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The pre‐M1 segment of the α1 subunit is a transduction element in the activation of the GABA A receptor
Author(s) -
Keramidas Angelo,
Kash Thomas L.,
Harrison Neil L.
Publication year - 2006
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2005.102756
Subject(s) - transmembrane domain , biophysics , agonist , protein subunit , transmembrane protein , chemistry , mutant , gabaa receptor , partial agonist , receptor , allosteric regulation , biochemistry , biology , gene
The binding of the neurotransmitter GABA induces conformational changes in the GABA A receptor (GABA A R), leading to the opening of a gate that controls ion permeation through an integral transmembrane pore. A number of structural elements within each subunit, located near the membrane interface, are believed to undergo relative movements during this activation process. In this study, we explored the functional role of the β‐10 strand (pre‐M1 segment), which connects the extracellular domain to the transmembrane domain. In α 1 β 2 γ 2s GABA A Rs, analysis of the 12 residues of the β‐10 strand in the α 1 subunit proximal to the first transmembrane domain identified two residues, α 1 V212 and α 1 K220, in which mutations produced rightward shifts in the GABA concentration–response relationship and also reduced the relative efficacy of the partial agonist, piperidine‐4‐sulphonic acid. Ultra‐fast agonist techniques were applied to mutant α 1 (K220A)β 2 γ 2s GABA A Rs and revealed that the macroscopic functional deficit in this mutant could be attributed to a slowing of the opening rate constant, from ∼1500 s −1 in wild‐type (WT) channels to ∼730 s −1 in the mutant channels, and a reduction in the time spent in the active state for the mutant. These changes were accompanied by a decrease in agonist affinity, with half‐maximal activation rates achieved at 0.77 m m GABA in WT and 1.4 m m GABA in the α 1 (K220A)β 2 γ 2s channels. The β‐10 strand (pre‐M1 segment) emerges, from this and other studies, as a key functional component in the activation of the GABA A R.