Stability of theEscherichia coliATP Synthase F0F1Complex Is Dependent on Interactions between γGln-269 and the β Subunit Loop βAsp-301–βAsp-305

The role of the conserved sequence motif301DDLTDP306in the F0F1ATP synthase β subunit was assessed by mutagenic analysis in theEscherichia colienzyme. Mutations gave variable effects on F1sector activity, stability, and membrane binding to the F0sector. Upon solubilization, F1sectors 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 F1sectors 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)Nature370, 621–628) where the β301DDLTD305loop directly interacts with γGln-269.