Location of ligand-binding sites on the nicotinic acetylcholine receptor alpha-subunit

• Published in: The Journal of biological chemistry Vol. 261; no. 29; pp. 13735 - 13743
• Main Authors: Pedersen, S E, Dreyer, E B, Cohen, J B
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 15.10.1986; American Society for Biochemistry and Molecular Biology
• Subjects: Acetylglucosaminidase; Animals; Binding Sites; Biological and medical sciences; Cell physiology; Concanavalin A - analogs & derivatives; Electric Organ - metabolism; Endopeptidases; Fluorescein-5-isothiocyanate - analogs & derivatives; Fluoresceins; Fundamental and applied biological sciences. Psychology; Ligands; Macromolecular Substances; Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; Metalloendopeptidases; Molecular and cellular biology; Neurotransmission; Peptide Mapping; Receptors, Nicotinic - isolation & purification; Receptors, Nicotinic - metabolism; Serine Endopeptidases; Torpedo; Vertebrata; Cholinergic receptor; Amine; Molecular structure; Allosteric site; Pisces; Animal; Torpedo californica; Aromatic compound; Binding site; Chemical labelling; Nicotinic receptor
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)67082-6

The portions of the Torpedo californica nicotinic acetylcholine receptor (AChR) alpha-subunit that contribute to the allosteric antagonist-binding site and to the agonist-binding site have been localized by affinity labeling and proteolytic mapping. [3H]Meproadifen mustard was employed as an affinity label for the allosteric antagonist-binding site and [3H]tubocurare as a photoaffinity label for the agonist-binding site. Both labels were found in a 20-kDa proteolytic fragment generated from the AChR alpha-subunit by Staphylococcus aureus V8 protease. This 20-kDa peptide also contains the 3H-labeled 4-(N-maleimido)-alpha-benzyltrimethylammonium iodide-reactive site and binds 125I-alpha-bungarotoxin. N-terminal sequencing established that the 20-kDa fragment began at Ser-173 of the alpha-subunit. Fluorescein isothiocyanate-conjugated concanavalin A could be bound to the second of the two major V8 cleavage products, an 18-kDa peptide. This peptide was also sensitive to treatment with endo-beta-N-acetyl-glucosaminidase H, consistent with the presence of N-linked carbohydrate on this fragment. The N terminus of this peptide was found to be Val-46 of the alpha-subunit sequence. Experiments designed to map disulfide bonds within the AChR alpha-subunit indicate that no bonds exist between the 18-kDa fragment (containing Cys-128 and Cys-142) and the 20-kDa fragment (containing Cys-192, Cys-193, and Cys-222). These results establish that the 20-kDa fragment contributes to both the acetylcholine and the allosteric antagonist-binding sites, whereas there is no evidence that the 18-kDa fragment is part of either site.