Cartoons view of the bovine F1-ATPase: α3, β3, γ, δ, ε. There are 6 nucleotide binding sites, one associated with each of the α and β subunits.
This shows one β subunit with a bound ADP. It has 3 domains: an all β-sheet domain at the top (N-terminus), an α/β domain in the middle, and an all α domain at the C-terminus. ADP binds to the center domain.
The nucleotide binding domain of the β subunit. The switch point occurs between the blue and green strands. Notice a loop from a β-strand that wraps around the phosphate of the ADP. This is the P-loop.
1e79 (PDB 147-360)
Gibbons, C., Montgomery, M. G., Leslie, A. G. W., Walker, J. E.: The Structure of the Central Stalk in Bovine Mitochondrial F1-ATPase at 2.4 A Resolution Nat.Struct.Biol. 7 pp. 1055 (2000) (PubMed)