Fig. 5. Electrostatic contribution in peptide binding and translocation through gpPorA. (a) Electrical recordings showing R9 interaction with single gpPorA (100 μM, cis) at −10 mV, −20 mV and −30 mV in 1 M KCl. (b) Electrical recordings showing R9 interaction with single gpPorA (0.5 μM, cis) at −5 mV and −15 mV (pH 4.5) and −15 mV (pH 7.4) in 0.15 M KCl. (c) Model showing the pPorA charge pattern with D9. Electrical recordings showing anionic D9 interaction with gpPorA (100 μM, cis) at +10 mV and +50 mV. Inset, recording at the expanded time scale and the corresponding τ_off dwell time histogram. Electrolyte: 0.15 M KCl/1 M KCl, 10 mM HEPES, pH 7.4 and citrate buffer, pH 4.5. The current signals (a and c) were filtered at 10 kHz and sampled at 50 kHz and (b) were digitally filtered at 1 kHz and 2 kHz using an 8-pole Bessel digital filter.