A spider toxin that induces a typical effect of scorpion alpha-toxins but competes with beta-toxins on binding to insect sodium channels.
Delta-palutoxins from the spider Paracoelotes luctuosus (Araneae: Amaurobiidae) are 36-37 residue long peptides that show preference for insect sodium channels (NaChs) and modulate their function. Although they slow NaCh inactivation in a fashion similar to that of receptor site 3 modifiers, such as scorpion alpha-toxins, they actually bind with high affinity to the topologically distinct receptor site 4 of scorpion beta-toxins. To resolve this riddle, we scanned by Ala mutagenesis the surface of delta-PaluIT2, a delta-palutoxin variant with the highest affinity for insect NaChs, and compared it to the bioactive surface of a scorpion beta-toxin. We found three regions on the surface of delta-PaluIT2 important for activity: the first consists of Tyr-22 and Tyr-30 (aromatic), Ser-24 and Met-28 (polar), and Arg-8, Arg-26, Arg-32, and Arg-34 (basic) residues; the second is made of Trp-12; and the third is made of Asp-19, whose substitution by Ala uncoupled the binding from toxicity to lepidopteran larvae. Although spider delta-palutoxins and scorpion beta-toxins have developed from different ancestors, they show some commonality in their bioactive surfaces, which may explain their ability to compete for an identical receptor (site 4) on voltage-gated NaChs. Yet, their different mode of channel modulation provides a novel perspective about the structural relatedness of receptor sites 3 and 4, which until now have been considered topologically distinct.
Corzo
Gerardo
G
Suntory Institute for Bioorganic Research, Mishima-gun, Shimamoto-cho, Wakayamadai 1-1-1, Osaka 618-8503, Japan. corzo@ibt.unam.mx
Escoubas
Pierre
P
Villegas
Elba
E
Karbat
Izhar
I
Gordon
Dalia
D
Gurevitz
Michael
M
Nakajima
Terumi
T
Gilles
Nicolas
N
D000409:Alanine / Q000235:genetics; D000818:Animals; D001667:Binding, Competitive; D019476:Insect Proteins; D016297:Mutagenesis, Site-Directed; D009498:Neurotoxins / Q000378:metabolism / Q000633:toxicity*; D010526:Periplaneta / Q000187:drug effects / Q000378:metabolism; D011485:Protein Binding; D012604:Scorpion Venoms / Q000378:metabolism* / Q000633:toxicity*; D015222:Sodium Channels / Q000378:metabolism*; D013111:Spider Venoms / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity*; D018411:Spodoptera / Q000187:drug effects / Q000378:metabolism
C115530:Bj-xtrIT toxin; D019476:Insect Proteins; C065190:LqhalphaIT toxin; D009498:Neurotoxins; D012604:Scorpion Venoms; D015222:Sodium Channels; D013111:Spider Venoms; C500898:delta-palutoxin IT2, Paracoelotes lunctuosus; D000409:Alanine