Interacting cytoplasmic loops of subunits a and c of Escherichia coli F1F0 ATP synthase gate H+ transport to the cytoplasm.

H(+)-transporting F1F0 ATP synthase catalyzes the synthesis of ATP via coupled rotary motors within F0 and F1. H(+) transport at the subunit a-c interface in transmembranous F0 drives rotation of a cylindrical c10 oligomer within the membrane, which is coupled to rotation of subunit γ within the α3β3 sector of F1 to mechanically drive ATP synthesis. F1F0 functions in a reversible manner, with ATP hydrolysis driving H(+) transport.

Half channels mediating H(+) transport and the mechanism of gating in the Fo sector of Escherichia coli F1Fo ATP synthase.

H(+)-transporting F1Fo ATP synthase catalyzes the synthesis of ATP via coupled rotary motors within Fo and F1. H(+) transport at the subunit a-c interface in trans-membranous Fo drives rotation of the c-ring within the membrane, with subunit c being bound in a complex with the γ and ε subunits extending from the membrane. Finally, the rotation of subunit γ within the α3β3 sector of F1 mechanically drives ATP synthesis within the catalytic sites.

Residues in the polar loop of subunit c in Escherichia coli ATP synthase function in gating proton transport to the cytoplasm.

Rotary catalysis in F1F0 ATP synthase is powered by proton translocation through the membrane-embedded F0 sector. Proton binding and release occur in the middle of the membrane at Asp-61 on the second transmembrane helix (TMH) of subunit c, which folds in a hairpin-like structure with two TMHs. Previously, the aqueous accessibility of Cys substitutions in the transmembrane regions of subunit c was probed by testing the inhibitory effects of Ag(+) or Cd(2+) on function, which revealed extensive aqueous access in the region around Asp-61 and on the half of TMH2 extending to the cytoplasm.

Obstruction of transmembrane helical movements in subunit a blocks proton pumping by F1Fo ATP synthase.

Subunit a plays a key role in promoting H(+) transport-coupled rotary motion of the subunit c ring in F1Fo ATP synthase. H(+) binding and release occur at Asp-61 in the middle of the second transmembrane helix (TMH) of Fo subunit c. H(+) are thought to reach cAsp61 via aqueous half-channels formed by TMHs 2-5 of subunit a.

Interactions between subunits a and b in the rotary ATP synthase as determined by cross-linking.

The interaction of the membrane traversing stator subunits a and b of the rotary ATP synthase was probed by substitution of a single Cys into each subunit with subsequent Cu(2+) catalyzed cross-linking. Extensive interaction between the transmembrane (TM) region of one b subunit and TM2 of subunit a was indicated by cross-linking with 6 Cys pairs introduced into these regions. Additional disulfide cross-linking was observed between the N-terminus of subunit b and the periplasmic loop connecting TM4 and TM5 of subunit a.