Assembly of the Escherichia coli F_oF₁ ATP synthase involves distinct subcomplex formation

The ATP synthase (F_oF₁) of Escherichia coli couples the translocation of protons across the cytoplasmic membrane by F_o to ATP synthesis or hydrolysis in F₁. Whereas good knowledge of the nanostructure and the rotary mechanism of the ATP synthase is at hand, the assembly pathway of the 22 polypeptide chains present in a stoichiometry of ab₂c₁₀α₃β₃γδϵ has so far not received sufficient attention. In our studies, mutants that synthesize different sets of F_oF₁ subunits allowed the characterization of individually formed stable subcomplexes. Furthermore, the development of a time-delayed in vivo assembly system enabled the subsequent synthesis of particular missing subunits to allow the formation of functional ATP synthase complexes. These observations form the basis for a model that describes the assembly pathway of the E. coli ATP synthase from pre-formed subcomplexes, thereby avoiding membrane proton permeability by a concomitant assembly of the open H⁺-translocating unit within a coupled F_oF₁ complex.