title: Mechanochemical Energy Transduction during the Main Rotary Step in the Synthesis Cycle of F1-ATPase.
abstract: F1-ATPase is a highly efficient molecular motor that can synthesize ATP driven by a mechanical torque. Its ability to function reversibly in either direction requires tight mechanochemical coupling between the catalytic domain and the rotating central shaft, as well as temporal control of substrate binding and product release. Despite great efforts and significant progress, the molecular details of this synchronized and fine-tuned energy conversion mechanism are not fully understood. Here, we use extensive molecular dynamics simulations to reconcile recent single-molecule experiments with structural data and provide a consistent thermodynamic, kinetic and mechanistic description of the main rotary substep in the synthetic cycle of mammalian ATP synthase. The calculated free energy profiles capture a discrete pattern in the rotation of the central γ-shaft, with a metastable intermediate located-consistently with recent experimental findings-at 70° relative to the X-ray position. We identify this rotary step as the ATP-dependent substep, and find that the associated free energy input supports the mechanism involving concurrent nucleotide binding and release. During the main substep, our simulations show no significant opening of the ATP-bound β subunit; instead, we observe that mechanical energy is transmitted to its nucleotide binding site, thus lowering the affinity for ATP. Simultaneously, the empty subunit assumes a conformation that enables the enzyme to harness the free energy of ADP binding to drive ATP release. Finally, we show that ligand exchange is regulated by a checkpoint mechanism, an apparent prerequisite for high efficiency in protein nanomotors.
authors.affiliation: Department of Physical Chemistry, Gdansk University of Technology , ul. Narutowicza 11/12, 80-233 Gdańsk, Poland.
authors.forename: Jacek
authors.initials: J
authors.lastname: Czub
authors.affiliation: Department of Physical Chemistry, Gdansk University of Technology , ul. Narutowicza 11/12, 80-233 Gdańsk, Poland.
authors.forename: Miłosz
authors.identifier: 0000-0003-4990-8629
authors.initials: M
authors.lastname: Wieczór
authors.affiliation: Department of Physical Chemistry, Gdansk University of Technology , ul. Narutowicza 11/12, 80-233 Gdańsk, Poland.
authors.forename: Bartosz
authors.initials: B
authors.lastname: Prokopowicz
authors.affiliation: Department of Theoretical and Computational Biophysics, Max Planck Institute for Biophysical Chemistry , Am Fassberg 11, 37077 Göttingen, Germany.
authors.forename: Helmut
authors.initials: H
authors.lastname: Grubmüller
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D056004:Molecular Dynamics Simulation; D006180:Proton-Translocating ATPases / Q000737:chemistry / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D000255:Adenosine Triphosphate; D006180:Proton-Translocating ATPases