Stoichiometry for α-bungarotoxin block of α7 acetylcholine receptors.
α-Bungarotoxin (α-Btx) binds to the five agonist binding sites on the homopentameric α7-acetylcholine receptor, yet the number of bound α-Btx molecules required to prevent agonist-induced channel opening remains unknown. To determine the stoichiometry for α-Btx blockade, we generate receptors comprised of wild-type and α-Btx-resistant subunits, tag one of the subunit types with conductance mutations to report subunit stoichiometry, and following incubation with α-Btx, monitor opening of individual receptor channels with defined subunit stoichiometry. We find that a single α-Btx-sensitive subunit confers nearly maximal suppression of channel opening, despite four binding sites remaining unoccupied by α-Btx and accessible to the agonist. Given structural evidence that α-Btx locks the agonist binding site in an inactive conformation, we conclude that the dominant mechanism of antagonism is non-competitive, originating from conformational arrest of the binding sites, and that the five α7 subunits are interdependent and maintain conformational symmetry in the open channel state.
Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, Minnesota 55905, USA.
Corrie J B
CJ
daCosta
Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, Minnesota 55905, USA.
Chris R
CR
Free
1] Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, Minnesota 55905, USA [2] Department of Neurology, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, Minnesota 55905, USA.
Steven M
SM
Sine
D001665:Binding Sites; D002038:Bungarotoxins / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D057809:HEK293 Cells; D006801:Humans; D007457:Iodine Radioisotopes; D007700:Kinetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D064569:alpha7 Nicotinic Acetylcholine Receptor / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism
D002038:Bungarotoxins; D007457:Iodine Radioisotopes; D064569:alpha7 Nicotinic Acetylcholine Receptor