title: The tarantula toxins ProTx-II and huwentoxin-IV differentially interact with human Nav1.7 voltage sensors to inhibit channel activation and inactivation.
abstract: The voltage-gated sodium channel Na(v)1.7 plays a crucial role in pain, and drugs that inhibit hNa(v)1.7 may have tremendous therapeutic potential. ProTx-II and huwentoxin-IV (HWTX-IV), cystine knot peptides from tarantula venoms, preferentially block hNa(v)1.7. Understanding the interactions of these toxins with sodium channels could aid the development of novel pain therapeutics. Whereas both ProTx-II and HWTX-IV have been proposed to preferentially block hNa(v)1.7 activation by trapping the domain II voltage-sensor in the resting configuration, we show that specific residues in the voltage-sensor paddle of domain II play substantially different roles in determining the affinities of these toxins to hNa(v)1.7. The mutation E818C increases ProTx-II's and HWTX-IV's IC(50) for block of hNa(v)1.7 currents by 4- and 400-fold, respectively. In contrast, the mutation F813G decreases ProTx-II affinity by 9-fold but has no effect on HWTX-IV affinity. It is noteworthy that we also show that ProTx-II, but not HWTX-IV, preferentially interacts with hNa(v)1.7 to impede fast inactivation by trapping the domain IV voltage-sensor in the resting configuration. Mutations E1589Q and T1590K in domain IV each decreased ProTx-II's IC(50) for impairment of fast inactivation by ~6-fold. In contrast mutations D1586A and F1592A in domain-IV increased ProTx-II's IC(50) for impairment of fast inactivation by ~4-fold. Our results show that whereas ProTx-II and HWTX-IV binding determinants on domain-II may overlap, domain II plays a much more crucial role for HWTX-IV, and contrary to what has been proposed to be a guiding principle of sodium channel pharmacology, molecules do not have to exclusively target the domain IV voltage-sensor to influence sodium channel inactivation.
authors.affiliation: Department of Pharmacology and Toxicology, Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
authors.forename: Yucheng
authors.initials: Y
authors.lastname: Xiao
authors.forename: Kenneth
authors.initials: K
authors.lastname: Blumenthal
authors.forename: James O
authors.initials: JO
authors.lastname: Jackson
authors.forename: Songping
authors.initials: S
authors.lastname: Liang
authors.forename: Theodore R
authors.initials: TR
authors.lastname: Cummins
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008969:Molecular Sequence Data; D062556:NAV1.7 Voltage-Gated Sodium Channel; D026941:Sodium Channel Blockers / Q000378:metabolism* / Q000494:pharmacology; D015222:Sodium Channels / Q000378:metabolism*; D013111:Spider Venoms / Q000378:metabolism* / Q000494:pharmacology; D013112:Spiders
chemical_list: D062556:NAV1.7 Voltage-Gated Sodium Channel; C470626:ProTx-II peptide; C486866:SCN9A protein, human; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D013111:Spider Venoms; C470632:huwentoxin IV, Selenocosmia huwena