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Mol Pharmacol
2008 Dec 01;746:1687-95. doi: 10.1124/mol.108.050500.
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Tryptophan mutations at azi-etomidate photo-incorporation sites on alpha1 or beta2 subunits enhance GABAA receptor gating and reduce etomidate modulation.
Stewart D
,
Desai R
,
Cheng Q
,
Liu A
,
Forman SA
.
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The potent general anesthetic etomidate produces its effects by enhancing GABA(A) receptor activation. Its photolabel analog [(3)H]azi-etomidate labels residues within transmembrane domains on alpha and beta subunits: alphaMet236 and betaMet286. We hypothesized that these methionines contribute to etomidate sites formed at alpha-beta subunit interfaces and that increasing side-chain bulk and hydrophobicity at either locus would mimic etomidate binding and block etomidate effects. Channel activity was electrophysiologically quantified in alpha(1)beta(2)gamma(2L) receptors with alpha(1)M236W or beta(2)M286W mutations, in both the absence and the presence of etomidate. Measurements included spontaneous activation, GABA EC(50), etomidate agonist potentiation, etomidate direct activation, and rapid macrocurrent kinetics. Both alpha(1)M236W and beta(2)M286W mutations induced spontaneous channel opening, lowered GABA EC(50), increased maximal GABA efficacy, and slowed current deactivation, mimicking effects of etomidate on alpha(1)beta(2)gamma(2L) channels. These changes were larger with alpha(1)M236W than with beta(2)M286W. Etomidate (3.2 muM) reduced GABA EC(50) much less in alpha(1)M236Wbeta(2)gamma(2L) receptors (2-fold) than in wild type (23-fold). However, etomidate was more potent and efficacious in directly activating alpha(1)M236Wbeta(2)gamma(2L) compared with wild type. In alpha(1)beta(2)M286Wgamma(2L) receptors, etomidate induced neither agonist-potentiation nor direct channel activation. These results support the hypothesis that alpha(1)Met236 and beta(2)Met286 are within etomidate sites that allosterically link to channel gating. Although alpha(1)M236W produced the larger impact on channel gating, beta(2)M286W produced more profound changes in etomidate sensitivity, suggesting a dominant role in drug binding. Furthermore, quantitative mechanistic analysis demonstrated that wild-type and mutant results are consistent with the presence of only one class of etomidate sites mediating both agonist potentiation and direct activation.
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Akk,
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Bali,
Defining the propofol binding site location on the GABAA receptor.
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,
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Baumann,
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2002,
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,
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Bianchi,
Neurosteroids shift partial agonist activation of GABA(A) receptor channels from low- to high-efficacy gating patterns.
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Boileau,
The relative amount of cRNA coding for gamma2 subunits affects stimulation by benzodiazepines in GABA(A) receptors expressed in Xenopus oocytes.
2002,
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,
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Boileau,
Effects of gamma2S subunit incorporation on GABAA receptor macroscopic kinetics.
2003,
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,
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Chang,
A single M1 residue in the beta2 subunit alters channel gating of GABAA receptor in anesthetic modulation and direct activation.
2003,
Pubmed
,
Xenbase
Chang,
Stoichiometry of a recombinant GABAA receptor.
1996,
Pubmed
,
Xenbase
Chang,
Allosteric activation mechanism of the alpha 1 beta 2 gamma 2 gamma-aminobutyric acid type A receptor revealed by mutation of the conserved M2 leucine.
1999,
Pubmed
,
Xenbase
Findlay,
Allosteric modulation in spontaneously active mutant gamma-aminobutyric acidA receptors.
2001,
Pubmed
,
Xenbase
Greenfield,
Mutation of the GABAA receptor M1 transmembrane proline increases GABA affinity and reduces barbiturate enhancement.
2002,
Pubmed
,
Xenbase
Hill-Venning,
Subunit-dependent interaction of the general anaesthetic etomidate with the gamma-aminobutyric acid type A receptor.
1997,
Pubmed
,
Xenbase
Hosie,
Endogenous neurosteroids regulate GABAA receptors through two discrete transmembrane sites.
2006,
Pubmed
Husain,
2-(3-Methyl-3H-diaziren-3-yl)ethyl 1-(1-phenylethyl)-1H-imidazole-5-carboxylate: a derivative of the stereoselective general anesthetic etomidate for photolabeling ligand-gated ion channels.
2003,
Pubmed
,
Xenbase
Jenkins,
Evidence for a common binding cavity for three general anesthetics within the GABAA receptor.
2001,
Pubmed
Jurd,
General anesthetic actions in vivo strongly attenuated by a point mutation in the GABA(A) receptor beta3 subunit.
2003,
Pubmed
Krasowski,
Methionine 286 in transmembrane domain 3 of the GABAA receptor beta subunit controls a binding cavity for propofol and other alkylphenol general anesthetics.
2001,
Pubmed
Krasowski,
4D-QSAR analysis of a set of propofol analogues: mapping binding sites for an anesthetic phenol on the GABA(A) receptor.
2002,
Pubmed
,
Xenbase
Krasowski,
Propofol and other intravenous anesthetics have sites of action on the gamma-aminobutyric acid type A receptor distinct from that for isoflurane.
1998,
Pubmed
Li,
Identification of a GABAA receptor anesthetic binding site at subunit interfaces by photolabeling with an etomidate analog.
2006,
Pubmed
Liao,
R (+) etomidate and the photoactivable R (+) azietomidate have comparable anesthetic activity in wild-type mice and comparably decreased activity in mice with a N265M point mutation in the gamma-aminobutyric acid receptor beta3 subunit.
2005,
Pubmed
Majewska,
Steroid hormone metabolites are barbiturate-like modulators of the GABA receptor.
1986,
Pubmed
Mercado,
Charged residues in the alpha1 and beta2 pre-M1 regions involved in GABAA receptor activation.
2006,
Pubmed
,
Xenbase
Reynolds,
Sedation and anesthesia mediated by distinct GABA(A) receptor isoforms.
2003,
Pubmed
Rüsch,
Gating allosterism at a single class of etomidate sites on alpha1beta2gamma2L GABA A receptors accounts for both direct activation and agonist modulation.
2004,
Pubmed
,
Xenbase
Rüsch,
Classic benzodiazepines modulate the open-close equilibrium in alpha1beta2gamma2L gamma-aminobutyric acid type A receptors.
2005,
Pubmed
,
Xenbase
Scheller,
Coupled and uncoupled gating and desensitization effects by pore domain mutations in GABA(A) receptors.
2002,
Pubmed
Serafini,
Structural domains of the human GABAA receptor 3 subunit involved in the actions of pentobarbital.
2000,
Pubmed
Sieghart,
Structure, pharmacology, and function of GABAA receptor subtypes.
2006,
Pubmed
Siegwart,
Molecular determinants for the action of general anesthetics at recombinant alpha(2)beta(3)gamma(2)gamma-aminobutyric acid(A) receptors.
2002,
Pubmed
Williams,
Gamma-aminobutyric acid increases the water accessibility of M3 membrane-spanning segment residues in gamma-aminobutyric acid type A receptors.
1999,
Pubmed
Yang,
Mechanisms of etomidate potentiation of GABAA receptor-gated currents in cultured postnatal hippocampal neurons.
1996,
Pubmed
Zhong,
Photo-activated azi-etomidate, a general anesthetic photolabel, irreversibly enhances gating and desensitization of gamma-aminobutyric acid type A receptors.
2008,
Pubmed
,
Xenbase
