Figure 2: Leu25 and ion-binding sites.

(a,b), The extracellular cavity and binding pockets for Leu25 and substrate in the Na⁺-free state (a, P2₁ form molecule B, this study), and the Na⁺- and substrate-bound outward-occluded state³ (b, PDB entry code 2A65). The Na⁺ ions are shown as green spheres, Glu290 and L-leucine at the binding site by cyan and yellow spheres for carbon, respectively. The conservation is coloured from low (cyan) to high (magenta) using ConSurf⁵⁵. (c) Na2 and Na1 sites in the outward-oriented Na⁺-free (pink, this study) and Na⁺-bound states with bound leucine substrate³ (grey, PDB entry code 2A65). Na⁺ binding and relocation of Leu25 to the substrate-binding site are mutually exclusive.