Identifying Barbiturate Binding Sites in a Nicotinic Acetylcholine Receptor with [<sup>3</sup>H]Allyl <i>m</i>-Trifluoromethyldiazirine Mephobarbital, a Photoreactive Barbiturate

Hamouda, Ayman K.; Stewart, Deirdre S.; Chiara, David C.; Savechenkov, Pavel Y.; Bruzik, Karol S.; Cohen, Jonathan B.

doi:10.1124/mol.113.090985

Cited by 23 publications

(26 citation statements)

References 42 publications

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“…In this regard, meprobamate is comparable to carisoprodol (Gonzalez et al, 2009b). Recent photoaffinity labeling studies have provided considerable evidence that barbiturates bind to inter-subunit interfaces in GABA A (Chiara et al, 2013) and nicotinic (Hamouda et al, 2014) receptors. With regard to GABA A receptors, a photoreactive barbiturate binds to a number of residues at both the α–β and γ–β interfaces in the transmembrane domain (Chiara et al, 2013).…”

Section: Discussionmentioning

confidence: 99%

Assessment of direct gating and allosteric modulatory effects of meprobamate in recombinant GABAA receptors

Kumar

Dillon

2016

European Journal of Pharmacology

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Meprobamate is a schedule II anxiolytic and the primary metabolite of the muscle relaxant carisoprodol. Meprobamate modulates GABAA (γ-aminobutyric acid type A) receptors, and has barbiturate-like activity. To gain insight into its actions, we have conducted a series of studies using recombinant GABAA receptors. In αxβzγ GABAA receptors (where x = 1–6 and z = 1–3), the ability to enhance GABA-mediated current was evident for all α subunit isoforms, with the largest effect observed in α5-expressing receptors. Direct gating was present with all α subunits, although attenuated in α3-expressing receptors. Allosteric and direct effects were comparable in α1β1γ2 and α1β2γ2 receptors, whereas allosteric effects were enhanced in α1β2 compared to α1β2γ2 receptors. In “extrasynaptic” (α1β3δ and α4β3δ) receptors, meprobamate enhanced EC20 and saturating GABA currents, and directly activated these receptors. The barbiturate antagonist bemegride attenuated direct effects of meprobamate. Whereas pentobarbital directly gated homomeric β3 receptors, meprobamate did not, and instead blocked the spontaneously open current present in these receptors. In wild type homomeric ρ1 receptors, pentobarbital and meprobamate were ineffective in direct gating; a mutation known to confer sensitivity to pentobarbital did not confer sensitivity to meprobamate. Our results provide insight into the actions of meprobamate and parent therapeutic agents such as carisoprodol. Whereas in general actions of meprobamate were comparable to those of carisoprodol, differential effects of meprobamate at some receptor subtypes suggest potential advantages of meprobamate may be exploited. A re-assessment of previously synthesized meprobamate-related carbamate molecules for myorelaxant and other therapeutic indications is warranted.

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Section: Discussionmentioning

confidence: 99%

Assessment of direct gating and allosteric modulatory effects of meprobamate in recombinant GABAA receptors

Kumar

Dillon

2016

European Journal of Pharmacology

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“…A variety of anesthetic photo-affinity reagents, including 3-azi- octanol, m-azi-propofol, azi-etomidate, pTFD-etomidate, TDBzl-etomidate, and mTFD-MPAB label residues in the Torpedo nAChR ion channel (Hamouda et al, 2014; Hamouda et al, 2011; Jayakar et al, 2013; Nirthanan et al, 2008; Pratt et al, 2000; Ziebell et al, 2004) (Figure 2). Halothane is the exception, probably because this drug selectively photolabels tyrosines (Chiara et al, 2003).…”

Section: Interfacial General Anesthetic Sites In Nicotinic Ach Recmentioning

confidence: 99%

“…A structural model of Torpedo nAChR (Hamouda et al, 2014) showing peptide backbone as ribbons. Molecular graphics and analyses were performed with the UCSF Chimera package (Pettersen et al, 2004).…”

Section: Figurementioning

confidence: 99%

Anesthetics target interfacial transmembrane sites in nicotinic acetylcholine receptors

2015

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General anesthetics are a heterogeneous group of small amphiphilic ligands that interact weakly at multiple allosteric sites on many pentameric ligand gated ion channels (pLGICs), resulting in either inhibition, potentiation of channel activity, or both. Allosteric principles imply that modulator sites must change configuration and ligand affinity during receptor state transitions. Thus, general anesthetics and related compounds are useful both as state-dependent probes of receptor structure and as potentially selective modulators of pLGIC functions. This review focuses on general anesthetic sites in nicotinic acetylcholine receptors, which were among the first anesthetic-sensitive pLGIC experimental models studied, with particular focus on sites formed by transmembrane domain elements. Structural models place many of these sites at interfaces between two or more pLGIC transmembrane helices both within subunits and between adjacent subunits, and between transmembrane helices and either lipids (the lipid-protein interface) or water (i.e. the ion channel). A single general anesthetic may bind at multiple allosteric sites in pLGICs, producing a net effect of either inhibition (e.g. blocking the ion channel) or enhanced channel gating (e.g. inter-subunit sites). Other general anesthetic sites identified by photolabeling or crystallography are tentatively linked to functional effects, including intra-subunit helix bundle sites and the lipid-protein interface.

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“…Intersubunitbinding sites in the TMD for positive and negative allosteric modulators have been identified in nicotinic acetylcholine receptors and serotonin 5-HT 3 receptors containing cationselective channels (49,50). Also, general anesthetics of diverse chemical structure that act as GABA A R-positive allosteric modulators bind with varying selectivities to each of the intersubunit sites in the GABA A R TMD.…”

Section: S-[mentioning

confidence: 99%

Positive and Negative Allosteric Modulation of an α1β3γ2 γ-Aminobutyric Acid Type A (GABAA) Receptor by Binding to a Site in the Transmembrane Domain at the γ+-β− Interface

Jayakar

Zhou

Savechenkov

et al. 2015

Journal of Biological Chemistry

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Background: For some chiral barbiturates, one isomer potentiates and the other inhibits GABA responses by binding to unknown sites. Results: A photoreactive convulsant barbiturate identifies a transmembrane intersubunit-binding site between the ␥ and ␤ subunits. Conclusion: Positive and negative allosteric modulators can bind to a common intersubunit site. Significance: This study defines a novel mode of regulation of GABA A R responses.

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Identifying Barbiturate Binding Sites in a Nicotinic Acetylcholine Receptor with [³H]Allyl m-Trifluoromethyldiazirine Mephobarbital, a Photoreactive Barbiturate

Cited by 23 publications

References 42 publications

Assessment of direct gating and allosteric modulatory effects of meprobamate in recombinant GABAA receptors

Assessment of direct gating and allosteric modulatory effects of meprobamate in recombinant GABAA receptors

Anesthetics target interfacial transmembrane sites in nicotinic acetylcholine receptors

Positive and Negative Allosteric Modulation of an α1β3γ2 γ-Aminobutyric Acid Type A (GABAA) Receptor by Binding to a Site in the Transmembrane Domain at the γ+-β− Interface

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Identifying Barbiturate Binding Sites in a Nicotinic Acetylcholine Receptor with [3H]Allyl m-Trifluoromethyldiazirine Mephobarbital, a Photoreactive Barbiturate

Cited by 23 publications

References 42 publications

Assessment of direct gating and allosteric modulatory effects of meprobamate in recombinant GABAA receptors

Assessment of direct gating and allosteric modulatory effects of meprobamate in recombinant GABAA receptors

Anesthetics target interfacial transmembrane sites in nicotinic acetylcholine receptors

Positive and Negative Allosteric Modulation of an α1β3γ2 γ-Aminobutyric Acid Type A (GABAA) Receptor by Binding to a Site in the Transmembrane Domain at the γ+-β− Interface

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Identifying Barbiturate Binding Sites in a Nicotinic Acetylcholine Receptor with [³H]Allyl m-Trifluoromethyldiazirine Mephobarbital, a Photoreactive Barbiturate