Chemomechanical Coupling in Single-Molecule F-Type ATP Synthase

An extremely small reaction chamber with a volume of a few femtoliters was developed for a highly sensitive detection of biological reaction. By encapsulating a single F1-ATPase (F1) molecule with ADP and an inorganic phosphate in the chamber, the chemomechanical coupling efficiency of ATP synthesis catalyzed by reversely rotated F1was successfully determined (Rondelez et al., 2005a, Nature, 444, 773–777). While the α < eqid1 > β < eqid2 > γ subcomplex of F1generated ATP with a low efficiency (∼10%), inclusion of the ε subunit into the subcomplex enhanced the efficiency up to 77%. This raises a new question about the mechanism of F0F1-ATP synthase (F0F1): How does the ε subunit support the highly coupled ATP synthesis of F1? To address this question, we measured the conformational dynamics of the ε subunit using fluorescence resonance energy transfer (FRET) at the single-molecule level. The experimental data revealed ε changes the conformation of its C-terminus helices in a nucleotide-dependent manner. It is plausible that the conformational change of ε switches the catalytic mode of F0F1for highly coupled ATP synthesis.