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Potassium channels selectively conduct K(+), primarily to the exclusion of Na(+), despite the fact that both ions can bind within the selectivity filter. Here we perform crystallographic titration and single-channel electrophysiology to examine the competition of Na(+) and K(+) binding within the filter of two NaK channel mutants; one is the potassium-selective NaK2K mutant and the other is the non-selective NaK2CNG, a CNG channel pore mimic. With high-resolution structures of these engineered NaK channel constructs, we explicitly describe the changes in K(+) occupancy within the filter upon Na(+) competition by anomalous diffraction. Our results demonstrate that the non-selective NaK2CNG still retains a K(+)-selective site at equilibrium, whereas the NaK2K channel filter maintains two high-affinity K(+) sites. A double-barrier mechanism is proposed to explain K(+) channel selectivity at low K(+) concentrations.

Original publication




Journal article


Nature communications

Publication Date





1] Department of Physiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9040, USA [2].


Bacillus cereus, Bacillus subtilis, Escherichia coli, Potassium, Sodium, Bacterial Proteins, Potassium Channels, Liposomes, Crystallography, X-Ray, Electrophysiology, Ion Channel Gating, Binding Sites, Binding, Competitive, Protein Conformation, Mutation