Abstract
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. Whereas 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. It is noteworthy that 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 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.
Footnotes
↵ The online version of this article (available at http://molpharm.aspetjournals.org) contains supplemental material.
This work was supported by National Institutes of Health National Institute of Neurological Disorders and Stroke [Grants NS054642, NS053422]; the 973 Research Program of China [Contract 2010CB529800]; and the Program for New Century Excellent Talents in University [Contract NCET-07-0279].
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.110.066332.
-
ABBREVIATIONS:
- HWTX-IV
- huwentoxin-IV
- TTX
- tetrodotoxin
- WT
- wild type
- HEK
- human embryonic kidney
- DI
- domain I
- DII
- domain II
- DIII
- domain III
- DIV
- domain IV
- S
- transmembrane segment.
- Received May 12, 2010.
- Accepted September 20, 2010.
- Copyright © 2010 The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|