Structure of the F1-binding Domain of the Stator of Bovine F1Fo-ATPase and How it Binds an α-Subunit

The peripheral stalk of ATP synthase holds the α3β3 catalytic subcomplex stationary against the torque of the rotating central stalk. In bovine mitochondria, the N-terminal domain of the oligomycin sensitivity conferral protein (OSCP-NT; residues 1–120) anchors one end of the peripheral stalk to the N-terminal tails of one or more α-subunits of the F1 subcomplex. Here we present the solution structure of OSCP-NT and an NMR titration study of its interaction with peptides representing N-terminal tails of F1 α-subunits. The structure comprises a bundle of six α-helices, and its interaction site contains adjoining hydrophobic surfaces of helices 1 and 5; residues in the region 1–8 of the α-subunit are essential for the interaction. The OSCP-NT is similar to the N-terminal domain of the δ-subunit from Escherichia coli ATP synthase (δ-NT), except that their surface charges differ (basic and acidic, respectively). As the charges of the adjacent crown regions in their α3β3 complexes are similar, the OSCP-NT and δ-NT probably do not contact the crowns extensively. The N-terminal tails of α-subunit tails are probably α-helical, and so this interface, which is essential for the rotary mechanism of the enzyme, appears to consist of helix–helix interactions.