Abstract
The rotation of F(1)F(o)-ATP synthase is powered by the proton motive force across the energy-transducing membrane. The protein complex functions like a turbine; the proton flow drives the rotation of the c-ring of the transmembrane F(o) domain, which is coupled to the ATP-producing F(1) domain. The hairpin-structured c-protomers transport the protons by reversible protonation/deprotonation of a conserved Asp/Glu at the outer transmembrane helix (TMH). An open question is the proton transfer pathway through the membrane at atomic resolution. The protons are thought to be transferred via two half-channels to and from the conserved cAsp/Glu in the middle of the membrane. By molecular dynamics simulations of c-ring structures in a lipid bilayer, we mapped a water channel as one of the half-channels. We also analyzed the suppressor mutant cP24D/E61G in which the functional carboxylate is shifted to the inner TMH of the c-protomers. Current models concentrating on the "locked" and "open" conformations of the conserved carboxylate side chain are unable to explain the molecular function of this mutant. Our molecular dynamics simulations revealed an extended water channel with additional water molecules bridging the distance of the outer to the inner TMH. We suggest that the geometry of the water channel is an important feature for the molecular function of the membrane part of F(1)F(o)-ATP synthase. The inclination of the proton pathway isolates the two half-channels and may contribute to a favorable clockwise rotation in ATP synthesis mode.
Highlights
ATP synthase converts a transmembrane gradient of protons or Naϩ into chemical energy
Our molecular dynamics simulations revealed an extended water channel with additional water molecules bridging the distance of the outer to the inner transmembrane helix (TMH)
We suggest that the geometry of the water channel is an important feature for the molecular function of the membrane part of F1FoATP synthase
Summary
ATP synthase converts a transmembrane gradient of protons or Naϩ into chemical energy. Results: Molecular dynamics simulations mapped a water half-channel as part of the proton path. Significance: The geometry of the proton path is crucial in understanding the energy coupling of ATP synthase. The rotation of F1Fo-ATP synthase is powered by the proton motive force across the energy-transducing membrane. The protein complex functions like a turbine; the proton flow drives the rotation of the c-ring of the transmembrane Fo domain, which is coupled to the ATP-producing F1 domain. The protons are thought to be transferred via two half-channels to and from the conserved cAsp/Glu in the middle of the membrane. By molecular dynamics simulations of c-ring structures in a lipid bilayer, we mapped a water channel as one of the half-channels. We suggest that the geometry of the water channel is an important feature for the molecular function of the membrane part of F1FoATP synthase. The inclination of the proton pathway isolates the two half-channels and may contribute to a favorable clockwise rotation in ATP synthesis mode
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