TY - JOUR T1 - Isolation and Structure-Activity of μ-Conotoxin TIIIA, A Potent Inhibitor of Tetrodotoxin-Sensitive Voltage-Gated Sodium Channels JF - Molecular Pharmacology JO - Mol Pharmacol SP - 676 LP - 685 DO - 10.1124/mol.106.028225 VL - 71 IS - 3 AU - Richard J. Lewis AU - Christina I. Schroeder AU - Jenny Ekberg AU - Katherine J. Nielsen AU - Marion Loughnan AU - Linda Thomas AU - Denise A. Adams AU - Roger Drinkwater AU - David J. Adams AU - Paul F. Alewood Y1 - 2007/03/01 UR - http://molpharm.aspetjournals.org/content/71/3/676.abstract N2 - μ-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 μ-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 μ-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 μ-conotoxin PIIIA. TIIIA and analogs provide new biochemical probes as well as insights into the structure-activity of μ-conotoxins. The American Society for Pharmacology and Experimental Therapeutics ER -