Conformational changes in the Escherichia coli ATP synthase b-dimer upon binding to F₁-ATPase

Conformational changes within the subunit b-dimer of the E. coli ATP synthase occur upon binding to the F₁ sector. ESR spectra of spin-labeled b at room temperature indicated a pivotal point in the b-structure at residue 62. Spectra of frozen b ± F₁ and calculated interspin distances suggested that where contact between b ₂ and F₁ occurs (above about residue 80), the structure of the dimer changes minimally. Between b-residues 33 and 64 inter-subunit distances in the F₁-bound b-dimer were found to be too large to accommodate tightly coiled coil packing and therefore suggest a dissociation and disengagement of the dimer upon F₁-binding. Mechanistic implications of this "bubble" formation in the tether domain of ATP synthase b ₂ are discussed.