Subunit Rotation of ATP Synthase Embedded in Membranes: a or β Subunit Rotation Relative to the c Subunit Ring

ATP synthase FoF 1(α3β3γδε ab2c 10-14) couples an electrochemical proton gradient and a chemical reaction through the rotation of its subunit assembly. In this study, we engineered FoF 1to examine the rotation of the catalytic F1β or membrane sector Foa subunit when the Foc 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 FoF 1and 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 FoF 1immobilized through a His-tag linked to the α or β subunit. These results established that the γε c10-14and α3β3δ ab2complexes are mechanical units of the membrane-embedded enzyme involved in rotational catalysis.