@article{Xie2026, 
author = {Yuan Xie and Binming Han and Xin Tao and Fangjun Song and Cheng Zhao and Eric Delpire and Jingyuan Li and Shan Wu and Jiangtao Guo},
title = {Structural basis for the ion selectivity of potassium-chloride cotransporter KCC4 revealed by cryo-EM titration},
year = {2026},
journal = {Biophysics Reports},
volume = {12},
number = {3},
pages = {193-206},
keywords = {KCC4, Cryo-EM titration, Ions selectivity, Molecular dynamic simulation, Ions cotransport},
url = {https://www.sciopen.com/article/10.52601/bpr.2025.240057},
doi = {10.52601/bpr.2025.240057},
abstract = {Potassium-chloride cotransporters KCCs mediate the coupled, electroneutral cotransport of K+ and Cl− across the membrane and are involved in important physiological processes such as cell volume regulation and γ-aminobutyric acid (GABA) and glycine-mediated inhibitory neurotransmission. Although structures of KCCs have been reported, the identification of ions bound in KCCs awaits experimental studies. Here using the cryo-electron microscopy (cryo-EM) titration methods, we present six structures of human KCC4 in different ion conditions at 2.38–2.58 Å resolutions. These structures, along with molecular dynamic simulations, allow us to assign one K+ and two Cl− ions in the substrate-binding pocket. The K+ at S1 and Cl− at the S2 site are tightly coupled in the binding and dissociation, suggesting that the Cl− at S2 but not at S3 is the cotransported one. The S1 site provides coordination that largely matches the K+ dehydration radius and therefore displays higher selectivity to K+ over Na+. This study establishes the structural basis for the K+ selectivity of KCCs by the cryo-EM titration.}
}