Binds irreversibly and specifically to M1 (CHRM1) muscarinic acetylcholine receptors, blocking further binding of antagonists and preventing the action of agonists. Monomer. Expressed by the venom gland. Contains 4 disulfide bonds. Is classified as a P-type cytotoxin, since a proline residue stands at position 33 (Pro-31 in standard classification). Belongs to the snake three-finger toxin family. Short-chain subfamily. Aminergic toxin sub-subfamily.