small transmembrane ΔpH, indicating that the final ΔpH is directly related to the amount of torque. (iii) The half-torque F 0 F 1 (1/2)s can catalyze ATP synthesis, although slowly. The rate of synthesis varies widely among the three F 0 F 1 (1/2)s, which suggests that the rate reflects subtle conformational variations of individual mutants.