Two Cl Ions and a Glu Compete for a Helix Cage in the CLC Proton/Cl− Antiporter

The ubiquitously expressed CLC chloride transporters are involved in a great variety of physiological functions. The CLC protein fold is shared by Cl− channels and 2Cl−:1H+ antiporters. The antiporters pump three charges per cycle across the membrane with two Cl ions moving in the opposite direction of one proton. Multiconformational continuum electrostatics was used to calculate the coupled thermodynamics of the protonation of the extracellular-facing gating Glu (Ex) and Cl− binding to the external (Sx) and central (Sc) sites in CLC-ec1, the Escherichia coli exchanger.

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