Mapping general anesthetic binding site(s) in human ?1?3 ?-aminobutyric acid type A receptors with [³H]TDBzl-etomidate, a photoreactive etomidate analogue.

ABSTRACT: The ?-aminobutyric acid type A receptor (GABA(A)R) is a target for general anesthetics of diverse chemical structures, which act as positive allosteric modulators at clinical doses. Previously, in a heterogeneous mixture of GABA(A)Rs purified from bovine brain, [³H]azietomidate photolabeling of ?Met-236 and ?Met-286 in the ?M1 and ?M3 transmembrane helices identified an etomidate binding site in the GABA(A)R transmembrane domain at the interface between the ? and ? subunits [Li, G. D., et.al. (2006) J. Neurosci. 26, 11599-11605]. To further define GABA(A)R etomidate binding sites, we now use [³H]TDBzl-etomidate, an aryl diazirine with broader amino acid side chain reactivity than azietomidate, to photolabel purified human FLAG-?1?3 GABA(A)Rs and more extensively identify photolabeled GABA(A)R amino acids. [³H]TDBzl-etomidate photolabeled in an etomidate-inhibitable manner ?3Val-290, in the ?3M3 transmembrane helix, as well as ?1Met-236 in ?1M1, a residue photolabeled by [³H]azietomidate, while no photolabeling of amino acids in the ?M2 and ?M2 helices that also border the etomidate binding site was detected. The location of these photolabeled amino acids in GABA(A)R homology models derived from the recently determined structures of prokaryote (GLIC) or invertebrate (GluCl) homologues and the results of computational docking studies predict the orientation of [³H]TDBzl-etomidate bound in that site and the other amino acids contributing to this GABA(A)R intersubunit etomidate binding site. Etomidate-inhibitable photolabeling of ?3Met-227 in ?M1 by [³H]TDBzl-etomidate and [³H]azietomidate also provides evidence of a homologous etomidate binding site at the ?3-?3 subunit interface in the ?1?3 GABA(A)R.

SUBMITTER: Chiara DC 

PROVIDER: S-EPMC3274767 | biostudies-literature | 2012 Jan

REPOSITORIES: biostudies-literature