The role of loops B and C in determining the potentiation of GABAA receptors by midazolam

• Type of Material: Article
• Authors: Olivia A. Moody, Emory University; Andrew Jenkins, Emory University
• Language: English
• Date: 2018-12-01
• Publisher: Wiley Open Access: Various Creative Commons Licenses
• Publication Version: Final Published Version
• Copyright Statement: © 2018 The Authors. Pharmacology Research & Perspectives published by John Wiley & Sons Ltd, British Pharmacological Society and American Society for Pharmacology and Experimental Therapeutics.
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1002/prp2.433
• Title of Journal or Parent Work: Pharmacology Research and Perspectives
• ISSN: 2052-1707
• Volume: 6
• Issue: 6
• Start Page: e00433
• End Page: e00433
• Grant/Funding Information: This work was supported by the National Institutes of Health [GM008602 (O.A.M), NS007480 (O.A.M.), and NS089719 (A.J.); National Institute of General Medical Sciences
• Keywords: benzodiazepine; canonical loops; allosteric modulator; GABA(A) receptor
• Research Categories: Health Sciences, Pharmacology

Abstract

Many benzodiazepines are positive allosteric modulators (PAMs) of GABAA receptors that cause sedation, hypnosis, and anxiolysis. Benzodiazepines bind GABAA receptors at the extracellular interface of the α and γ subunits. Within the α subunit, the benzodiazepine binding site is defined by three highly conserved structural loops, loops A-C. Although previous mutagenesis studies have identified His102 in Loop A as important for benzodiazepine modulation of GABAA receptors, the functional roles of many of the other conserved residues in loops A-C remain incompletely understood. In this study, we made single mutations in loops A-C of the benzodiazepine binding-site across all six α subunits. We used whole-cell patch clamp recording to measure the functional effects of these mutations on midazolam potentiation. The results showed that mutating the threonine in loop B and serine in loop C (Thr163 and S206 in human α1) did not abolish the receptors' responsiveness to midazolam, as the α1(H102R) mutation did. The loop C mutations exhibited a novel array of α-isoform specific effects on midazolam potentiation. The α3(S230I) and α5(S209I) mutations had the largest effect on midazolam potentiation, increasing the efficacy of midazolam. Novel benzodiazepines targeting loop C may represent a future direction for designing new drugs that specifically alter the activity of α3- and α5-containing GABAA receptors.