The sequential movements of positively charged residues (red spheres) upon depolarization. The highly conserved hydrophobic residue (F233) in the gating charge transfer center (formed by F233, E236, and D259) is shown as a green sphere. The other key negatively charged residues (E183, E226, E236, and D259) are shown as blue spheres. The gating transitions are associated with the predominant translational/rotational movements of the S4 helix along the relatively fixed S3 helix, sliding around 13 Å normal to membrane.