Structural characterization of the interaction of the δ and α subunits of the Escherichia coli F1F0-ATP synthase by NMR spectroscopy

A critical point of interaction between F-1 and F-0 in the bacterial F1F0-ATP synthase is formed by the alpha and delta subunits. Previous work has shown that the N-terminal domain (residues 3-105) of the 6 subunit forms a 6 alpha-helix bundle [Wilkens, S., Dunn, S. D., Chandler, J., Dahlquist, F. W., and Capaldi, R. A. (1997) Nat. Struct. Biol. 4, 198-201] and that the majority of the binding energy between delta and F, is provided by the interaction between the N-terminal 22 residues of the alpha- and N-terminal domain of the delta subunit [Weber, J., Muharemagic, A., Wilke-Mounts, S., and Senior, A. E. (2003) J. Biol. Chem. 278, 13623-136261. We have now analyzed a 1:1 complex of the delta-subunit N-terminal domain and a peptide comprising the N-terminal 22 residues of the alpha subunit by heteronuclear protein NMR spectroscopy. A comparison of the chemical-shift values of delta-subunit residues with and without a N-terminal peptide bound indicates that the binding interface on the N-terminal domain of the 6 subunit is formed by cc helices I and V. NOE cross-peak patterns in 2D C-12/C-12-filtered NOESY spectra of the C-13-labeled delta-subunit N-terminal domain in complex with unlabeled peptide verify that residues 8-18 in the alpha-subunit N-terminal peptide are folded as an a helix when bound to 6 N-terminal domain. On the basis of intermolecular contacts observed in C-12/C-13-filtered NOESY experiments, we describe structural details of the interaction of the delta-subunit N-terminal domain with the alpha-subunit N-terminal alpha helix.