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(2P)4.1 towards lipids remains poorly understood. Here we show the two isoforms of K(2P)4.1 have distinct binding preferences for lipids dependent on acyl chain length and position on the glycerol backbone. Unexpectedly, the channel can also discriminate the fatty acid linkage at the sn-1 position. Of the 33 lipids interrogated using native mass spectrometry, phosphatidic acid (PA) had the lowest equilibrium dissociation constants for both isoforms of K(2P)4.1. Liposome potassium flux assays with K(2P)4.1 reconstituted in defined lipid environments show that those containing PA activate the channel in a dose-dependent fashion. Our results begin to define the molecular requirements for the specific binding of lipids to K(2P)4.1.