A critical residue in the α1M2-M3 linker regulating mammalian GABAA receptor pore gating by diazepam.

Joseph W Nors,Marcel P Goldschen-Ohm,Shipra Gupta

doi:10.7554/elife.64400

Abstract

Benzodiazepines (BZDs) are a class of widely prescribed psychotropic drugs that modulate activity of GABAA receptors (GABAARs), neurotransmitter-gated ion channels critical for synaptic transmission. However, the physical basis of this modulation is poorly understood. We explore the role of an important gating domain, the α1M2-M3 linker, in linkage between the BZD site and pore gate. To probe energetics of this coupling without complication from bound agonist, we use a gain of function mutant (α1L9'Tβ2γ2L) directly activated by BZDs. We identify a specific residue whose mutation (α1V279A) more than doubles the energetic contribution of the BZD positive modulator diazepam (DZ) to pore opening and also enhances DZ potentiation of GABA-evoked currents in a wild-type background. In contrast, other linker mutations have little effect on DZ efficiency, but generally impair unliganded pore opening. Our observations reveal an important residue regulating BZD-pore linkage, thereby shedding new light on the molecular mechanism of these drugs.

Highlights

Benzodiazepines (BZDs) (e.g. Valium, Xanax) are one of the most widely prescribed psychotropic drugs today
Each pentameric GABAA receptors (GABAARs) is comprised of subtype-specific combinations of five homologous but nonidentical subunits (a1-6, b1-3, g1-3, d, e, p, q, r1-3) that together form a central chloride conducting pore (Figure 1; Olsen and Sieghart, 2008)
GABAARs provide a critical balance with excitatory signaling for normal neural function, and not surprisingly, their dysfunction is related to disorders such as epilepsy, autism spectrum disorder, intellectual disability, schizophrenia, and neurodevelopmental disorders such as fragile X syndrome

Summary

Introduction

Benzodiazepines (BZDs) (e.g. Valium, Xanax) are one of the most widely prescribed psychotropic drugs today. An estimated nearly 100 million adults in the United States are prescribed a BZD annually (Agarwal and Landon, 2019; Bachhuber et al, 2016; Olfson et al, 2015). Their anxiolytic and sedative properties are used as therapies for conditions including anxiety, panic, insomnia, seizures, muscle spasms, pain, and alcohol withdrawal (Mohler et al, 2002). Each pentameric GABAAR is comprised of subtype-specific combinations of five homologous but nonidentical subunits (a1-6, b1-3, g1-3, d, e, p, q, r1-3) that together form a central chloride conducting pore (Figure 1; Olsen and Sieghart, 2008).

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