Antibodies to synthetic peptides as probes of acetylcholine receptor structure

Peptides containing the C-terminus of the alpha-chain of the nicotinic acetylcholine receptor (nAChR), as deduced from cDNA data, were synthesised and shown to bind to antibodies to denatured nAChR. Conversely, peptide-specific antibodies bound both to native and to denatured nAChR. Binding was exclusively to the alpha-chain. Trypsinization experiments and the use of the unique C-terminal hexapeptide of the alpha-chain demonstrated that the proposed C-terminus does exist on the mature alpha-chain, and that post-translational cleavage can be discounted as an explanation of the discrepancy of the molecular masses of the alpha-chain deduced from SDS gel electrophoresis (40 kDa) and from the DNA sequencing (50 kDa). Cleavage of the alpha-chain in the membrane occurs at two closely linked sites, resulting in the formation of a large fragment (approximately 35 kDa) and the remainder of the chain (approximately 9-10 kDa). No signs of experimental myasthenia gravis were observed in rabbits immunised with C-terminal peptide coupled to carrier protein.