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Keywords:

  • Elastic-contractile model proteins;
  • Hydrophobic hydration;
  • Charge hydration;
  • apolar—polar repulsion;
  • Repulsive force;
  • Water-filled cleft;
  • Aqueous chamber;
  • Hydrophobic face of γ-rotor

Abstract

Thesis: Within the structurally-confined internal aqueous cavity of the F1-motor of ATP synthase, function results from free energy changes that shift the balance between interfacial charge hydration and interfacial hydrophobic hydration.

Transition state description: At the β-P end of ADP · Mg occurs an inorganic phosphate, Pi. This Pi resides at the base of a water-filled cleft that functions like an aperture to focus, into an aqueous chamber, a competition for hydration (an apolar—polar repulsion) between charged phosphate and hydrophobic surface of the γ-rotor. Two means available for the phosphate and the hydrophobic surface to improve their hydration free energies are physically to separate by rotation of the γ-rotor or chemically to combine Pi with ADP to form less charged ATP. This proposal derives from calculated changes in Gibbs free energy for hydrophobic association of amino acid side chains and chemical modifications thereof and from experimentally demonstrated water-mediated repulsion between hydrophobic and charged sites that resulted from extensive studies on designed elastic-contractile model proteins.