Figure 4

(a) Effect of ampicillin binding on the ion current in simulations under voltage. The asymmetric flux of Cl⁻ (green), Na⁺ ions (purple) and electro-osmotic flow of water molecules (blue) across the eyelet at negative and positive voltages is shown. Positive values of flux account for permeations from the extracellular compartment to the periplasmic compartment. Representative modes of ampicillin binding at positive (b) and negative voltages (C). The L3 loop of PorB is represented as blue cartoon and sticks and the initial and final structures of ampicillin are depicted as grey and orange sticks, respectively. (d,e,f,g) Overlay of ion positions (green spheres, Cl⁻; purple spheres, Na⁺) from 40 snapshots taken from the last 200 ns of simulation of bound ampicillin within PorB at (d) ~+400 mV, (e) ~−400 mV, (f) ~+125 mV and (g) ~−125 mV. Ion permeation is blocked at positive voltages, while anions can pass the PorB eyelet at negative voltages, leading to the asymmetric current-voltage behaviour.