Fig. 2 | Nature Communications

Fig. 2

From: Electro-osmotic capture and ionic discrimination of peptide and protein biomarkers with FraC nanopores

Fig. 2

Ion selectivity and electrostatic distribution of WtFraC and ReFraC. a Determination of the reversal potential shows that WtFraC and ReFraC are, respectively, cation- and anion-selective, as expected from the electrostatic potentials at their constrictions. All reversal potentials were measured under asymmetric salt conditions (467 mM KCl in trans and 1960 mM KCl in cis) and the ion selectivity determined using the Goldman–Hodgkin–Katz equation (Eq. 1 in the main text). The buffer contained 15 mM Tris base at pH 7.5 and 100 mM sodium citrate at pH 4.5. b The averaged simulated electrostatic potentials reveal the negatively and positively charged constrictions of WtFraC and ReFraC, respectively. While for ReFraC lowering of the pH from 7.5 to 4.5 only had a small effect on the electrostatic potential, for WtFraC the peak value at the center of the constriction dropped by 37%. All simulations were performed using APBS75 at 1 M KCl, with the partial charge of each titratable residue adjusted according to their average protonation states with a modified version of the PDB2PQR software72. Residue pKa values were estimated using PROPKA78, 79. Detailed experiment procedures are given in Methods section. The envelopes behind every current–voltage curve represent their respective standard deviations obtained from three repeats

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