Oligomeric Structure of Muscarinic Receptors is Shown by Photoaffinity Labeling: Subunit Assembly May Explain High- and Low-Affinity Agonist States

• Published in: Proceedings of the National Academy of Sciences - PNAS 1983-01, Vol.80 (1), p.156-159
• Main Authors: Avissar, Sofia, Amitai, Gabriel, Sokolovsky, Mordechai
• Format: Article
• Language: English
• Subjects: acetylcholine; Affinity Labels; Agonists; Animals; Binding Sites; Biochemistry; brain; Brain - metabolism; Brain Chemistry; Cerebellum; Dimers; Electrophoresis; Gels; heart; Ligands; Macromolecular Substances; Male; Muscarinic receptors; N-methyl-4-piperidyl p-azidobenzilate; photoaffinity labelling; Protein Conformation; Radioactive decay; Rats; Receptors; Receptors, Cholinergic - metabolism; Receptors, Muscarinic - metabolism; Structure-Activity Relationship
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.80.1.156

The potent muscarinic photoaffinity reagent N-methyl-4-piperidyl p-azidobenzilate (azido-4NMPB) was used to covalently label specific muscarinic binding sites in various brain regions and in the heart. In the cortex and hippocampus, a single specifically labeled protein with an apparent molecular mass of 86,000 daltons was detected by gel electrophoresis. In the medulla pons, cerebellum, and cardiac atria, there was a 160,000-dalton band in addition to the 86,000-dalton polypeptide. Under certain conditions, alkali or hydroxylamine treatment dissociated both macromolecules into a single 40,000-dalton polypeptide. These results suggest that the muscarinic receptor exists in oligomeric forms and that a dimer and tetramer of a basic 40,000-dalton peptide may exist as interconvertible species. We propose a model to explain the biological architecture of the muscarinic receptors and suggest a possible correlation between the azido-4NMPB-labeled polypeptides and the two states of the receptor observed in agonist binding experiments.