Modulation of coupling in the Escherichia coli ATP synthase by ADP and P: Role of the ε subunit C-terminal domain.

The ε-subunit of ATP-synthase is an endogenous inhibitor of the hydrolysis activity of the complex and its α-helical C-terminal domain (εCTD) undergoes drastic changes among at least two different conformations. Even though this domain is not essential for ATP synthesis activity, there is evidence for its involvement in the coupling mechanism of the pump. Recently, it was proposed that coupling of the ATP synthase can vary as a function of ADP and P concentration. In the present work, we have explored the possible role of the εCTD in this ADP- and P-dependent coupling, by examining an εCTD-lacking mutant of Escherichia coli. We show that the loss of P-dependent coupling can be observed also in the εCTD-less mutant, but the effects of P on both proton pumping and ATP hydrolysis were much weaker in the mutant than in the wild-type. We also show that the εCTD strongly influences the binding of ADP to a very tight binding site (half-maximal effect≈1nM); binding at this site induces higher coupling in EFF and increases responses to P. It is proposed that one physiological role of the εCTD is to regulate the kinetics and affinity of ADP/P binding, promoting ADP/P-dependent coupling.