SignificanceVoltage-gated ion channels contain domains that have discrete functionalities. The central pore domain allows current flow and provides ion selectivity, whereas peripherally located voltage-sensing domains (VSDs) are needed for voltage-dependent gating. Certain mutations trigger a leak current through VSDs, known as gating pore current. Hypokalemic periodic paralysis (HypoPP) type 2 is caused by mutations in the skeletal muscle voltage-gated sodium channel NaV1.4 that neutralize positive charges in S4 voltage-sensing segments of VSDs. We show that Hm-3 toxin from the crab spider Heriaeus melloteei inhibits gating pore currents through such mutant channels. We propose that Hm-3 and similar toxins may constitute useful hits in developing gating pore current inhibitors and HypoPP therapy.

Background: Several toxins from mygalomorph spiders are known to inhibit sodium channel activation. Results: Hm-3 toxin from the araneomorph spider Heriaeus melloteei inhibits mammalian and insect sodium channel activation and possesses membrane activity. Conclusion: Hm-3 binds to sodium channel voltage sensors through membrane access. Significance: The first sodium channel activation inhibitor from Araneomorphae points to parallel evolution of H. melloteei and its distant mygalomorph relatives.