Subunit epsilon of the Escherichia coli ATP synthase: novel insights into structure and function by analysis of thirteen mutant forms.

Structural models of subunit epsilon of the ATP synthase from Escherichia coli have been determined recently by NMR [Wilkens et al. (1995) Nat. Struct. Biol. 2, 961-967] and by X-ray crystallography [Uhlin et al. (1997) Structure 5, 1219-1230], revealing a two-domain protein. In this study, six new epsilon mutants were constructed and analyzed: Y63A, D81A, T82A, and three truncated mutants, tr80(S), tr94(LAS), and tr117(AS). Seven mutants constructed previously were also analyzed: E31A, E59A, S65A, E70A, T77A, R58A, and D81A/R85A. Subunits were purified by isoelectric focusing from extracts of cells that overproduced these 13 mutants. F1 was prepared lacking subunit epsilon by immobilized-Ni affinity chromatography. Three mutants, E70A, S65A, and E31A, showed somewhat higher affinities and extents of inhibition than the wild type. Three mutants, T82A, R85A, and tr94(LAS), showed both lower affinities and extents of inhibition, over the concentration range tested. Two showed no inhibition, D81A and tr80(S). The others, T77A, Y63A, E59A, and tr117(AS), showed lower affinities than wild type, but the extents of inhibition were nearly normal. Results indicate that the C-terminal domain of subunit epsilon contributes to inhibition of ATP hydrolysis, but it is not necessary for ATP-driven proton translocation. Interactions with subunit gamma are likely to involve a surface containing residues S65, E70, T77, D81, and T82, while residues R85 and Y63 are likely to be important in the conformation of subunit epsilon.