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

ATP synthase F(o)F(1) (α(3)β(3)γδɛab(2)c(10–14)) couples an electrochemical proton gradient and a chemical reaction through the rotation of its subunit assembly. In this study, we engineered F(o)F(1) to examine the rotation of the catalytic F(1) 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(o)F(1) 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(o)F(1) immobilized through a His-tag linked to the α or β subunit. These results established that the γɛc(10–14) and α(3)β(3)δab(2) complexes are mechanical units of the membrane-embedded enzyme involved in rotational catalysis.