Fig. 5. Anion-backbone interaction along the permeation pathway in WT and M427µ bCLC-k.

A Single-occupancy PMF calculated along the ion permeation pathway for Cl⁻, Br⁻, I⁻, and NO₃⁻ in WT bCLC-k. The z positions for the ions are specified relative to S_ext (z = 0). The positions of S_ext, an intermediate binding region, and S_cen are indicated by the green, orange, and purple vertical dashed lines, respectively. PMFs are aligned by their energy in the bulk solution. B) Single-occupancy PMF calculated along the ion permeation pathway for Cl⁻, Br⁻, I⁻, and NO₃⁻ in the M427μ mutant of bCLC-k. The uncertainty error in (A) and (B) is calculated based on Monte Carlo bootstrapping and shown in shaded colors (almost unnoticeable). C The selectivity filter of bCLC-k along with the positions of all major binding sites (based on the PMFs, panels (A) and (B)) for different anions depicted in vdW for both WT and the M427μ mutant (Cl⁻ in white, Br⁻ in red, NO₃⁻ in blue, and I⁻ in yellow). The three dashed lines correspond to those drawn in panels (A) and (B). D Comparison of hydration patterns in the selectivity filter of WT and M427μ bCLC-k, highlighting the shift in the orientations of water molecules.