Selective regulation of human TRAAK channels by biologically active phospholipids

TRAAK is an ion channel from the two-pore domain potassium (K_2P) channel family with roles in maintaining the resting membrane potential and fast action potential conduction. Regulated by a wide range of physical and chemical stimuli, the affinity and selectivity of K_2P4.1 toward lipids remains poorly understood. Here we show the two isoforms of K_2P4.1 have distinct binding preferences for lipids dependent on acyl chain length and position on the glycerol backbone. The channel can also discriminate the fatty acid linkage at the SN₁ position. Of the 33 lipids interrogated using native mass spectrometry, phosphatidic acid had the lowest equilibrium dissociation constants for both isoforms of K_2P4.1. Liposome potassium flux assays with K_2P4.1 reconstituted in defined lipid environments show that those containing phosphatidic acid activate the channel in a dose-dependent fashion. Our results begin to define the molecular requirements for the specific binding of lipids to K_2P4.1.