Alpha-A conotoxin PIVA is the major paralytic toxin found in the venom produced by the piscivorous snail Conus purpurascens. This peptide acts by blocking the acetylcholine binding site of the nicotinic acetylcholine receptor at the neuromuscular junction. The overall shape of the peptide is described as an "iron" with a highly charged hydrophilic loop of 15S-19R forming the "handle" domain that is exposed to the exterior of the protein. The stability of the conotoxin is primarily governed by three disulphide bonds. A triangular structural motif formed by residues 19R, 12H and 6Y is thought to constitute a "binding core" that is important in binding to the acetylcholine receptor.