Recognition of inter‐transmembrane regions of acetylcholine receptor α subunit by antibodies, T cells and neurotoxins implications for membrane‐subunit organization

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Abstract
Three regions of the α chain of Torpedo californica acetylcholine receptor (AChR), corresponding to residues α262–276, α388–408 and α427–437 were synthesized, purified and characterized. The first two peptides have been proposed to occupy inter‐transmembrane regions while the third represented the C‐terminal segment, proposed by various models to be either extracellular or intracellular. Peptide α388–408 stimulated a good response in the AChR‐primed T cells of H‐2s haplotype mice, a low response in the H‐2q haplotype and no response in the H‐2b haplotype. Peptide α427–437 stimulated AChR‐primed T cells of the H‐2s haplotype, but caused no response in the q and b haplotypes. Peptide α262–276 evoked no in vitro stimulation in any of the s, q or b haplotypes. In antibody binding studies, peptide α388–408 bound antibodies raised against free AChR or against membrane‐bound AChR. The other two peptides showed little or no binding activity. Further, peptide α388–408 bound specifically both 125‐I‐labelled bungarotoxin and cobratoxin, while the other two peptides had no binding activity. These results were consistent with only one of the models for subunit organization with‐in the membrane.

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