Inhibits P2RX3 receptors. Has an analgesic effect in rat. Enhances the high-affinity desensitization of P2RX3 receptors. At 50 nM, decreases the IC(50) for ambient ATP from 46.5 nM to 12.7 nM in mouse P2RX3. Expressed by the venom gland. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. Does not affect mouse P2RX2 or P2RX2/P2RX3 receptors. Belongs to the neurotoxin 33 family.