Isolation and structure-activity of mu-conotoxin TIIIA, a potent inhibitor of tetrodotoxin-sensitive voltage-gated sodium channels

Mol Pharmacol. 2007 Mar;71(3):676-85. doi: 10.1124/mol.106.028225. Epub 2006 Dec 1.


Mu-conotoxins are three-loop peptides produced by cone snails to inhibit voltage-gated sodium channels during prey capture. Using polymerase chain reaction techniques, we identified a gene sequence from the venom duct of Conus tulipa encoding a new mu-conotoxin-TIIIA (TIIIA). A 125I-TIIIA binding assay was established to isolate native TIIIA from the crude venom of Conus striatus. The isolated peptide had three post-translational modifications, including two hydroxyproline residues and C-terminal amidation, and <35% homology to other mu-conotoxins. TIIIA potently displaced [3H]saxitoxin and 125I-TIIIA from rat brain (Nav1.2) and skeletal muscle (Nav1.4) membranes. Alanine and glutamine scans of TIIIA revealed several residues, including Arg14, that were critical for high-affinity binding to tetrodotoxin (TTX)-sensitive Na+ channels. We were surprised to find that [E15A]TIIIA had a 10-fold higher affinity than TIIIA for TTX-sensitive sodium channels (IC50, 15 vs. 148 pM at rat brain membrane). TIIIA was selective for Nav1.2 and -1.4 over Nav1.3, -1.5, -1.7, and -1.8 expressed in Xenopus laevis oocytes and had no effect on rat dorsal root ganglion neuron Na+ current. 1H NMR studies revealed that TIIIA adopted a single conformation in solution that was similar to the major conformation described previously for mu-conotoxin PIIIA. TIIIA and analogs provide new biochemical probes as well as insights into the structure-activity of mu-conotoxins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Conotoxins / chemistry
  • Conotoxins / isolation & purification*
  • Conotoxins / pharmacology
  • Conus Snail
  • Female
  • Magnetic Resonance Spectroscopy
  • Molecular Sequence Data
  • Mollusk Venoms / analysis
  • Radioligand Assay
  • Rats
  • Sodium Channel Blockers / chemistry
  • Sodium Channel Blockers / isolation & purification*
  • Sodium Channel Blockers / pharmacology
  • Structure-Activity Relationship
  • Tetrodotoxin / pharmacology*
  • Xenopus laevis


  • Conotoxins
  • Mollusk Venoms
  • Sodium Channel Blockers
  • mu-conotoxin TIIIA, Conus tulipa
  • Tetrodotoxin