RT Journal Article SR Electronic T1 The tarantula toxins ProTx-II and HWTX-IV differentially interact with human Nav1.7 voltage-sensors to inhibit channel activation and inactivation JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP mol.110.066332 DO 10.1124/mol.110.066332 A1 Yucheng Xiao A1 Kenneth M. Blumenthal A1 James O Jackson A1 Songping Liang A1 Theodore R Cummins YR 2010 UL http://molpharm.aspetjournals.org/content/early/2010/09/20/mol.110.066332.abstract AB The voltage-gated sodium channel Nav1.7 plays a crucial role in pain, and drugs that inhibit hNav1.7 may have tremendous therapeutic potential. ProTx-II and huwentoxin-IV (HWTX-IV), cystine knot peptides from tarantula venoms, preferentially block hNav1.7. Understanding the interactions of these toxins with sodium channels could aid the development of novel pain therapeutics. While both ProTx-II and HWTX-IV have been proposed to preferentially block hNav1.7 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 hNav1.7. The mutation E818C increases ProTx-II's and HWTX-IV's IC50 for block of hNav1.7 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. Importantly, we also show that ProTx-II, but not HWTX-IV, preferentially interacts with hNav1.7 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 IC50 for impairment of fast-inactivation by ~6-fold. In contrast mutations D1586A and F1592A in domain-IV increased ProTx-II's IC50 for impairment of fast-inactivation by ~4-fold. Our results show that 1) while ProTx-II and HWTX-IV binding determinants on domain-II may overlap, domain-II plays a much more crucial role for HWTX-IV and 2) 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 in order to influence sodium channel inactivation.