Fig. 6.

Electrostatic analysis of residues affecting Cl⁻ binding in SY and EC. a Static field contribution for each residue in SY (green) and EC (red) for a Cl⁻ ion bound to the central site. Deflections represent stabilizing (downward) or destabilizing (upward) energies for Cl⁻ binding. Residues showing significant differences between SY and EC are highlighted. b. Single subunit of SY viewed from the dimer interface, with helices H, I, P and Q removed for visualization of the Cl⁻ binding pathway. Residues near the central site (Y437, S103) and the external gate (E144) are shown. Residues with significant differences in electrostatics between SY and EC are highlighted in yellow, and the two residues (F143, D309) adjacent to the external site (blue ends of helices) are highlighted in red.