LAUSR

Cation–chloride cotransporters (CCCs) mediate the electroneutral transport of chloride, potassium and/or sodium across the membrane. They have critical roles in regulating cell volume, controlling ion absorption and secretion across epithelia, and maintaining intracellular chloride homeostasis. These transporters are primary targets for some of the most commonly prescribed drugs. Here we determined the cryo-electron microscopy structure of the Na–K–Cl cotransporter NKCC1, an extensively studied member of the CCC family, from Danio rerio. 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 reveal 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 CCCs and interpreting disease-related mutations.The cryo-EM structure of the zebrafish cation–chloride cotransporter NKCC1 reveals the domain organization, ion translocation pathway, ion-binding sites and key residues for binding activity, providing insights into the activity of this family of transporter proteins with key roles in physiology.