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Proc Natl Acad Sci U S A. 2016 Apr 12;113(15):4194-9. doi: 10.1073/pnas.1522459113. Epub 2016 Mar 28.

Heterodimerization within the TREK channel subfamily produces a diverse family of highly regulated potassium channels.

Author information

1
Department of Molecular and Cell Biology and Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720;
2
Institute of Biology Valrose (iBV), Université Nice Sophia Antipolis, UMR 7277, 06100 Nice, France; CNRS, iBV, UMR 7277, 06100 Nice, France; INSERM, iBV, 06100 Nice, France; Laboratories of Excellence, Ion Channel Science and Therapeutics, Nice, France;
3
Institute of Biology Valrose (iBV), Université Nice Sophia Antipolis, UMR 7277, 06100 Nice, France; CNRS, iBV, UMR 7277, 06100 Nice, France; INSERM, iBV, 06100 Nice, France;
4
Department of Molecular and Cell Biology and Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720; Physical Bioscience Division, Lawrence Berkeley National Laboratory, Berkeley, CA.
5
Institute of Biology Valrose (iBV), Université Nice Sophia Antipolis, UMR 7277, 06100 Nice, France; CNRS, iBV, UMR 7277, 06100 Nice, France; INSERM, iBV, 06100 Nice, France; Laboratories of Excellence, Ion Channel Science and Therapeutics, Nice, France; sandoz@unice.fr.

Abstract

Twik-related K(+) channel 1 (TREK1), TREK2, and Twik-related arachidonic-acid stimulated K(+) channel (TRAAK) form the TREK subfamily of two-pore-domain K(+) (K2P) channels. Despite sharing up to 78% sequence homology and overlapping expression profiles in the nervous system, these channels show major differences in their regulation by physiological stimuli. For instance, TREK1 is inhibited by external acidification, whereas TREK2 is activated. Here, we investigated the ability of the members of the TREK subfamily to assemble to form functional heteromeric channels with novel properties. Using single-molecule pull-down (SiMPull) from HEK cell lysate and subunit counting in the plasma membrane of living cells, we show that TREK1, TREK2, and TRAAK readily coassemble. TREK1 and TREK2 can each heterodimerize with TRAAK, but do so less efficiently than with each other. We functionally characterized the heterodimers and found that all combinations form outwardly rectifying potassium-selective channels but with variable voltage sensitivity and pH regulation. TREK1-TREK2 heterodimers show low levels of activity at physiological external pH but, unlike their corresponding homodimers, are activated by both acidic and alkaline conditions. Modeling based on recent crystal structures, along with mutational analysis, suggests that each subunit within a TREK1-TREK2 channel is regulated independently via titratable His. Finally, TREK1/TRAAK heterodimers differ in function from TRAAK homodimers in two critical ways: they are activated by both intracellular acidification and alkalinization and are regulated by the enzyme phospholipase D2. Thus, heterodimerization provides a means for diversifying functionality through an expansion of the channel types within the K2P channels.

KEYWORDS:

combinatorial diversity; heteromerization; leak current; potassium channels; single-molecule fluorescence

PMID:
27035963
PMCID:
PMC4839437
DOI:
10.1073/pnas.1522459113
[Indexed for MEDLINE]
Free PMC Article

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