2XQS: Microscopic Rotary Mechanism Of Ion Translocation In The Fo 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 A, 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.
PDB ID: 2XQSDownload
MMDB ID: 85718
PDB Deposition Date: 2010/9/7
Updated in MMDB: 2010/10
Experimental Method:
x-ray diffraction
Resolution: 3  Å
Source Organism:
Similar Structures:
Biological Unit for 2XQS: pentadecameric; determined by author and by software (PISA)
Molecular Components in 2XQS
Label Count Molecule
Proteins (15 molecules)
ATP Synthase C Chain
Molecule annotation
Chemicals (108 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB