Synthetic peptides used to locate the .alpha.-bungarotoxin binding site and immunogenic regions on .alpha. subunits of the nicotinic acetylcholine receptor

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Abstract
Synthetic peptides corresponding to 57% of the sequence of .alpha. subunits of acetylcholine receptors from Torpedo californica electric organ and extending from the NH2 to the COOCH terminus have been synthesized. The .alpha.-bungarotoxin binding site on denatured .alpha. subunits was mapped within the sequence .alpha.185-199 by assaying binding of 125I-.alpha.-bungarotoxin to slot blots of synthetic peptides. Further studies showed that residues in the sequence .alpha.190-194, especially cysteines-.alpha.192,193, were critical for binding .alpha.-bungarotoxin. Reduction and alkylation studies suggested that these cysteines must be disulfide linked for .alpha.-bungarotoxin to bind. Binding sites for serum antibodies to native receptors or .alpha. subunits were mapped by indirect immunoprecipitation of 125I-peptides. Several antigenic sequences were identified, but a synthetic peptide corresponding to the main immunogenic region (which is highly conformation dependent) was not identified.

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