The shapes and radius of the ion pathway of NavAb N49K, S178T NK , S178A NK , and S178G NK mutants. (A–D) Horizontal view of the ion pathway of NavAb N49K, S178TNK, S178ANK, and S178GNK mutants depicted by program hole. Background (BG) indicates N49K mutant without the Ser178 mutation. The carbon atoms of NavAb N49K, S178TNK, S178ANK, and S178GNK mutants are colored cyan, magenta, green, and yellow, respectively. (E) The pore radius of NavAb N49K, S178TNK, S178ANK, and S178GNK mutants. The baseline of the z axis is set to the z-coordinate of the main-chain carbonyl oxygen atoms of the 178th residue. The extracellular direction is plotted as plus, and the cytosolic direction as minus.