Journal
NATURE CHEMICAL BIOLOGY
Volume 6, Issue 12, Pages 891-899Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/NCHEMBIO.457
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Funding
- DFG [EXC 115]
- DFG Collaborative Research Center [(S.F.B.) 807]
- European Science Foundation
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The microscopic mechanism of coupled c-ring rotation and ion translocation in F1F0-ATP synthases is unknown. Here we present conclusive evidence supporting the notion that the ability of c-rings to rotate within the F-0 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 angstrom, 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.
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