BPS2026 - A shared cavity site for lipid and small molecule block of the two-pore domain K+ channel TASK-2

TASK-2 is a pH-sensitive two-pore domain K + channel that has been shown to play physiological roles in ionic homeostasis, volume regulation, and regulation of respiratory rate. We report that at acidic pH, TASK-2 retains an extremely low open probability mediated by a previously unresolved intracellular gate and inner leaflet acyl chains that can enter an intracellular vestibule to occlude conduction. Loss of lipid-inhibition of TASK-2 results in a pronounced gain-of-function phenotype characterized by a dramatic increase in open probability. We demonstrate that mutation of an internal proton sensor K245 results in a surprising loss-of-function due to a unique function of this residue in both stabilizing a closed internal gate at acidic pH and disfavoring lipid occlusion at alkaline pH. Additionally, we show that the anesthetic bupivacaine binds within the inner channel vestibule below the selectivity filter to block ion conduction. These results highlight the importance of the internal channel vestibule to normal channel function and demonstrate how this region may be utilized for the development of potential channel modulators.