Molecular interactions of the gating modifier toxin ProTx-II with Na v1.5: Implied existence of a novel toxin binding site coupled to activation

Jaime J. Smith, Theodore R. Cummins, Sujith Alphy, Kenneth M. Blumenthal

Research output: Contribution to journalArticle

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Abstract

Voltage-gated Na+ channels are critical components in the generation of action potentials in excitable cells, but despite numerous structure-function studies on these proteins, their gating mechanism remains unclear. Peptide toxins often modify channel gating, thereby providing a great deal of information about these channels. ProTx-II is a 30-amino acid peptide toxin from the venom of the tarantula, Thrixopelma pruriens, that conforms to the inhibitory cystine knot motif and which modifies activation kinetics of Nav and Cav, but not Kv, channels. ProTx-II inhibits current by shifting the voltage dependence of activation to more depolarized potentials and, therefore, differs from the classic site 4 toxins that shift voltage dependence of activation in the opposite direction. Despite this difference in functional effects, ProTx-II has been proposed to bind to neurotoxin site 4 because it modifies activation. Here, we investigate the bioactive surface of ProTx-II by alanine-scanning the toxin and analyzing the interactions of each mutant with the cardiac isoform, Nav1.5. The active face of the toxin is largely composed of hydrophobic and cationic residues, joining a growing group of predominantly Kv channel gating modifier toxins that are thought to interact with the lipid environment. In addition, we performed extensive mutagenesis of Nav1.5 to locate the receptor site with which ProTx-II interacts. Our data establish that, contrary to prior assumptions, ProTx-II does not bind to the previously characterized neurotoxin site 4, thus making it a novel probe of activation gating in Na v channels with potential to shed new light on this process.

Original languageEnglish (US)
Pages (from-to)12687-12697
Number of pages11
JournalJournal of Biological Chemistry
Volume282
Issue number17
DOIs
StatePublished - Apr 27 2007

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ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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