Solution structure of the ε subunit of the F1-ATPase from Escherichia coli and interactions of this subunit with β subunits in the complex

Abstract

The solution structure of the ε subunit of the Escherichia coli F1- ATPase has been determined by NMR spectroscopy. This subunit has a two- domain structure with an N-terminal 10-stranded β sandwich and a C-terminal antiparallel two α-helix hairpin, as described previously (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 β strand 7 and the very C- terminal α-helix. This interface involves only hydrophobic interactions. The dynamics of the ε subunit in solution were examined. The two domains are relatively tightly associated with little or no flexibility relative to one another. The ε subunit can exist in two states in the ECF1F0 complex depending on whether ATP or ADP occupies catalytic sites. Proteolysis of the subunit in solution and when bound to the core F1 complex indicates that the conformation of the polypeptide in solution closely resembles the conformation of ε when bound to the F1 in the ADP state. Chemical and photocross-linking show that the ε subunit spans and interacts with two β subunits in the ADP state. These interactions are disrupted on binding of ATP + Mg2+, as is the interaction between the N- and C-terminal domains of the ε subunit.