Selective regulation of human TRAAK channels by biologically active phospholipids.

TRAAK is an ion channel from the two-pore domain potassium (K) 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 K4.1 toward lipids remains poorly understood. Here we show the two isoforms of K4.1 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 SN position. Of the 33 lipids interrogated using native mass spectrometry, phosphatidic acid had the lowest equilibrium dissociation constants for both isoforms of K4.1. Liposome potassium flux assays with K4.1 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 K4.1.