Charge delocalization upon chloride ion binding in ClC chloride ion channels/transporters

Density functional theory calculations were carried out employing a set of truncated model systems for the EcClC Cl− transport protein and mutants. Geometry optimizations implied a possible additional binding site near the residue R147. Analysis based on the Löwdin and Natural charge models showed that significant (about 30%) charges on the bound Cl− ions were smeared out among the solvation shells and the gating residue E148, whose delocalized pi bonds provide good accommodations for the transferred charges. The extensive anion-pi charge transfer along the Cl− translocation path might help to smooth/level the energy profiles for Cl− transport.