title: A comparison of glycine- and ivermectin-mediated conformational changes in the glycine receptor ligand-binding domain.
abstract: Glycine receptor chloride channels are Cys-loop receptor proteins that isomerize between a low affinity closed state and a high affinity ion-conducting state. There is currently much interest in understanding the mechanisms that link affinity changes with conductance changes. This essentially involves an agonist binding in the glycine receptor ligand-binding site initiating local conformational changes that propagate in a wave towards the channel gate. However, it has proved difficult to convincingly distinguish those agonist-induced domain movements that are critical for triggering activation from those that are simply local deformations to accommodate ligands in the site. We employed voltage-clamp fluorometry to compare conformational changes in the ligand-binding site in response to activation by glycine, which binds locally, and ivermectin, which binds in the transmembrane domain. We reasoned that ivermectin-mediated activation should initiate a conformational wave that propagates from the pore-lining domain towards the ligand-binding domain, eliciting conformational changes in those extracellular domains that are allosterically linked to the gate. We found that ivermectin indeed elicited conformational changes in ligand-binding domain loops C, D and F. This implies that conformational changes in these domains are important for activation. This result also provides a mechanism to explain how ivermectin potentiates glycine-induced channel activation.
authors.affiliation: Queensland Brain Institute and School of Biomedical Sciences, University of Queensland, Brisbane, QLD 4072, Australia.
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Lynch
mesh_terms: D000818:Animals; D005470:Fluorometry; D005998:Glycine / Q000378:metabolism / Q000494:pharmacology*; D007559:Ivermectin / Q000494:pharmacology*; D008024:Ligands; D018408:Patch-Clamp Techniques; D017434:Protein Structure, Tertiary / Q000187:drug effects; D051381:Rats; D018009:Receptors, Glycine / Q000737:chemistry*; D014982:Xenopus laevis / Q000378:metabolism
chemical_list: D008024:Ligands; D018009:Receptors, Glycine; D007559:Ivermectin; D005998:Glycine