FIGURE 3.

Hexameric model of activated Spa47. A, Spa47 modeled as an activated homohexamer, based on the F₁ ATP synthase structure. Each of the Spa47 monomer subunits are colored independently. B, surface representation of the hexameric model shown in top view and at a 90° rotation. Each of the six nucleotide-binding regions within the hexamer are located at a separate protomer interface with one example outlined. A closer view of the Spa47 active site looking from within the hexamer pore shows the conserved active site Lys¹⁶⁵ and Glu¹⁸⁸ side chains from one protomer (gray) and an arginine from the adjacent protomer (blue) in relation to the bound ATP homolog (AMPPNP) modeled from its location in the F₁ ATP synthase structure.