Fig. 6. Chemo-Mechanical cycle of V/A-ATPase driven by ATP hydrolysis.
The structures of V/A-ATPase viewed from the cytosolic side are shown as ribbon models. The coiled-coil of the DF subunits is shown in gray. The bound ATP molecules are highlighted in sphere representations. State1–1 and 1–2 of V2nuc are in equilibrium and are fluctuating. These structures transit to state1–1 and 1–2 of V3nuc by ATP binding to ABopen, without a 120° rotation step of the DF rotor. V3nuc in state1–1 and state1–2 are also in equilibrium. ATP hydrolysis at ABsemi and zipper motion at ABopen occur simultaneously. This triggers the transition of V3nuc in state1–2 to V2nuc state2–2 together with the 120° rotation step and simultaneous release of ADP and Pi. State2 of V2nuc returns to state1 via state3 of V2nuc by the same process. Asterisks indicate the structures which were not identified in this study.