Selective regulation of human TRAAK channels by biologically active phospholipids

Abstract

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.

Insights into the Role of Membrane Lipids in the Structure, Function and Regulation of Integral Membrane Proteins

“…Cholesterol Activity regulation [8,9] Activity and changes in conformation [10], Modulation of substrate binding affinity [11] Channel inhibition [12] Activation [13], Signalling [14,15], Stability [16,17], Allosteric regulation [18], Lower affinity ligand binding [17], Oligomerisation [19][20][21][22][23] PA Activity [24] Stabilisation [25] PE Dimer formation and function [26], Dimer formation [27], conformer stability [28] Conformer stabilisation and channel desensitisation [29] Agonist and antagonist binding affinities [30], Increase G protein coupling [31,32] Protein assembly [33] PC Dimerisation [34], β-arrestin interaction and function [35], Increase G protein coupling [31] PG Oligomerisation and function [36] Conformer stabilisation and channel desensitisation [37] Increase G protein coupling [30,38], Active conformer stability [39], β-arrestin interaction and function [35], Decrease G protein coupling [31] PS Dimer formation [27], Stabilisation [25], Dimerisation [34], Decrease G protein coupling [31] PI Dimer formation and function…”

“…A recent study on the two-protein domain potassium (K 2P ) channel, TRAAK, using a combination of native MS and liposome-based potassium efflux assay, allowed a detailed analysis of the lipids involved in the regulation of channel activity. The results revealed that TRAAK was activated by high affinity binding of phosphatidic acid (PA) [24].…”

Assessing the Role of Lipids in the Molecular Mechanism of Membrane Proteins

“…This suggests that CsA binding primes the transporter for subsequent lipid binding, either through a conformational change or adaptation of the ligand pocket. Such a method was used successfully on GPCRs [ 132 ], channels [ 133 , 134 , 135 , 136 ], transporters [ 131 , 137 , 138 , 139 ] and other IMPs [ 140 ], highlighting the role of specific lipid species in allosteric coupling.…”

From Bench to Biomolecular Simulation: Phospholipid Modulation of Potassium Channels

“…These lipids have been previously suggested to activate multiple K + channels such as K ir , TREK1 and TRAAK. 79 , 80 , 81 …”

“… 121 , 122 Early nMS work on ion channel lipid interactions focused on the effect of lipids (and other effects) on the stoichiometry of the mechanosensitive channel of large conductance (MscL) in different bacteria. 121 Furthermore, nMS has been applied to characterise the selectivity of lipid binding to the isoforms of the TRAAK channel 80 and to K ir 3.2 where PIP 2 was shown to bind selectively and single mutations influence the affinities and specificity. 124 A more comprehensive review on characterising protein-lipid interactions through nMS can be found in.…”