Structural requirements of membrane phospholipids for M-type potassium channel activation and binding.
Journal of Biological Chemistry
10001 - 10012.
M-channels are voltage-gated potassium channels that regulate cell excitability. They are heterotetrameric assemblies of Kv7.2 and Kv7.3 subunits. Their opening requires the presence of the membrane phospholipid phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)). However, the specificity of PI(4,5)P(2) as a binding and activating ligand is unknown. Here, we tested the ability of different phosphoinositides and lipid phosphates to activate or bind to M-channel proteins. Activation of functional channels was measured in membrane patches isolated from cells coexpressing Kv7.2 and Kv7.3 subunits. Channels were activated to similar extents (maximum open probability of ∼0.8 at 0 mV) by 0.1-300 μM dioctanoyl homologs of the three endogenous phosphoinositides, PI(4)P, PI(4,5)P(2), and PI(3,4,5)P(3), with sensitivity increasing with increasing numbers of phosphates. Non-acylated inositol phosphates had no effect up to 100 μM. Channels were also activated with increasing efficacy by 1-300 μM concentrations of the monoacyl monophosphates fingolimod phosphate, sphingosine 1-phosphate, and lysophosphatidic acid but not by phosphate-free fingolimod or sphingosine or by phosphate-masked phosphatidylcholine or phosphatidylglycerol. An overlay assay confirmed that a fusion protein containing the full-length C terminus of Kv7.2 could bind to a broad range of phosphoinositides and phospholipids. A mutated Kv7.2 C-terminal construct with reduced sensitivity to PI(4,5)P showed significantly less binding to most polyphosphoinositides. We concluded that M-channels bind to, and are activated by, a wide range of lipid phosphates, with a minimum requirement for an acyl chain and a phosphate headgroup. In this, they more closely resemble inwardly rectifying Kir6.2 potassium channels than the more PI(4,5)P(2)-specific Kir2 channels. Notwithstanding, the data also support the view that the main endogenous activator of M-channels is PI(4,5)P(2).
|Title:||Structural requirements of membrane phospholipids for M-type potassium channel activation and binding.|
|Open access status:||An open access version is available from UCL Discovery|
|Additional information:||© 2012 by The American Society for Biochemistry and Molecular Biology, Inc. This is an Open Access article distributed under a Creative Commons Attribution-NonCommercial 3.0 Unported License, which allows noncommercial use, distribution, and reproduction in any medium, provided the original author and source are credited.|
|Keywords:||Animals, CHO Cells, Cricetinae, Cricetulus, Humans, KCNQ2 Potassium Channel, KCNQ3 Potassium Channel, Phosphatidylinositol 4,5-Diphosphate, Phosphatidylinositol Phosphates, Phospholipids, Potassium Channels, Inwardly Rectifying|
|UCL classification:||UCL > School of Life and Medical Sciences > Faculty of Life Sciences > Biosciences (Division of) > Neuroscience, Physiology and Pharmacology
UCL > School of Life and Medical Sciences > Faculty of Medical Sciences > Medicine (Division of)
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