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

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-2 s haplotype mice, a low response in the H-2 q haplotype and no response in the H-2 b haplotype. Peptide α427–437 stimulated AChR-primed T cells of the H-2 s 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.