An evaluation of garlic lectin as an alternative carrier domain for insecticidal fusion proteins

The mannose-binding lectin GNA (snowdrop lectin) is used as a carrier domain in insecticidal fusion proteins which cross the insect gut after oral ingestion. A similar lectin from garlic bulb, ASAII, has been evaluated as an alternative carrier. Recombinant ASAII delivered orally to larvae of cabbage moth (Mamestra brassica; Lepidoptera) was subsequently detected in haemolymph, demonstrating transport. Fusion proteins comprising an insect neurotoxin, ButaIT (Buthus tamulus insecticidal toxin; red scorpion toxin) linked to the C-terminal region of ASAII or GNA were produced as recombinant proteins (GNA/ButaIT and ASA/ButaIT) by expression in Pichia pastoris. In both cases the C-terminal sequence of the lectin was truncated to avoid post-translational proteolysis. The GNA-containing fusion protein was toxic by injection to cabbage moth larvae (LD50 approximate to 250 mu g/g), and when fed had a negative effect on survival and growth. It also decreased the survival of cereal aphids (Sitobion avenae; Homoptera) from neonate to adult by > 70% when fed. In contrast, the ASA-ButaIT fusion protein was non-toxic to aphids, and had no effect on lepidopteran larvae, either when injected or when fed. However, intact ASA-ButaIT fusion protein was present in the haemolymph of cabbage moth larvae following ingestion, showing that transport of the fusion had occurred. The stabilities of GNA/ButaIT and ASA/ButaIT to proteolysis in vivo after injection or ingestion differed, and this may be a factor in determining insecticidal activities.