title: Unanticipated structural and functional properties of delta-subunit-containing GABAA receptors.
abstract: GABA(A) receptors mediate inhibitory neurotransmission in the mammalian brain via synaptic and extrasynaptic receptors. The delta (delta)-subunit-containing receptors are expressed exclusively extra-synaptically and mediate tonic inhibition. In the present study, we were interested in determining the architecture of receptors containing the delta-subunit. To investigate this, we predefined the subunit arrangement by concatenation. We prepared five dual and three triple concatenated subunit constructs. These concatenated dual and triple constructs were used to predefine nine different GABA(A) receptor pentamers. These pentamers composed of alpha(1)-, beta(3)-, and delta-subunits were expressed in Xenopus oocytes and maximal currents elicited in response to 1 mm GABA were determined in the presence and absence of THDOC (3alpha, 21-dihydroxy-5alpha-pregnane-20-one). beta(3)-alpha(1)-delta/alpha(1)-beta(3) and beta(3)-alpha(1)-delta/beta(3)-alpha(1) resulted in the expression of large currents in response to GABA. Interestingly, the presence of the neurosteroid THDOC uncovered alpha(1)-beta(3)-alpha(1)/beta(3)-delta receptors, additionally. The functional receptors were characterized in detail using the agonist GABA, THDOC, Zn(2+), and ethanol and their properties were compared with those of non-concatenated alpha(1)beta(3) and alpha(1)beta(3)delta receptors. Each concatenated receptor isoform displayed a specific set of properties, but none of them responded to 30 mm ethanol. We conclude from the investigated receptors that delta can assume multiple positions in the receptor pentamer. The GABA dose-response properties of alpha(1)-beta(3)-alpha(1)/beta(3)-delta and beta(3)-alpha(1)-delta/alpha(1)-beta(3) match most closely the properties of non-concatenated alpha(1)beta(3)delta receptors. Furthermore, we show that the delta-subunit can contribute to the formation of an agonist site in alpha(1)-beta(3)-alpha(1)/beta(3)-delta receptors.
authors.affiliation: Institute of Biochemistry and Molecular Medicine, University of Bern, CH-3012 Bern, Switzerland.
authors.forename: Kuldeep H
authors.initials: KH
authors.lastname: Kaur
authors.forename: Roland
authors.initials: R
authors.lastname: Baur
authors.forename: Erwin
authors.initials: E
authors.lastname: Sigel
mesh_terms: D000818:Animals; D014151:Anti-Anxiety Agents / Q000494:pharmacology; D002492:Central Nervous System Depressants / Q000494:pharmacology; D003900:Desoxycorticosterone / Q000031:analogs & derivatives / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D000431:Ethanol; D018682:GABA Agents / Q000494:pharmacology; D018755:GABA Agonists / Q000494:pharmacology; D058785:GABA-A Receptor Agonists; D058787:GABA-A Receptor Antagonists; D015870:Gene Expression; D006801:Humans; D009865:Oocytes; D020836:Protein Structure, Quaternary / Q000235:genetics; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000819:agonists / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship; D014981:Xenopus; D015032:Zinc / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D014151:Anti-Anxiety Agents; D002492:Central Nervous System Depressants; D018682:GABA Agents; D018755:GABA Agonists; D058785:GABA-A Receptor Agonists; D058787:GABA-A Receptor Antagonists; D011963:Receptors, GABA-A; D011993:Recombinant Fusion Proteins; D000431:Ethanol; D003900:Desoxycorticosterone; C009413:tetrahydrodeoxycorticosterone; D005680:gamma-Aminobutyric Acid; D015032:Zinc