Fig. 4. The activated ion pore.

(A) Ion pore in the activated conformation. The solvent-accessible surface of the pore (wheat color) is depicted, showing the side entryways connecting it with the outside solution. Two subunits of the TMD are shown as ribbons (TM1 helices are red; TM2 helices are blue). Residues that line the walls of the pore are displayed as sticks and are labeled. Boxed labels indicate residues that were accessible to MTSES in activated channels and inaccessible in resting channels (Fig. 5). (B) TMD of the resting conformation, depicted as in (A). Narrow dimensions occlude solvent. Amino acids from (A) that form the walls of the activated pore are shown. (C and D) Close-up views of a side entryway in the activated conformation, showing cartoon (C) and surface-filling (D) representations. The perspective is of the entryway closest to the viewer from (A). In (C), amino acids surrounding the entryway are shown as sticks and the ion pore is depicted as in (A). In (D), the electrostatic surface is shown (red, −5 kT e⁻¹; blue, +5 kT e⁻¹), with the central white region indicating the opening of the entryway.