Structural foundation for the insect-selective activity of acylpolyamine toxins from spider Araneus ventricosus.

Spider venoms are insecticidal mixtures with diverse biological activities, and acylpolyamines are their small molecular active components. However, the mechanism for the insecticidal activity of acylpolyamines remains to be elucidated. Here, the structure and function of two acylpolyamine toxins, AVTX-622 and AVTX-636, from Araneus ventricosus were investigated. Nuclear magnetic resonance (NMR) analysis illustrated that the structure of two toxins was very similar, and compared to AVTX-636, AVTX-622 only missed a methylene group in the linker region between the polyamine head and tail. Both the two toxins did not inhibit on voltage-gated sodium channels in mammalian neuronal cells. Intriguingly, AVTX-622, but not AVTX-636, inhibited voltage-gated sodium channels in DUM neuronal cells of Periplaneta americana. Further animal test displayed that the paralyzing potency of AVTX-622 on insect was over ten times stronger than that of AVTX-636. These findings indicate that a single methylene deletion from AVTX-636 offered AVTX-622 the insect-selective voltage-gated sodium channel activity, which not only elucidated structure-function of the toxins, but also provided new clues for insect-selective insecticide design.