Fig. 4.

Model of the dimeric-mitochondrial ATP synthase: possible localization of the IF₁ protein and its movements to allow rotation of the central stalk during ATP synthesis. The model depicts the overall shape of the dimeric ATP synthase molecule that we observed for the bovine mitochondrial enzyme [54]. The dimeric interface involves F₀ subunits (e and g) and two protein bridges, one at the F₀–F₀ side of unknown composition (question mark) and another at the F₁–F₁ interface where the second stalks (not shown for clarity) and the IF₁ protein (red) are likely to be located. The C-terminal side of the IF₁ molecule is assumed to cross the dimer interface and to stabilize the dimer by interacting with subunits OSCP [65] and possibly subunits of the second stalk. The N-terminal inhibitory domain that in the absence of the proton gradient blocks rotation of the central stalk by entering at an α–β–γ interface (Fig. 2) is removed from this position and exposed into the media after establishment of a transmembrane proton gradient, thus allowing rotation of the central stalk during ATP synthesis. The F₁ structures were constructed from the bovine F₁-DCCD coordinates available (PDF code 1E79)