Functional asymmetry of the conserved cystine loops in αβγ GABAA receptors revealed by the response to GABA activation and drug potentiation

Tierney, M. Louise, Luu, Tien and Gage, Peter W. (2008) Functional asymmetry of the conserved cystine loops in αβγ GABAA receptors revealed by the response to GABA activation and drug potentiation. The International Journal of Biochemistry & Cell Biology, 40 5: 968-979. doi:10.1016/j.biocel.2007.10.029


Author Tierney, M. Louise
Luu, Tien
Gage, Peter W.
Title Functional asymmetry of the conserved cystine loops in αβγ GABAA receptors revealed by the response to GABA activation and drug potentiation
Journal name The International Journal of Biochemistry & Cell Biology   Check publisher's open access policy
ISSN 1357-2725
Publication date 2008
Year available 2008
Sub-type Article (original research)
DOI 10.1016/j.biocel.2007.10.029
Volume 40
Issue 5
Start page 968
End page 979
Total pages 12
Place of publication Exeter, England
Publisher Elsevier/Pergamon
Language eng
Subject 11 Medical and Health Sciences
1109 Neurosciences
Abstract Ligand-gated ion channels respond to specific neurotransmitters by transiently opening an integral membrane ion-selective pore, allowing ions to move down their electrochemical gradient. A distinguishing feature of all members of the ligand-gated ion channel superfamily is the presence of a 13-amino acid disulfide loop (Cys-loop) in the extracellular ligand-binding domain. Structural data derived from the acetylcholine receptor place this loop at the interface between the ligand-binding domain and the transmembrane pore-forming domain where it is ideally located to participate in coupling ligand binding to channel opening. We have introduced specific mutations into a conserved motif at the mid-point of the Cys-loop of the GABAA receptor subunits α1, β2 and γ2S where the sequence reads aromatic, proline, aliphatic (ArProAl motif). Receptors carrying a mutation in the Cys-loop of one of their subunits were expressed in L929 cells and responses to both GABA and drugs were assessed using the whole-cell patch clamp technique. Drug potentiation and direct activation were significantly enhanced by mutations in this Cys-loop but these effects were subunit-dependent. Currents in response to agonists were larger when mutations were carried in the α and β subunits but not in the γ subunit. In contrast, potentiation of current responses by diazepam, etomidate and pentobarbital were all enhanced when mutations were carried in the α and γ subunits, but not the β subunit. Since the disruption of interactions mediated through the ArProAl motif enhances the mutant receptor's response to both agonist and drugs we suggest that this motif in the Cys-loop of the wild-type receptor participates in interactions that create activation barriers to conformational changes during channel gating.
Keyword GABAA receptor
Cys-loop
Gating
Electrophysiology
Diazepam
Q-Index Code C1
Q-Index Status Provisional Code

Document type: Journal Article
Sub-type: Article (original research)
Collections: Excellence in Research Australia (ERA) - Collection
Queensland Brain Institute Publications
 
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Created: Wed, 23 Dec 2009, 11:14:37 EST by Macushla Boyle on behalf of Queensland Brain Institute