title: Immunochemical tests of acetylcholine receptor subunit models.
abstract: Acetylcholine receptors of fish electric organs and mammalian skeletal muscle comprise four structurally homologous glycoprotein subunits in the mole ratio alpha 2 beta gamma delta (refs 1-4). All four subunits have leader sequences and are exposed on both sides of the membrane. From amino acid sequencing, three groups have predicted that each subunit has four hydrophobic alpha-helical transmembranous domains. Because the N-terminus of each subunit is thought to remain on the extracellular surface after cleavage of the leader sequence, this model predicts that the N- and C- termini are both on the extracellular side. An alternative model proposed by two other groups predicts that there is, in addition, a fifth amphipathic transmembranous domain which would place the C-terminus on the cytoplasmic side. Here, using anti-subunit sera and monoclonal antibodies and their reaction with synthetic subunit peptides, we demonstrate that the C-terminus is in fact on the cytoplasmic surface. We also show that, contrary to other predictions, the most hydrophilic sequence on the extracellular domain of alpha-subunits is not the main immunogenic region.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000939:Epitopes; D046911:Macromolecular Substances; D008565:Membrane Proteins; D010446:Peptide Fragments / Q000276:immunology; D011487:Protein Conformation; D011978:Receptors, Nicotinic / Q000276:immunology; D012995:Solubility; D014101:Torpedo
chemical_list: D000939:Epitopes; D046911:Macromolecular Substances; D008565:Membrane Proteins; D010446:Peptide Fragments; D011978:Receptors, Nicotinic