title: Investigating the Role of Loop C Hydrophilic Residue 'T244' in the Binding Site of ρ1 GABAC Receptors via Site Mutation and Partial Agonism.
abstract: The loop C hydrophilic residue, threonine 244 lines the orthosteric binding site of ρ1 GABAC receptors was studied by point mutation into serine, alanine and cysteine, and tested with GABA, some representative partial agonists and antagonists. Thr244 has a hydroxyl group essential for GABA activity that is constrained by the threonine methyl group, orienting it toward the binding site. Significant decreases in activation effects of the studied ligands at ρ1 T244S mutant receptors, suggests a critical role for this residue. Results of aliphatic and heteroaromatic partial agonists demonstrate different pharmacological effects at ρ1 T244S mutant receptors when co-applied with GABA EC50 responses. ρ1 T244A and ρ1 T244C mutant receptors have minimal sensitivity to GABA at high mM concentrations, whereas, the ρ1 WT partial agonists, β-alanine and MTSEA demonstrate more efficacy and potency, respectively, than GABA at these mutant receptors. This study explores the role of Thr244 in the binding of agonists as an initial step during channel gating by moving loop C towards the ligand.
authors.affiliation: Faculty of Pharmacy, University of Sydney, Sydney, NSW, Australia.
authors.forename: Moawiah M
authors.initials: MM
authors.lastname: Naffaa
authors.affiliation: Faculty of Pharmacy, University of Sydney, Sydney, NSW, Australia.
authors.forename: Nathan
authors.initials: N
authors.lastname: Absalom
authors.affiliation: Faculty of Pharmacy, University of Sydney, Sydney, NSW, Australia.
authors.forename: V Raja
authors.initials: VR
authors.lastname: Solomon
authors.affiliation: Faculty of Pharmacy, University of Sydney, Sydney, NSW, Australia.
authors.forename: Mary
authors.initials: M
authors.lastname: Chebib
authors.affiliation: Faculty of Pharmacy, University of Sydney, Sydney, NSW, Australia.
authors.forename: David E
authors.initials: DE
authors.lastname: Hibbs
authors.affiliation: Faculty of Pharmacy, University of Sydney, Sydney, NSW, Australia.
authors.forename: Jane R
authors.initials: JR
authors.lastname: Hanrahan
mesh_terms: D000595:Amino Acid Sequence / Q000235:genetics; D021542:Amino Acids, Neutral / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D018755:GABA Agonists / Q000494:pharmacology*; D018756:GABA Antagonists / Q000494:pharmacology*; D005998:Glycine / Q000494:pharmacology; D006801:Humans; D007539:Isonicotinic Acids / Q000494:pharmacology; D058446:Ligand-Gated Ion Channels / Q000378:metabolism*; D062105:Molecular Docking Simulation; D018408:Patch-Clamp Techniques; D017354:Point Mutation / Q000235:genetics; D011487:Protein Conformation; D018079:Receptors, GABA / Q000235:genetics* / Q000378:metabolism; D014982:Xenopus laevis; D015091:beta-Alanine / Q000494:pharmacology
chemical_list: D021542:Amino Acids, Neutral; D018755:GABA Agonists; D018756:GABA Antagonists; C087200:GABA-C receptor; D007539:Isonicotinic Acids; D058446:Ligand-Gated Ion Channels; D018079:Receptors, GABA; D015091:beta-Alanine; C013809:5-aminovaleric acid; D005998:Glycine; C015300:isoguvacine