Dodecamer rotor ring defines H ⁺ /ATP ratio for ATP synthesis of prokaryotic V-ATPase from <i>Thermus thermophilus</i>

Abstract

ATP synthesis by V-ATPase from the thermophilic bacterium Thermus thermophilus driven by the acid-base transition was investigated. The rate of ATP synthesis increased in parallel with the increase in proton motive force (PMF) &gt;110 mV, which is composed of a difference in proton concentration (ΔpH) and the electrical potential differences (ΔΨ) across membranes. The optimum rate of synthesis reached 85 s −1 , and the H + /ATP ratio of 4.0 ± 0.1 was obtained. ATP was synthesized at a considerable rate solely by ΔpH, indicating ΔΨ was not absolutely required for synthesis. Consistent with the H + /ATP ratio, cryoelectron micrograph images of 2D crystals of the membrane-bound rotor ring of the V-ATPase at 7.0-Å resolution showed the presence of 12 V o -c subunits, each composed of two transmembrane helices. These results indicate that symmetry mismatch between the rotor and catalytic domains is not obligatory for rotary ATPases/synthases.