Isolation, synthesis and pharmacological characterization of δ-palutoxins IT, novel insecticidal toxins from the spider Paracoelotes luctuosus (Amaurobiidae)

Abstract

Four novel insecticidal toxins were isolated from the venom of the spider Paracoelotes luctuosus (Araneae: Amaurobiidae) and named δ-palutoxins IT1 to IT4. The four toxins are homologous 36-37 amino acid peptides reticulated by four disulfide bridges and three have amidated C-terminal residues. The δ-palutoxins are highly homologous with the previously described μ-agatoxins and curtatoxins (77-97%). The four peptides demonstrated significant toxicity against larvae of the crop pest Spodoptera litura (Lepidoptera: Noctuidae) in a microinjection bioassay, with LD50 values in the 9-50 μg per g of insect range. This level of toxicity is equivalent to that of several of the most active scorpion toxins used in the development of recombinant baculoviruses, and the δ-palutoxins appear to be insect specific. Electrophysiological experiments demonstrated that δ-palutoxin IT1, the most active toxin acts by affecting insect sodium channel inactivation, resulting in the appearance of a late-maintained sodium current, in a similar fashion to insecticidal scorpion α and α-like toxins and is thus likely to bind to channel receptor site 3. However, α-palutoxin IT1 was distinguished by its lack of effect on peak sodium conductance, on the early phase of sodium current inactivation and the absence of a shift in the activation voltage of the sodium channels. δ-Palutoxins are thus proposed as new insecticidal toxins related to the α and α-like scorpion toxins. They will be useful both in the development of recombinant baculoviruses in agrochemical applications and also as molecular probes for the investigation of molecular mechanisms of insect selectivity and structure and function of sodium channels.