Mu-conotoxins block voltage-gated sodium channels (Nav). This toxin shows potent activity on Nav1.4/SCN4A (IC(50)=286 nM), and weak activity on mNav1.6/SCN8A. 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. Does not show activity when tested (1 uM) on rNav1.2/SCN2A, hNav1.5/SCN7A, hNav1.7/SCN9A and hNav1.8/ SCN10A. Both the Thr-5-hydroxypro-6 and Lys-16-hydroxypro-17 peptide bonds are in trans conformations, whereas the hydroxypro-6-hydroxypro-7 bond adopts a cis conformation. Belongs to the conotoxin M superfamily.