Three-dimensional structure of zfV2. (A and B) Side and top views of zfV2 (PDB ID code 4bum) illustrated using Pymol. Pink is the sufficient segment, and yellow (sticks) is the necessary residues, including S156 and D158. (C, Right) Side view of the segment containing amino acids S156 and D158 (yellow sticks) in zfV2 vs. the relevant residues in mV1 (N156 and E158, orange sticks). Residues 111–167 in zfV2 (blue) and mV1 (PDB ID code: 3emn, orange) were superimposed. (C, Left) Interior view of the channels showing the residues that are within a distance of 4 Å from either S156 or D158 in zfV2 (sticks with carbon colored blue) or N156 or E158 in V1 (sticks with carbon colored orange). In sticks, oxygen is red and nitrogen is green. Adjacent residues have also been marked in the sequences of zfV2 (blue) and mV1 (orange).