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

Abstract

AbstractThe 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≈ 250 μg/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.