Lethal neurotoxin. Selectively blocks tetrodotoxin-sensitive voltage-gated sodium channels (Nav). Does not affect tetrodotoxin-resistant voltage-gated sodium channels or calcium channels (By similarity). Monomer. Expressed by the venom gland. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. Belongs to the neurotoxin 10 (Hwtx-1) family. 15 (Hntx-3) subfamily. While it is structurally defined as a knottin it lacks the conserved Cys residue in position 64.