Subunit rotation of ATP synthase embedded in membranes: a or β subunit rotation relative to the c subunit ring

ATP synthase F_oF₁ (α₃β₃γδɛab₂c_10-14) couples an electrochemical proton gradient and a chemical reaction through the rotation of its subunit assembly. In this study, we engineered F_oF₁ to examine the rotation of the catalytic F₁ β or membrane sector F_o a subunit when the F_o c subunit ring was immobilized; a biotin-tag was introduced onto the β or a subunit, and a His-tag onto the c subunit ring. Membrane fragments were obtained from Escherichia coli cells carrying the recombinant plasmid for the engineered F_oF₁ and were immobilized on a glass surface. An actin filament connected to the β or a subunit rotated counterclockwise on the addition of ATP, and generated essentially the same torque as one connected to the c ring of F_oF₁ immobilized through a His-tag linked to the α or β subunit. These results established that the γɛc_10-14 and α₃β₃δab₂ complexes are mechanical units of the membrane-embedded enzyme involved in rotational catalysis.