Crosstalk along the stalk: Dynamics of the interaction of subunits B and F in the A1AO ATP synthase of methanosarcina mazei Gö1

Abstract

The mechanism of coupling of ion pumping in the membrane-bound A O sector with ATP synthesis in the A3B3 headpiece of the A1 sector in the A1AO ATP synthase is a puzzle. Previously, crosstalk between the stalk and nucleotide-binding subunits FMm and BMm of the Methanosarcina mazei Gö1 A-ATP synthase has been observed by nucleotide-dependent cross-link formation of both subunits inside the enzyme. The recently determined NMR solution structure of FMm depicts the protein as a two-domain structure, with a well-folded N-terminus having 78 residues and a flexible C-terminal part (residues 79-101), proposed to become structured after binding to its partner, BMm. Here, we detail the crucial interactions between subunits BMm and FMm by determining the NMR structure of the very C-terminus of FMm, consisting of 20 residues and hereafter termed FMm(81-101), and performing molecular dynamics simulations on the resulting structure. These data demonstrate that the flexibility of the C-terminus enables FMm to switch between an elongated and retracted state. Docking and MD in conjunction with previously conducted and published NMR results, biochemical cross-linking, and fluorescence spectroscopy data were used to reconstruct a model of a B Mm-FMm assembly. The model of the BMm-F Mm complex shows the detailed interactions of helices 1 and 2 of the C-terminal domain of BMm with the C-terminal residues of F Mm. Movements of both helices of BMm accommodate the incoming C-terminus of FMm and connect the events of ion pumping and nucleotide binding in the A1AO ATP synthase. © 2010 American Chemical Society.