Fig 1. Simulation system of the sodium channel Na_vAb embedded in a lipid bilayer.

For clarity, the voltage sensor domains are not shown; only two monomers, a few ions, and a thin layer of water are shown. The right panel depicts the selectivity filter lined by the amino acids TLESW. The green dots represent z-coordinates along the central axis, whose arrow indicates the inward direction. The distance of 8 Å between the oxygen atoms of opposite hydroxyl groups of S178 is greater than the smallest width of the selectivity filter, which is 4.6 Å.