Microscopic rotary mechanism of ion translocation in the F(o) complex of ATP synthases.
The microscopic mechanism of coupled c-ring rotation and ion translocation in F(1)F(o)-ATP synthases is unknown. Here we present conclusive evidence supporting the notion that the ability of c-rings to rotate within the F(o) complex derives from the interplay between the ion-binding sites and their nonhomogenous microenvironment. This evidence rests on three atomic structures of the c(15) rotor from crystals grown at low pH, soaked at high pH and, after N,N'-dicyclohexylcarbodiimide (DCCD) modification, resolved at 1.8, 3.0 and 2.2 Å, respectively. Alongside a quantitative DCCD-labeling assay and free-energy molecular dynamics calculations, these data demonstrate how the thermodynamic stability of the so-called proton-locked state is maximized by the lipid membrane. By contrast, a hydrophilic environment at the a-subunit-c-ring interface appears to unlock the binding-site conformation and promotes proton exchange with the surrounding solution. Rotation thus occurs as c-subunits stochastically alternate between these environments, directionally biased by the electrochemical transmembrane gradient.
Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.
Denys
D
Pogoryelov
Alexander
A
Krah
Julian D
JD
Langer
Özkan
Ö
Yildiz
José D
JD
Faraldo-Gómez
Thomas
T
Meier
D001665:Binding Sites; D003460:Crystallization; D004024:Dicyclohexylcarbodiimide / Q000737:chemistry; D004734:Energy Metabolism / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000378:metabolism; D008563:Membrane Lipids / Q000737:chemistry; D008958:Models, Molecular; D020409:Molecular Motor Proteins / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D006180:Proton-Translocating ATPases / Q000378:metabolism*; D011522:Protons; D021241:Spectrometry, Mass, Electrospray Ionization; D053545:Spirulina / Q000737:chemistry; D013816:Thermodynamics; D014961:X-Ray Diffraction
D007477:Ions; D008563:Membrane Lipids; D020409:Molecular Motor Proteins; D011522:Protons; D004024:Dicyclohexylcarbodiimide; D006180:Proton-Translocating ATPases