Structural basis for human NKCC1 inhibition by loop diuretic drugs

Area of Science:

• Biochemistry and structural biology
• Cellular physiology
• Pharmacology

Background:

• Na+-K+-Cl- cotransporters (NKCCs) are vital for epithelial chloride secretion, cell volume homeostasis, and renal salt reabsorption.
• Loop diuretics (furosemide, bumetanide, torsemide) inhibit NKCC1 and NKCC2, serving as primary treatments for edema and hypertension.
• WNK kinases activate NKCC1 in response to hypertonic stress, but the mechanism of phosphorylation-accelerated ion transport is unknown.

Purpose of the Study:

• To elucidate the structural mechanisms by which phosphorylation activates NKCC1.
• To understand how loop diuretics interact with and inhibit phospho-activated NKCC1.

Main Methods:

• Co-structure determination of phospho-activated NKCC1 bound to loop diuretics.
• Structural analysis of drug-protein interactions and conformational changes.

Main Results:

• Furosemide and bumetanide coordinate K+ using a carboxyl group, while torsemide expels K+ from the binding site.
• Phosphorylated NKCC1 undergoes an N-terminal to C-terminal domain interaction, facilitating ion translocation.
• Detailed structures reveal distinct binding modes of different loop diuretics.

Conclusions:

• Phosphorylation induces conformational changes in NKCC1, enabling rapid ion transport.
• Loop diuretics inhibit NKCC1 through specific interactions at the ion-binding site, with distinct mechanisms for different drugs.
• These findings provide a molecular basis for NKCC1 function and diuretic inhibition, aiding in drug development.