Construction, Expression, and Identification of Double Light Chain (VL-VL) Antibody from a Unique Bt Cry1-Specific Monoclonal Antibody

Synergism of Cry1 Toxins by a Fusion Protein Derived from a Cadherin Fragment and an Antibody Peptide

Synergistic factors can enhance the toxicity of Bt toxins and delay the development of Bt resistance. Previous research has demonstrated that a Helicoverpa armigera cadherin fragment (HaCad-TBR) increased the toxicity of Cry1Ac in Plutella xylostella larvae but did not have a synergistic effect on Cry1B, Cry1C, and Cry1F toxins. In this study, a fusion protein (HaCad-TBR-2D3 VL) derived from HaCad-TBR and a Bt Cry1-specific antibody peptide was expressed in Escherichia coli. The HaCad-TBR-2D3 VL enhanced Cry1Ac toxicity more efficiently in insects and Sf9 cells than HaCad-TBR and also significantly increased the toxicity of Cry1B, Cry1C, and Cry1F toxins in insects. Further investigation indicated that the improved stability in insect midguts and higher binding capacity with Bt toxins contributed to the enhanced synergism of HaCad-TBR-2D3 VL over HaCad-TBR. This study suggested that Bt antibody fragments can potentially broaden the synergistic range of Bt receptor fragments, providing a theoretical foundation for developing broad-spectrum synergists for other biopesticides.

Docking-based generation of antibodies mimicking Cry1A/1B protein binding sites as potential insecticidal agents against diamondback moth (Plutella xylostella)

BACKGROUND

Broad use of insecticidal Cry proteins from Bacillus thuringiensis in biopesticides and transgenic crops has resulted in cases of practical field resistance, highlighting the need for novel approaches to insect control. Previously we described an anti-Cry1Ab idiotypic-antibody (B12-scFv) displaying toxicity against rice leafroller (Cnaphalocrocis medinalis) larvae, supporting the potential of antibodies for pest control. The goal of the present study was to generate insecticidal antibodies against diamondback moth (Plutella xylostella) larvae.

RESULTS

Four genetically engineered antibodies (GEAbs) were designed in silico from B12-scFv using three-dimensional (3D) structure and docking predictions to alkaline phosphatase (ALP) as a Cry1Ac receptor in P. xylostella. Among these GEAbs, the GEAb-dV_L antibody consisting of two light chains had overlapping binding sites with Cry1A and Cry1B proteins and displayed high binding affinity to P. xylostella midgut brush border membrane (BBM) proteins. Proteins in BBM identified by pull-down assays as binding to GEAb-dV_L included an ABC transporter and V-ATPase subunit A protein. Despite lacking the α-helical structures in Cry1A that are responsible for pore formation, ingestion of GEAb-dV_L disrupted the P. xylostella larval midgut epithelium and resulted in toxicity. Apoptotic genes were activated in gut cells upon treatment with GEAb-dV_L .

CONCLUSION

This study describes the first insecticidal GEAb targeting P. xylostella by mimicking Cry proteins. Data support that GEAb-dV_L toxicity is associated to activation of intracellular cell death pathways, in contrast to pore-formation associated toxicity of Cry proteins. This work provides a foundation for the design of novel insecticidal antibodies for insect control. © 2021 Society of Chemical Industry.