STRUCTURAL FEATURES OF THE EPSILON-SUBUNIT OF THE ESCHERICHIA-COLI ATP SYNTHASE DETERMINED BY NMR-SPECTROSCOPY

The tertiary fold of the epsilon subunit of the Escherichia coli F1F0 ATPsynthase (ECF(1)F(0)) has been determined by two- and three-dimensional heteronuclear (C-13, N-15) NMR spectroscopy. The epsilon subunit exhibits a distinct two domain structure, with the N-terminal 84 residues of the protein forming a 10-stranded beta-structure, and with the C-terminal 48 amino acids arranged as two alpha-helices running antiparallel to one another (two helix hairpin). The beta-domain folds as a beta-sandwich with a hydrophobic interior between the two layers of the sandwich. The C-terminal two-helix hairpin folds back to the N-terminal domain and interacts with one side of the beta-domain. The arrangement of the epsilon subunit in the intact F1F0 ATP synthase involves interaction of the two helix hairpin with the F-1 part, and binding of the open side of the beta-sandwich to the c subunits of the membrane-embedded F-0 part.