SOLUTION STRUCTURE OF THE EPSILON-SUBUNIT OF THE F-1-ATPASE FROM ESCHERICHIA-COLI AND INTERACTIONS OF THIS SUBUNIT WITH BETA-SUBUNITS IN THE COMPLEX

The solution structure of the epsilon subunit of the Escherichia coli F-1-ATPase has been determined by NMR spectroscopy. This subunit has a two-domain structure with an N-terminal 10-stranded beta sandwich and a C-terminal antiparallel two alpha-helix hairpin, as described previ ously (Wilkens, S., Dahlquist, F. W., McIntosh, L. P., Donaldson, L, W ,, and Capaldi, R. A. (1995) Nat, Struct. Biol. 2, 961-967). New data show that the two domains interact in solution in an interface formed by beta strand 7 and the very C-terminal alpha-helix. This interface i nvolves only hydrophobic interactions. The dynamics of the epsilon sub unit in solution were examined. The two domains are relatively tightly associated with little or no flexibility relative to one another. The epsilon subunit can exist in two states in the ECF1F0 complex dependi ng on whether ATP or ADP occupies catalytic sites. Proteolysis of the epsilon subunit in solution and when bound to the core F-1 complex ind icates that the conformation of the polypeptide in solution closely re sembles the conformation of epsilon when bound to the F, in the ADP st ate. Chemical and photo-cross-linking show that the epsilon subunit sp ans and interacts with two beta subunits in the ADP state. These inter actions are disrupted on binding of ATP + Mg2+, as is the interaction between the N- and C-terminal domains of the epsilon subunit.