PT  - JOURNAL ARTICLE
AU  - Williams, Daniel B.
AU  - Akabas, Myles H.
TI  - Benzodiazepines Induce a Conformational Change in the Region of the γ-Aminobutyric Acid Type A Receptor  α<sub>1</sub>-Subunit M3 Membrane-Spanning Segment
AID  - 10.1124/mol.58.5.1129
DP  - 2000 Nov 01
TA  - Molecular Pharmacology
PG  - 1129--1136
VI  - 58
IP  - 5
4099  - http://molpharm.aspetjournals.org/content/58/5/1129.short
4100  - http://molpharm.aspetjournals.org/content/58/5/1129.full
SO  - Mol Pharmacol2000 Nov 01; 58
AB  - Benzodiazepine binding to γ-aminobutyric acid type A (GABAA) receptors allosterically modulates GABA binding and increases the currents induced by submaximal GABA concentrations. Benzodiazepines induce conformational changes in the GABA-binding site in the extracellular domain, but it is uncertain whether these conformational changes extend into the membrane-spanning domain where the channel gate is located. Alone, benzodiazepines do not open the channel. We used the substituted-cysteine-accessibility method to investigate diazepam-induced conformational changes in the region of the α1-subunit M3 membrane-spanning segment. In the absence of diazepam or GABA, pCMBS− did not react at a measurable rate with cysteine-substitution mutants between α1Phe296 and α1Glu303. In the presence of 100 nM diazepam, pCMBS− reacted with α1F296C, α1F298C, and α1L301C but not with the other cysteine mutants between α1Phe296 and α1Glu303. These three mutants are a subset of the five residues that we previously showed reacted with pCMBS− applied in the presence of GABA. The pCMBS− reaction rates with these three cysteine mutants were similar in the presence of diazepam and GABA. Thus, diazepam, which binds to the extracellular domain, induces a conformational change in the membrane-spanning domain that is similar to a portion of the change induced by GABA. Because diazepam does not open the channel, these results provide structural evidence that the diazepam-bound state represents an intermediate conformation distinct from the open and resting/closed states of the receptor. The diazepam-induced conformational change in the M3 segment vicinity may be related to the mechanism of allosteric potentiation.