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Abstract The Na+-Cl− cotransporter (NCC) drives salt reabsorption in the kidney and plays a decisive role in balancing electrolytes and blood pressure. Thiazide and thiazide-like diuretics inhibit NCC-mediated renal salt retention and have been cornerstones for treating hypertension and edema since the 1950s. Here we determine NCC co-structures individually complexed with the thiazide drug hydrochlorothiazide, and two thiazide-like drugs chlorthalidone and indapamide, revealing that they fit into an orthosteric site and occlude the NCC ion translocation pathway. Aberrant NCC activation by the WNKs-SPAK kinase cascade underlies Familial Hyperkalemic Hypertension, but it remains unknown whether/how phosphorylation transforms the NCC structure to accelerate ion translocation. We show that an intracellular amino-terminal motif of NCC, once phosphorylated, associates with the carboxyl-terminal domain, and together, they interact with the transmembrane domain. These interactions suggest a phosphorylation-dependent allosteric network that directly influences NCC ion translocation.

Loop diuretics including bumetanide inhibit Na+-K+-Cl−-cotransporters (NKCCs) and are used for the treatment of edema and hypertension. Here, Zhao et. al. report structures of NKCC1 with bumetanide bound, revealing its mechanism of action that would facilitate design of novel diuretics.

Zhang et al. present the cryo-electron microscopy structures of the two neuronal cation-chloride cotransporters human NKCC1 and mouse KCC2, identifying their essential residues for ion transport. This study proposes mechanisms by which phosphorylation regulates the activity of these cation-chloride cotransporters.

The Na-K-Cl cotransporter (NKCC) couples the movement of Na(+), K(+), and Cl(-) ions across the plasma membrane of most animal cells and thus plays a central role in cellular homeostasis and human physiology. In order to study the structure, function, and regulation of NKCC1 we have engineered a synthetic cDNA encoding the transporter with 30 unique silent restriction sites throughout the open reading frame, and with N-terminal 3xFlag and YFP tags. We show that the novel cDNA is appropriately expressed in HEK-293 cells and that the YFP-tag does not alter the transport function of the protein. Utilizing the Cl(-) -sensing capability of YFP, we demonstrate a sensitive assay of Na-K-Cl cotransport activity that measures normal cotransport activity in a fully activated transporter. In addition we present three newly developed epitope tags for NKCC1 all of which can be detected from outside of the cell, one of which is very efficiently delivered to the plasma membrane. Finally, we have characterized cysteine mutants of NKCC1 and found that whereas many useful combinations of cysteine mutations are tolerated by the biosynthetic machinery, the fully "cys-less" NKCC1 is retained in the endoplasmic reticulum. Together these advances are expected to greatly assist future studies of NKCC1.