Intergenic suppression of the γM23K uncoupling mutation in F0F1 ATP synthase by βGlu-381 substitutions: The role of the β380DELSEED386 segment in energy coupling

We previously demonstrated that the Escherichia coli F₀F₁-ATP synthase mutation, γM23K, caused increased energy of interaction between γ- and β-subunits which was correlated to inefficient coupling between catalysis and transport. Based on these results and the X-ray crystallographic structure of bovine F₁-ATPase γM23K is believed to form an ionized hydrogen bond with βGlu-381 in the conserved β³⁸⁰DELSEED³⁸⁶ segment. In this report, we further test the role of γ-β-subunit interactions by introducing a series of substitutions for βGlu-381 and γArg-242, the residue which forms a hydrogen bond with βGlu-381 in the wild-type enzyme. βE381A, D, and Q were able to restore efficient coupling when coexpressed with γM23K. All three mutations reversed the increased transition state thermodynamic parameters for steady state ATP hydrolysis caused by γM23K. βE381K by itself caused inefficient coupling, but opposite from the effect of γM23K, the transition state thermodynamic parameters were lower than wild-type. These results suggest that the βE381K mutation perturbs the γ-β-subunit interaction and the local conformation of the β³⁸⁰DELSEED³⁸⁶ segment in a specific way that disrupts the communication of coupling information between transport and catalysis. βE381A, L, K, and R, and γR242L and E mutations perturbed enzyme assembly and stability to varying degrees. These results provide functional evidence that the β³⁸⁰DELSEED³⁸⁶ segment and its interactions with the γ-subunit are involved in the mechanism of coupling.