Figure 5

(a,b) Pathways of K⁺ and Cl⁻ ions in the MtrE channel (depicted as ion density) and average water density in the channel during simulations at (a) +100 mV and (b) −100 mV. The panels show the extracellular side of MtrE at the top and the periplasmic gate at the bottom of each figure. Under both conditions, a thinning out of the ion density at the periplasmic gate can be observed, especially for K⁺ ions. (c) Superposition of all K⁺ (orange) and Cl⁻ (green) ions during 250 ns (1 frame every 2.5 ns, 100 total frames) at +100 mV clearly shows this constriction of the ion pathways within the gating region, representing the major bottleneck for ion permeation.