Evidence for distinct conformations of the two α1 subunits in diazepam-bound GABAA receptors

Daniel B. Williams, Myles H. Akabas

Research output: Contribution to journalArticle

18 Scopus citations

Abstract

Benzodiazepines allosterically modulate GABAA receptors to increase currents induced by submaximal GABA concentrations. Benzodiazepine-induced conformational changes in the transmembrane domain increase the reactivity of cysteines substituted for a subset of residues in the α1 subunit M3 membrane-spanning segment. With the cysteine-substitution mutant α1F296Cβ1γ2 we previously noted that p-chloromercuribenzenesulfonate (pCMBS-) modification in the presence of diazepam potentiated subsequent GABA-induced currents. In contrast, pCMBS- modification in the presence of GABA caused inhibition of subsequent responses. We now show that in the presence of diazepam, pCMBS- only reacts with the engineered cysteine in one of the two α subunits; whereas, in the presence of GABA, pCMBS- reacts with the cysteine in the other α subunit, or with both cysteines. This implies that the two α subunits have distinct conformations in the diazepam-bound state. Based on analysis of single channel kinetic data, others have hypothesized that diazepam only alters the GABA affinity of one of the two GABA binding sites. The results presented here provide structural evidence to support the hypothesis that diazepam binding only alters the conformation of one of the two α subunits in a GABAA receptor and provides new insights into the mechanism of allosteric potentiation by benzodiazepines.

Original languageEnglish (US)
Pages (from-to)539-545
Number of pages7
JournalNeuropharmacology
Volume41
Issue number5
DOIs
StatePublished - Oct 14 2001

Keywords

  • Acetylcholine
  • Anesthesia
  • Benzodiazepine
  • Cysteine
  • Ethanol
  • Ion channel

ASJC Scopus subject areas

  • Pharmacology
  • Cellular and Molecular Neuroscience

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