Four novel tarantula toxins as selective modulators of voltage-gated sodium channel subtypes

Four novel peptide toxins that act on voltage-gated sodium channels have been isolated from tarantula venoms: ceratotoxins 1, 2, and 3 (CcoTx1, CcoTx2, and CcoTx3) from Ceratogyrus cornuatus and phrixotoxin 3 (PaurTx3) from Phrixotrichus auratus. The pharmacological profiles of these new toxins were characterized by electrophysiological measurements on six cloned voltage-gated sodium channel subtypes expressed in Xenopus laevis oocytes (Na(v)1.1/beta(1), Na(v)1.2/beta(1), Na(v)1.3/beta(1), Na(v)1.4/beta(1), Na(v)1.5/beta(1), and Na(v)1.8/beta(1)). These novel toxins modulate voltage-gated sodium channels with properties similar to those of typical gating-modifier toxins, both by causing a depolarizing shift in gating kinetics and by blocking the inward component of the sodium current. PaurTx3 is one of the most potent peptide modulators of voltage-gated sodium channels described thus far from spider venom, modulating Na(v)1.2 with an IC(50) value of 0.6 +/- 0.1 nM. CcoTx1 and CcoTx2, differing by only one amino acid, are potent modulators of different voltage-gated sodium channel subtypes from the central nervous system, except for Na(v)1.3, which is only affected by CcoTx2. The potency of CcoTx3 is lower, although this toxin seems to be more selective for the tetrodotoxin-resistant channel subtype Na(v)1.5/beta(1) (IC(50) = 447 +/- 32 nM). In addition to these results, molecular modeling indicates that subtle differences in toxin surfaces may relate to their different pharmacological profiles. Furthermore, an evolutionary trace analysis of these toxins and other structurally related three-disulfide spider toxins provides clues for the exploration of toxin-channel interaction and future structure-function research.