The mechanism of anion selectivity in the human kidney chloride channels ClC-Ka and ClC-Kb is unknown. However, it has been thought to be very similar to that of other channels and antiporters of the CLC protein family, and to rely on anions interacting with a conserved Ser residue (Sercen) at the center of three anion binding sites in the permeation pathway Scen. In both CLC channels and antiporters, mutations of Sercen alter the anion selectivity. Structurally, the side chain of Sercen of CLC channels and antiporters typically projects into the pore and coordinates the anion bound at Scen.
