The Solute Carrier Family 12 (SLC12) encodes electroneutral cation-chloride cotransporters (CCCs) that are fundamental in cell volume regulation and chloride homeostasis. Dysfunction of CCCs engenders abnormality in renal function and neuro-system development. Here we presented structure of the full length human potassium-chloride co-transporter 2 (KCC2) and 3 (KCC3), the KCC3 mutants in phosphorylation mimic (P-mimic) and dephosphorylation mimic (DP-mimic) status, and KCC3 in complex with [(DihydroIndenyl)Oxy] Alkanoic acid (DIOA), a specific inhibitor of KCCs, at resolution of 2.7 Å - 3.6 Å. A small N-terminal loop is bound at the intracellular vestibule of the transport path, arresting the transporter in an auto-inhibition state. The C-terminal domain (CTD) of KCCs is structure-solved for the first time, revealing two conserved phosphorylation harboring segments (PHSs), which exhibit different conformation between P-mimic and DP-mimic mutants, explaining the inhibitory effect of phosphorylation. DIOA is located in between the two transmembrane domains, tightly bound to the loop between TM10 and TM11, locking the transporter in inward-facing conformation. Together, our study makes important steps in understanding the sophisticated regulation mechanisms of KCCs, with prospect for the specific drug development.

Molecular basis for regulation of human potassium chloride cotransporters