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 F-1-ATPase (F-1) molecule with ADP and all inorganic phosphate in the chamber, the chemomechanical coupling efficiency of ATP synthesis catalyzed by reversely rotated F-1 was successfully determined (Rondelez et al., 2005a, Nature, 444, 773-777). While the alpha(3)beta(3)gamma subcomplex of F-1 generated ATP with a low efficiency (similar to 10%), inclusion of the epsilon 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 e subunit support the highly coupled ATP synthesis of F-1? To address this question, we measured the conformational dynamics of the epsilon subunit using fluorescence resonance energy transfer (FRET) at the single-molecule level. The experimental data revealed epsilon changes the conformation of its C-terminus helices in a nucleotide-dependent manner. It is plausible that the conformational change of epsilon switches the catalytic mode of F0F1 for highly coupled ATP synthesis.