Biology subjects

Nors, J. W.

Publications and source records attributed to Nors, J. W..

2 recordsLinked to original sources

bioRxiv2023

Asymmetric roles for M2-M3 linkers of specific GABAA receptor subunits in the intrinsic closed-open equilibrium and its modulation by the benzodiazepine diazepam

GABAA receptors (GABAARs) are neurotransmitter-gated ion channels critical for inhibitory synaptic transmission as well as the molecular target for benzodiazepines (BZDs), one of the most widely prescribed class of psychotropic drugs today. Despite structural insight into the conformations underlying functional channel states, the detailed molecular interactions involved in conformational transitions and the physical basis for their modulation by BZDs are not fully understood. We previously identified that alanine substitution at the central residue in the 1 subunit M2-M3 linker (V279A) enhances the efficiency of linkage between the BZD site and the pore gate. Here, we expand on this work by investigating the effect of alanine substitutions at the analogous positions in the M2-M3 linkers of {beta}2 (I275A) and {gamma}2 (V290A) subunits, which together with 1 comprise typical heteromeric 1{beta}2{gamma}2 synaptic GABAARs. We find that these mutations confer subunit-specific effects on the intrinsic pore closed-open equilibrium and its modulation by the BZD diazepam (DZ). The mutations 1(V279A) or {gamma}2(V290A) bias the channel toward a closed conformation, whereas {beta}2(I275A) biases the channel toward an open conformation to the extent that the channel becomes leaky and opens spontaneously in the absence of agonist (e.g., GABA). In contrast, only 1(V279A) enhances the efficiency of DZ-to-pore linkage, whereas mutations in the other two subunits have no effect. These observations show that the central residue in the M2-M3 linkers of distinct subunits in synaptic 1{beta}2{gamma}2 GABAARs contribute asymmetrically to the intrinsic closed-open equilibrium and its modulation by DZ.

biophysics↗

bioRxiv2020

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

Benzodiazepines (BZDs) are a class of widely prescribed psychotropic drugs. Their anxiolytic and sedative effects are conferred by modulating the activity of GABAA receptors (GABAARs), which are the primary inhibitory neurotransmitter receptors throughout the central nervous system. However, the physical mechanism by which BZDs exert their effects on the receptor is poorly understood. In particular, BZDs require coapplication with an agonist to effectively open the channel pore, making it difficult to dissect whether the drug has altered either agonist binding or channel gating as these two processes are intimately coupled. To isolate effects on gating we used a spontaneously active gain of function mutant (1L9T{beta}2{gamma}2L) that is directly gated by BZDs alone in the absence of agonist. In the 1L9T background we explored effects of alanine substitutions throughout the 1M2-M3 linker on modulation of the channel pore by the BZD positive modulator diazepam (DZ). The M2-M3 linker is known to be an important element for channel activation. Linker mutations generally impaired unliganded pore opening, indicating that side chain interactions are important for channel gating in the absence of bound agonist. All but one mutation had no effect on the transduction of chemical energy from DZ binding to pore gating. Strikingly, 1V279A doubles DZs energetic contribution to gating, whereas larger side chains at this site do not. In a wild-type background 1V279A enhances DZ-potentiation of currents evoked by saturating GABA, consistent with a direct effect on the pore closed/open equilibrium. Our observations identify an important residue regulating coupling between the BZD site and the pore gate, thereby shedding new light on the molecular mechanism of a frequently prescribed class of psychotropic drugs.

molecular biology↗