Asymmetry in the F1-ATPase and its implications for the rotational cycle.
ATP synthase uses a rotary mechanism to carry out its cellular function of manufacturing ATP. The central gamma-shaft rotates inside a hexameric cylinder composed of alternating alpha- and beta-subunits. When operating in the hydrolysis direction under high frictional loads and low ATP concentrations, a coordinated mechanochemical cycle in the three catalytic sites of the beta-subunits rotates the gamma-shaft in three 120 degrees steps. At low frictional loads, the 120 degrees steps alternate with three ATP-independent substeps separated by approximately 30 degrees. We present a quantitative model that accounts for these substeps and show that the observed pauses are due to 1), the asymmetry of the F(1) hexamer that produces a propeller-like motion of the power-stroke and 2), the relatively tight binding of ADP to the catalytic sites.
Sun
Sean X
SX
Department of Mechanical Engineering and Whitaker Institute of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland, USA.
Wang
Hongyun
H
Oster
George
G
D000255:Adenosine Triphosphate / Q000737:chemistry*; D016880:Anisotropy; D001665:Binding Sites; D002462:Cell Membrane / Q000737:chemistry*; D003198:Computer Simulation; D019281:Dimerization; D004735:Energy Transfer; D017276:Friction; D008956:Models, Chemical; D008958:Models, Molecular; D015233:Models, Statistical; D020409:Molecular Motor Proteins / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D021122:Protein Subunits; D006180:Proton-Translocating ATPases / Q000737:chemistry*; D012399:Rotation; D013269:Stochastic Processes; D014783:Viscosity
D020409:Molecular Motor Proteins; D021122:Protein Subunits; D000255:Adenosine Triphosphate; D006180:Proton-Translocating ATPases