Structural models of the nicotinic acetylcholine receptor and its toxin-binding sites.

Models of the protein structure of agonist-, competitive antagonist-, and snake neurotoxin-binding sites were designed using the sequence of the first 54 residues of the acetylcholine receptor (AChR) alpha subunit from Torpedo californica. These models are based on the premise that the N-terminal portions of the subunits form the outermost extracellular surface of the AChR and that agonists bind to this portion. The models were developed by predicting the secondary structure of the alpha-subunit N-terminal segment from its sequence, then using these predictions to fold the segment into tertiary structures that should bind snake neurotoxins, agonists, and antagonists. Possible gating mechanisms and quaternary structures are suggested by the proposed tertiary structures of the subunits. Experiments are suggested to test aspects of the models.