title: Structural determinants for antagonist pharmacology that distinguish the rho1 GABAC receptor from GABAA receptors.
abstract: GABA receptor (GABAR) types C (GABACR) and A (GABAAR) are both GABA-gated chloride channels that are distinguished by their distinct competitive antagonist properties. The structural mechanism underlying these distinct properties is not well understood. In this study, using previously identified binding residues as a guide, we made individual or combined mutations of nine binding residues in the rho1 GABACR subunit to their counterparts in the alpha1beta2gamma2 GABAAR or reverse mutations in alpha1 or beta2 subunits. The mutants were expressed in Xenopus laevis oocytes and tested for sensitivities of GABA-induced currents to the GABAA and GABAC receptor antagonists. The results revealed that bicuculline insensitivity of the rho1 GABACR was mainly determined by Tyr106, Phe138 and Phe240 residues. Gabazine insensitivity of the rho1 GABACR was highly dependent on Tyr102, Tyr106, and Phe138. The sensitivity of the rho1 GABACR to 3-aminopropyl-phosphonic acid and its analog 3-aminopropyl-(methyl)phosphinic acid mainly depended on residues Tyr102, Val140, FYS240-242, and Phe138. Thus, the residues Tyr102, Tyr106, Phe138, and Phe240 in the rho1 GABACR are major determinants for its antagonist properties distinct from those in the GABAAR. In addition, Val140 in the GABACR contributes to 3-APA binding. In conclusion, we have identified the key structural elements underlying distinct antagonist properties for the GABACR. The mechanistic insights were further extended and discussed in the context of antagonists docking to the homology models of GABAA or GABAC receptors.
authors.affiliation: Division of Neurobiology, Barrow Neurological Institute, 350 West Thomas Road, Phoenix, AZ 85013, USA.
authors.forename: Jianliang
authors.initials: J
authors.lastname: Zhang
authors.forename: Fenqin
authors.initials: F
authors.lastname: Xue
authors.forename: Yongchang
authors.initials: Y
authors.lastname: Chang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D001665:Binding Sites; D018118:Chloride Channels / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D005260:Female; D018756:GABA Antagonists / Q000494:pharmacology*; D058787:GABA-A Receptor Antagonists; D006801:Humans; D006860:Hydrogen Bonding; D020128:Inhibitory Concentration 50; D007700:Kinetics; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D063065:Organophosphonates / Q000494:pharmacology; D009943:Organophosphorus Compounds / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010721:Phosphinic Acids / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011724:Pyridazines / Q000494:pharmacology; D051381:Rats; D018079:Receptors, GABA / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011963:Receptors, GABA-A / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012680:Sensitivity and Specificity; D017386:Sequence Homology, Amino Acid; D014982:Xenopus laevis / Q000378:metabolism
chemical_list: D018118:Chloride Channels; D018756:GABA Antagonists; D058787:GABA-A Receptor Antagonists; C528239:Gabrr1 protein, rat; D008024:Ligands; D063065:Organophosphonates; D009943:Organophosphorus Compounds; D010721:Phosphinic Acids; D021122:Protein Subunits; D011724:Pyridazines; D018079:Receptors, GABA; D011963:Receptors, GABA-A; C523978:rho1 GABA(C) receptor, human; C068457:3-aminopropyl(methyl)phosphinic acid; C049853:gabazine; D001640:Bicuculline