Psi-conotoxins act on postsynaptic membranes, and act as non-competitive antagonist of nicotinic acetylcholine receptors (nAChR). Is less toxic than Psi-conotoxin PIIIE. Expressed by the venom duct. The cysteine framework is III (CC-C-C-CC). Classified in the M-4 branch, since 4 residues stand between the fourth and the fifth cysteine residues. Belongs to the conotoxin M superfamily.