The site 4 interaction surface of the dodecamer complex. Dodecamer assembly occurs through the site 4 interaction surface at the hexamer:hexamer interface. (A) View of the site 4 interface, demonstrating that the residues are predominantly from βc domain 4 (green), but include some from GMRα domain 2 (red). Coloring as in Figure 1. (B) Comparison of the sequence of the βc site 4 region from different species. The blue bars denote the region located at the site 4 interface.