TY - JOUR TI - Cryo-EM structure of the potassium-chloride cotransporter KCC4 in lipid nanodiscs AU - Reid, Michelle S AU - Kern, David M AU - Brohawn, Stephen Graf A2 - Kühlbrandt, Werner A2 - Boudker, Olga A2 - Chen, Jue A2 - Padan, Etana VL - 9 PY - 2020 DA - 2020/04/14 SP - e52505 C1 - eLife 2020;9:e52505 DO - 10.7554/eLife.52505 UR - https://doi.org/10.7554/eLife.52505 AB - Cation-chloride-cotransporters (CCCs) catalyze transport of Cl- with K+ and/or Na+across cellular membranes. CCCs play roles in cellular volume regulation, neural development and function, audition, regulation of blood pressure, and renal function. CCCs are targets of clinically important drugs including loop diuretics and their disruption has been implicated in pathophysiology including epilepsy, hearing loss, and the genetic disorders Andermann, Gitelman, and Bartter syndromes. Here we present the structure of a CCC, the Mus musculus K+-Cl- cotransporter (KCC) KCC4, in lipid nanodiscs determined by cryo-EM. The structure, captured in an inside-open conformation, reveals the architecture of KCCs including an extracellular domain poised to regulate transport activity through an outer gate. We identify binding sites for substrate K+ and Cl- ions, demonstrate the importance of key coordinating residues for transporter activity, and provide a structural explanation for varied substrate specificity and ion transport ratio among CCCs. These results provide mechanistic insight into the function and regulation of a physiologically important transporter family. KW - ion transport KW - potassium chloride cotransporter KW - cryo-EM KW - nanodisc JF - eLife SN - 2050-084X PB - eLife Sciences Publications, Ltd ER -