Snake toxin domain, present in short and long neurotoxins, cytotoxins and short toxins, and in other miscellaneous venom peptides. The toxin acts by binding to the nicotinic acetylcholine receptors in the postsynaptic membrane of skeletal muscles and preventing the binding of acetylcholine, thereby blocking the excitation of muscles. This domain contains 60-75 amino acids that are fixed by 4-5 disulfide bridges and is nearly all beta sheet; it exists as either monomers or dimers.