Fig. 5.
NIS model based on the vSGLT structure. The homology model, including NIS residues 50 to 476, was generated as described in SI Text. (A) Overall structure. TMS III–VI2–5 are colored magenta and TMS VII–XI6–10 orange. G93 (red) abuts the indole ring of W255 (olive). The rest of the model is colored green. (B) Close-up of the NIS cavity depicting G93 and W255 opposite the unwound portion of TMS VII6. N97 and Y259 also face each other at the bottom end of the cavity. M90 forms part of the upper roof of the cavity. Transition between two conformations of NIS: (C) Superposition of the inwardly open and outwardly open conformations showing the movement of the hairpins and the connecting residues. The inwardly open conformation (vSGLT-like) is colored light green and the outwardly open conformation (LeuT-like) red. The green arrow shows the position of TMS III2 in the inwardly open conformation and the red arrow the position of the outwardly open conformation. The black arrow indicates the point around which the connecting short helix pivots to allow the rotation of the two helical hairpins. (D) Close-up of boxed region in C. (E) Schematic representation of D; TMS III and IV2–3 are depicted as cylinders, the short helix as a rectangle, the unstructured connections between TMS III and IV2–3, and the rectangle as rods. Color scheme as in C and D.