Fig. 6.

Coordination of Na⁺ at the Na2 site in WT NIS and NIS mutants. (A–F) MD simulations were carried out with WT NIS or the indicated NIS mutants with the Na2, Na1, and I⁻ sites occupied. The residual activity of each NIS mutant is given in parentheses as a % of WT NIS activity. Ep and E, respectively, refer to the protonated and nonprotonated forms of glutamate. (G) Summary of the integrated frequencies and free energies of residues 0–3 Å from the Na⁺ at the Na2 site. (H) Summary of the integrated frequencies and free energies of residues 3–5 Å from the Na⁺ at the Na2 site.