Neurotoxin certainly responsible of defensive persistent and painful stings of the giant stinging tree, since it provokes similar effects (PubMed:32938666). Acts by potently delaying voltage-gated sodium channel (Nav) inactivation in a concentration-dependent manner (EC(50)=4 nM) (PubMed:32938666). Mainly targets Nav1.7/SCN9A channels, since the two Nav1.7/SCN9A inhibitors tetrodotoxin and the spider toxin Pn3a potently reduce nocifensive behaviors it causes (By similarity). On the Nav1.7/SCN9A channel, this toxin causes a significant hyperpolarizing shift in the voltage dependence of activation, but has no significant effect on the voltage dependence of steady-state fast inactivation (PubMed:32938666). Its effects on Nav currents are irreversible, with no apparent reduction in activity even after repeated wash steps over 30 minutes (By similarity). In vivo, it causes nocifensive behavior in mice (licking or biting and shaking or lifting of the affected paw) lasting for approximately 1 hour (PubMed:32938666). Expressed in trichomes, that are stiff epidermal hairs located on the surface of petioles and leaves. Not expressed in other aerial parts. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. The name 'gympietide' is derived from the name in the Gubbi-Gubbi language for the stinging trees (gympie-gympie). Belongs to the gympietide family.