Elastic coupling power stroke mechanism of the F1-ATPase molecular motor

Journal article

The angular velocity profile of the 120° F1-ATPase power stroke was resolved as a function of temperature from 16.3 to 44.6 °C using a ΔμATP = −31.25 kBT at a time resolution of 10 μs. Angular velocities during the first 60° of the power stroke (phase 1) varied inversely with temperature, resulting in negative activation energies with a parabolic dependence. This is direct evidence that phase 1 rotation derives from elastic energy (spring constant, κ = 50 kBT·rad−2). Phase 2 of the power stroke had an enthalpic component indicating that additional energy input occurred to enable the γ-subunit to overcome energy stored by the spring after rotating beyond its 34° equilibrium position. The correlation between the probability distribution of ATP binding to the empty catalytic site and the negative Ea values of the power stroke during phase 1 suggests that this additional energy is derived from the binding of ATP to the empty catalytic site. A second torsion spring (κ = 150 kBT·rad−2; equilibrium position, 90°) was also evident that mitigated the enthalpic cost of phase 2 rotation. The maximum ΔGǂ was 22.6 kBT, and maximum efficiency was 72%. An elastic coupling mechanism is proposed that uses the coiled-coil domain of the γ-subunit rotor as a torsion spring during phase 1, and then as a crankshaft driven by ATP-binding–dependent conformational changes during phase 2 to drive the power stroke.

Authors: Martin, JL; Ishmukhametov, R; Spetzler, D; Hornung, T; Frasch, WD

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: National Academy of Sciences
• Journal: Proceedings of the National Academy of Sciences
• Volume: 115
• Issue: 22
• Pages: 5750-5755
• Place of publication: United States
• Publication date: 2018-05-14
• Acceptance date: 2018-04-16
• DOI: 10.1073/pnas.1803147115
• EISSN: 1091-6490
• ISSN: 0027-8424
• Pmid: 29760063
• Language: English
• Keywords: power stroke mechanism; F1-ATPase; FOF1 ATP synthase; single molecule; FFR; F-type ATP synthase