Structural determinants and regulation of spontaneous activity in GABAA receptors

Abstract

GABAA receptors are vital for controlling neuronal excitability and can display significant levels of constitutive activity that contributes to tonic inhibition. However, the mechanisms underlying spontaneity are poorly understood. Here we demonstrate a strict requirement for β3 subunit incorporation into receptors for spontaneous gating, facilitated by α4, α6 and δ subunits. The crucial molecular determinant involves four amino acids (GKER) in the β3 subunit’s extracellular domain, which interacts with adjacent receptor subunits to promote transition to activated, open channel conformations. Spontaneous activity is further regulated by β3 subunit phosphorylation and by allosteric modulators including neurosteroids and benzodiazepines. Promoting spontaneous activity reduced neuronal excitability, indicating that spontaneous currents will alter neural network activity. This study demonstrates how regional diversity in GABAA receptor isoform, protein kinase activity, and neurosteroid levels, can impact on tonic inhibition through the modulation of spontaneous GABAA receptor gating.

Transcriptome comparative analysis of ovarian follicles reveals the key genes and signaling pathways implicated in hen egg production

“…Previous studies have reported that GABRA1 gene encodes γ-aminobutyric acid type A receptor α1 subunit (GABRA1) is one subtype of the neurotransmitter γ-aminobutyric acid (GABA) activating GABA A receptors that act as the components of the gamma-aminobutyric acid signaling pathway [ 54 , 55 ]. The heteropentameric receptors are formed from an array of subunits (α1–6, β1–3, γ1–3, δ, ε, π, θ and ρ1–3), producing receptors with diverse functional and pharmacological properties [ 56 – 58 ]. The GABA A receptors are vital for controlling neuronal excitability and can display significant levels of constitutive activity that contributes to tonic inhibition [ 58 ].…”

“…The heteropentameric receptors are formed from an array of subunits (α1–6, β1–3, γ1–3, δ, ε, π, θ and ρ1–3), producing receptors with diverse functional and pharmacological properties [ 56 – 58 ]. The GABA A receptors are vital for controlling neuronal excitability and can display significant levels of constitutive activity that contributes to tonic inhibition [ 58 ]. It has been established that the progesterone metabolite allopregnanolone, a potent modulator of the GABA A receptor, is sedative in high concentrations but may precipitate paradoxical adverse effects on mood at levels corresponding to luteal phase concentrations in susceptible women [ 59 ].…”

Ancestral acetylcholine receptor β-subunit forms homopentamers that prime before opening spontaneously

“…In each case, if the residue implicated is conserved across all three subunits the highlight is faded. Corresponding references for each position are indicated ( a–n ), where a: Torres and Weiss, 2002 ; b: Beckstead, 2002 ; c: Miller et al, 2008 ; d: Nayak et al, 2012 ; e: Purohit and Auerbach, 2009 ; f: Taylor et al, 1999 ; g: Sexton et al, 2021 ; h: Alves et al, 2011 ; i: Hannan and Smart, 2018 ; j: Pan et al, 1997 ; k: Mukhtasimova et al, 2009 ; l: Ohno et al, 1995 ; m: Grosman and Auerbach, 2000 ; n: Engel et al, 1996 .

Appendix 1—figure 2.

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“…Provided is the multiple sequence alignment ( Supplementary file 1 ) used to identify residues that differ between β Anc , β AncS , and the human β-subunit, and that also align with residues shown to be important for homomeric pLGIC assembly ( Alves et al, 2011 ; Hannan and Smart, 2018 ; Sexton et al, 2021 ; Taylor et al, 1999 ) and spontaneous activity ( Beckstead, 2002 ; Engel et al, 1996 ; Grosman and Auerbach, 2000 ; Miller et al, 2008 ; Mukhtasimova et al, 2009 ; Nayak et al, 2012 ; Ohno et al, 1995 ; Pan et al, 1997 ; Purohit and Auerbach, 2009 ; Torres and Weiss, 2002 ; Appendix 1—figure 1 ). Also shown is a local alignment of the second transmembrane region (M2) of the adult human muscle-type subunits (α-, β-, δ-, and ε-subunits), as well as β Anc and β AncS ( Appendix 1—figure 2 ) highlighting differences in well-characterized determinants of single-channel conductance ( Imoto et al, 1991 ; Imoto et al, 1988 ) and open-channel block ( Charnet et al, 1990 ; Leonard et al, 1988 ; Pascual and Karlin, 1998 ).…”

Preventing Phosphorylation of the GABAAR β3 Subunit Compromises the Behavioral Effects of Neuroactive Steroids

“…In both cultured neurons and hippocampal brain slices these events correlate with sustained increases in the efficacy of tonic inhibition ( Abramian et al, 2010 , 2014 ; Adams et al, 2015 ; Modgil et al, 2017 ). Phosphorylation of the β3 subunit can induce spontaneous channel openings of α4β3δ receptors which have an impact upon agonist/antagonist pharmacology and neuronal excitability ( Wlodarczyk et al, 2013 ; O’Neill and Sylantyev, 2018 ; Dalby et al, 2020 ; Sexton et al, 2021 ).…”