Oligomeric structure of muscarinic receptors is shown by photoaffinity labeling: subunit assembly may explain high- and low-affinity agonist states.
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.
D000345:Affinity Labels; D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000378:metabolism; D001923:Brain Chemistry; D046911:Macromolecular Substances; D008297:Male; D011487:Protein Conformation; D051381:Rats; D011950:Receptors, Cholinergic / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000378:metabolism; D013329:Structure-Activity Relationship
D000345:Affinity Labels; D046911:Macromolecular Substances; D011950:Receptors, Cholinergic; D011976:Receptors, Muscarinic