Essential arginine residue of the F0-a subunit in F0F1-ATP synthase has a role to prevent the proton shortcut without c-ring rotation in the F0 proton channel

In F0F1 (F0F1-ATP synthase), proton translocation through F drives rotation of the oligomer ring of F-0-c subunits (c-ring) relative to F-0-a. Previous reports have indicated that a conserved arginine residue in F-0-a plays a critical role in the proton transfer at the F-0-a/c-ring interface. Indeed, we show in the present study that thermophilic F(0)F(1)s with substitution of this arginine (aR169) to other residues cannot catalyse protoncoupled reactions. However, mutants with substitution of this arginine residue by a small (glycine, alanine, valine) or acidic (glutamate) residue mediate the passive proton translocation. This translocation requires an essential carboxy group of F-0-c (cE56) since the second mutation (cE56Q) blocks the translocation. Rotation of the c-ring is not necessary because the same arginine mutants of the 'rotation-impossible' (c(10)-a)F0F1, in which the c-ring and F-0-a are fused to a single polypeptide, also exhibits the passive proton translocation. The mutant (aR169G/Q217R), in which the arginine residue is transferred to putatively the same topological position in the F-0-a structure, can block the passive proton translocation. Thus the conserved arginine residue in F-0-a ensures proton-coupled c-ring rotation by preventing a futile proton shortcut.