Structure and Mechanism of the Cation–chloride Cotransporter NKCC1

Abstract

Cation-chloride cotransporters (CCCs) mediate the electroneutral transport of chloride, potassium, and/or sodium across the membrane. They play critical roles in regulating cell volume, controlling ion absorption and secretion across epithelia, and maintaining intracellular chloride homeostasis. These transporters are the primary targets for some of the most commonly prescribed drugs in clinic. Here, we determined the cryo-EM structure of a Na-K-Cl cotransporter NKCC1, an extensively-studied member of the CCC transporters. The structure defines the architecture of this protein family and reveals how cytosolic and transmembrane domains are strategically positioned for communication. Structural analyses, functional characterizations, and computational studies uncover the ion translocation pathway, ion-binding sites, and key residues for transport activity. These results provide insights into ion selectivity, coupling, and translocation, and establish a framework for understanding the physiological functions of CCC transporters and interpreting disease-related mutations.