Stability of the Escherichia coli ATP synthase F₀F₁ complex is dependent on interactions between γGln-269 and the β subunit loop βAsp- 301-βAsp-305

The role of the conserved sequence motif ³⁰¹DDL-TDP³⁰⁶ in the F₀F₁ ATP synthase β subunit was assessed by mutagenic analysis in the Escherichia coli enzyme. Mutations gave variable effects on F₁ sector activity, stability, and membrane binding to the F₀ sector. Upon solubilization, F₁ sectors of the βD302E and βD305E mutants (βAsp-302 and βAsp-305 replaced by glutamate) dissociated into subunits, while mutants with other β305 substitutions failed to assemble. Membrane ATPase activities of β301 and 302 mutants were 20-70% of wild type. Replacements of the γ subunit Gln-269 had similar effects. The membrane ATPase activities of the γQ269E or γQ269D mutants were significantly lower and their F₁ sectors dissociated into subunits upon solubilization. These results suggest that the β301-305 loop and the γ subunit region around Gln-269 form a key region for the assembly of α₃β₃γ complex. These results are consistent with the X- ray crystallographic structure of bovine F₁ (J.P. Abrahams, A. G. W. Leslie, R. Lutter, and J. E. Walker (1994) Nature 370, 621-628) where the β³⁰¹DDLTD³⁰⁵ loop directly interacts with γGln-269.