title: Mechanism of alpha-subunit selectivity of benzodiazepine pharmacology at gamma-aminobutyric acid type A receptors.
abstract: Benzodiazepine pharmacology at the GABA(A) receptor is dependent on the alpha and gamma subunit isoforms present. Ligands with higher affinity for certain isoforms--selective compounds--have been classified into benzodiazepine type I and II and into diazepam-sensitive and diazepam-insensitive receptors. A single amino acid position (alpha1G201/alpha3E225) has been identified which discriminates BZI and BZII receptors. The role of this residue has been explored by mutagenesis of alpha1 position 201 and the pharmacology of recombinant receptors examined using BZI receptor agonists. Ligand affinity is reduced by increasing side chain volume at alpha1G201 suggesting that steric inhibition underlies alpha-subunit selectivity. A second amino acid (alpha1H102/alpha6R100) determines diazepam sensitivity. The nature of the amino acid at this position was also examined by mutagenesis. Flumazenil and Ro15-4513 (ethyl 8-azido-6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5-a]-[1,4]benzodiazepine-3-carboxylate) binding affinity correlated weakly with the amino acid hydrophobicity suggesting a weak hydrophobic interaction between the ligand and alpha1H102.
authors.affiliation: Merck Sharp and Dohme Research Laboratories, Neuroscience Research Centre, Terlings Park, Eastwick Road, Essex CM20 2QR, Harlow, UK. Peter_Wingrove@Merck.com
authors.forename: Peter B
authors.initials: PB
authors.lastname: Wingrove
authors.forename: Patrick
authors.initials: P
authors.lastname: Safo
authors.forename: Lola
authors.initials: L
authors.lastname: Wheat
authors.forename: Sally A
authors.initials: SA
authors.lastname: Thompson
authors.forename: Keith A
authors.initials: KA
authors.lastname: Wafford
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Whiting
mesh_terms: D000818:Animals; D014151:Anti-Anxiety Agents / Q000145:classification / Q000378:metabolism* / Q000494:pharmacology; D001667:Binding, Competitive / Q000187:drug effects; D002460:Cell Line; D003975:Diazepam / Q000378:metabolism / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D005442:Flumazenil / Q000378:metabolism; D005445:Flunitrazepam / Q000494:pharmacology; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D009154:Mutation; D009865:Oocytes / Q000187:drug effects / Q000502:physiology; D021122:Protein Subunits; D011724:Pyridazines / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D011869:Radioligand Assay; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism*; D014316:Tritium; D014982:Xenopus laevis; D000077334:Zolpidem; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D014151:Anti-Anxiety Agents; D021122:Protein Subunits; D011724:Pyridazines; D011725:Pyridines; D011963:Receptors, GABA-A; D014316:Tritium; D005442:Flumazenil; D005680:gamma-Aminobutyric Acid; D005445:Flunitrazepam; C021604:CL 218872; D000077334:Zolpidem; D003975:Diazepam