Synthesis, solution structure, and phylum selectivity of a spider delta-toxin that slows inactivation of specific voltage-gated sodium channel subtypes.
Magi 4, now renamed delta-hexatoxin-Mg1a, is a 43-residue neurotoxic peptide from the venom of the hexathelid Japanese funnel-web spider (Macrothele gigas) with homology to delta-hexatoxins from Australian funnel-web spiders. It binds with high affinity to receptor site 3 on insect voltage-gated sodium (Na(V)) channels but, unlike delta-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 Na(V) channel selectivity, we have undertaken the first characterization of a peptide toxin on a broad range of mammalian and insect Na(V) channel subtypes showing that delta-hexatoxin-Mg1a selectively slows channel inactivation of mammalian Na(V)1.1, Na(V)1.3, and Na(V)1.6 but more importantly shows higher affinity for insect Na(V)1 (para) channels. Consequently, delta-hexatoxin-Mg1a induces tonic repetitive firing of nerve impulses in insect neurons accompanied by plateau potentials. In addition, we have chemically synthesized and folded delta-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 alpha-toxins and delta-hexatoxins are distributed in a topologically similar manner in delta-hexatoxin-Mg1a. However, subtle differences in the toxin surfaces are important for the novel selectivity of delta-hexatoxin-Mg1a for certain mammalian and insect Na(V) channel subtypes. As such, delta-hexatoxin-Mg1a provides us with a specific tool with which to study channel structure and function and determinants for phylum- and tissue-specific activity.
Yamaji
Nahoko
N
Suntory Institute for Bioorganic Research, Mishima-gun, Shimamoto-cho, Osaka 618-8503, Japan.
Little
Michelle J
MJ
Nishio
Hideki
H
Billen
Bert
B
Villegas
Elba
E
Nishiuchi
Yuji
Y
Tytgat
Jan
J
Nicholson
Graham M
GM
Corzo
Gerardo
G
D000818:Animals; D019476:Insect Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D062550:NAV1.1 Voltage-Gated Sodium Channel; D062552:NAV1.3 Voltage-Gated Sodium Channel; D062557:NAV1.6 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D019906:Nuclear Magnetic Resonance, Biomolecular; D010526:Periplaneta / Q000378:metabolism; D017434:Protein Structure, Tertiary; D051381:Rats; D015222:Sodium Channels / Q000378:metabolism*; D013111:Spider Venoms / Q000737:chemistry* / Q000494:pharmacology*; D014982:Xenopus laevis
D019476:Insect Proteins; D062550:NAV1.1 Voltage-Gated Sodium Channel; D062552:NAV1.3 Voltage-Gated Sodium Channel; D062557:NAV1.6 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins; C568250:Scn1a protein, rat; C478638:Scn3a protein, rat; C507811:Scn8a protein, rat; D015222:Sodium Channels; D013111:Spider Venoms