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Nat Chem Biol. 2010 Dec;6(12):891-9. doi: 10.1038/nchembio.457. Epub 2010 Oct 24.

Microscopic rotary mechanism of ion translocation in the F(o) complex of ATP synthases.

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1
Department of Structural Biology, Max Planck Institute of Biophysics, Frankfurt am Main, Germany.

Abstract

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.

PMID:
20972431
DOI:
10.1038/nchembio.457
[Indexed for MEDLINE]
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