A Spider Toxin X enhances toxicity to insects by expression as a fusion protein with a plant lectin X

Exploitation of specific insecticidal toxins from spider species in recombinant fusion proteins has the potential to lead to new environmentally-benign approaches for crop protection. The spider-venom peptide Toxin X was selected as a candidate toxin for fusion proteins on the basis of its activity and specificty; it has been shown to be non-toxic to higher animals. Toxin X targets insect voltage-gated sodium channels, acting directly at sites within the central nervous system (CNS). It is extremely insecticidal when injected into a wide variety of insect pests like cabbage moth (Mamestra brassica, Lepidoptera) larvae, pea aphids (Acyrthosiphon pisum, Hemiptera) and house fly (Musca domestica, Diptera). Toxin X has limited oral toxicity because in general it cannot cross the insect gut epithelium to access its sites of action. However, lectin X, which is capable of being transported to the haemolymph of insects after oral ingestion, can act as a ‘‘carrier’’ to enhance the oral activity of Toxin X. Toxin X itself and a Toxin X/lectin X fusion protein were produced using the yeast Pichia pastoris as expression host.