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Derepression masquerades as activation in a pentameric ligand-gated ion channel

Tessier, C. J. G.; Emlaw, J. R.; Sturgeon, R. M.; daCosta, C. J. B.

2022-09-15 biophysics
10.1101/2022.09.13.507804 bioRxiv
Show abstract

Agonists are ligands that bind to receptors and activate them. In the case of ligand-gated ion channels, such as the muscle-type nicotinic acetylcholine receptor, mechanisms of agonist activation have been studied for decades. Taking advantage of a reconstructed ancestral muscle-type {beta}-subunit that forms spontaneously activating homopentamers, here we show that incorporation of human muscle-type -subunits represses spontaneous activity, and furthermore that the presence of agonist relieves this -subunit-dependent repression. Our results demonstrate that rather than provoking channel activation/opening, agonists may instead inhibit the inhibition of intrinsic spontaneous activity. Thus, agonist activation may be the apparent manifestation of agonist-induced derepression. These results provide insight into intermediate states that precede channel opening and have implications for the interpretation of agonism in ligand-gated ion channels.

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