Enhances the high-affinity desensitization of human P2RX3 purinoceptors. Expressed by the venom gland. The toxin is composed of 2 domains: a highly rigid N-terminal inhibitor cystine knot (knottin) domain and a rather flexible C-terminal linear cationic cytotoxin domain that forms amphiphilic alpha-helices. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. Belongs to the neurotoxin 19 (CSTX) family. 05 (U4-Lctx) subfamily.