Bacillus thuringiensis toxin, Cry1C interacts with 128HLHFHLP134 region of aminopeptidase N of agricultural pest, Spodoptera litura

• In silico docking and biopanning identified a putative binding region of Cry1C 128HLHFHLP134 to APN of Spodoptera litura.
• Synthetic peptides homologous to domain II loop 2 and 3 of Cry1C competed Cry1C-APN binding.
• Alanines substitution of H128, H130, H132 and P134 affect the toxicity of Cry1C toxin to APN receptor of S. litura.

We modeled Cry1C toxin and its Aminopeptidase-N receptor and in silico docking analysis was performed. Further, we utilized biopanning against Cry1C followed by blocking assays and mutagenesis analysis to identify the binding epitope of SlAPN. We have identified a putative SlAPN binding region, APN-CRY (128HLHFHLP134). A derivative of SlAPN carrying the 128HLHFHLP134 region termed as binding region of APN (BR-APN) was cloned and its involvement in Cry1C binding and toxicity was checked. Cry1C-BR-APN binding was competed by synthetic peptides homologous to loop2 and loop3 of domain II but not by that of loopα. Additionally, alanines substitution of residues H128, H130, H132 and P134 affect the binding efficiency of receptor to Cry1C toxin (upto 4-fold lower affinity).These residues are also implicated in Cry1C toxicity as shown by the reduced ability to affect the mortality of Cry1C on S. litura larvae when toxin was preincubated with a fragment of the receptor.