Synthesis, Solution Structure, and Phylum Selectivity of a Spider δ-Toxin That Slows Inactivation of Specific Voltage-gated Sodium Channel Subtypes

• Published in: The Journal of biological chemistry 2009-09, Vol.284 (36), p.24568-24582
• Main Authors: Yamaji, Nahoko, Little, Michelle J., Nishio, Hideki, Billen, Bert, Villegas, Elba, Nishiuchi, Yuji, Tytgat, Jan, Nicholson, Graham M., Corzo, Gerardo
• Format: Article
• Language: English
• Subjects: Animals; Insect Proteins - antagonists & inhibitors; Insect Proteins - metabolism; Mechanisms of Signal Transduction; NAV1.1 Voltage-Gated Sodium Channel; NAV1.3 Voltage-Gated Sodium Channel; NAV1.6 Voltage-Gated Sodium Channel; Nerve Tissue Proteins - antagonists & inhibitors; Nerve Tissue Proteins - metabolism; Neurons - metabolism; Nuclear Magnetic Resonance, Biomolecular; Periplaneta - metabolism; Protein Structure, Tertiary; Rats; Sodium Channels - metabolism; Spider Venoms - chemistry; Spider Venoms - pharmacology; Xenopus laevis
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M109.030841

Magi 4, now renamed δ-hexatoxin-Mg1a, is a 43-residue neurotoxic peptide from the venom of the hexathelid Japanese funnel-web spider (Macrothele gigas) with homology to δ-hexatoxins from Australian funnel-web spiders. It binds with high affinity to receptor site 3 on insect voltage-gated sodium (NaV) channels but, unlike δ-hexatoxins, does not compete for the related site 3 in rat brain despite being previously shown to be lethal by intracranial injection. To elucidate differences in NaV channel selectivity, we have undertaken the first characterization of a peptide toxin on a broad range of mammalian and insect NaV channel subtypes showing that δ-hexatoxin-Mg1a selectively slows channel inactivation of mammalian NaV1.1, NaV1.3, and NaV1.6 but more importantly shows higher affinity for insect NaV1 (para) channels. Consequently, δ-hexatoxin-Mg1a induces tonic repetitive firing of nerve impulses in insect neurons accompanied by plateau potentials. In addition, we have chemically synthesized and folded δ-hexatoxin-Mg1a, ascertained the bonding pattern of the four disulfides, and determined its three-dimensional solution structure using NMR spectroscopy. Despite modest sequence homology, we show that key residues important for the activity of scorpion α-toxins and δ-hexatoxins are distributed in a topologically similar manner in δ-hexatoxin-Mg1a. However, subtle differences in the toxin surfaces are important for the novel selectivity of δ-hexatoxin-Mg1a for certain mammalian and insect NaV channel subtypes. As such, δ-hexatoxin-Mg1a provides us with a specific tool with which to study channel structure and function and determinants for phylum- and tissue-specific activity.