in silico identification of cross affinity towards Cry1Ac pesticidal protein with receptor enzyme in Bos taurus and sequence, structure analysis of crystal proteins for stability

Abstract

Any novel protein introduced into the GM crops need to be evaluated for cross affinity on living organisms. Many researchers are currently focusing on the impact of Bacillus thuringiensis cotton on soil and microbial diversity by field experiments. In spite of this, in silico approach might be helpful to elucidate the impact of cry genes. The crystal a protein which was produced by Bt at the time of sporulation has been used as a biological pesticide to target the insectivorous pests like Cry1Ac for Helicoverpa armigera and Cry2Ab for Spodoptera sp. and Heliothis sp. Here, we present the comprehensive in silico analysis of Cry1Ac and Cry2Ab proteins with available in silico tools, databases and docking servers. Molecular docking of Cry1Ac with procarboxypeptidase from Helicoverpa armigera and Cry1Ac with Leucine aminopeptidase from Bos taurus has showed the 125(th) amino acid position to be the preference site of Cry1Ac protein. The structures were compared with each other and it showed 5% of similarity. The cross affinity of this toxin that have confirmed the earlier reports of ill effects of Bt cotton consumed by cattle.

Keywords: Bacillus thuringiensis; Cross affinity; Crystal protein; Docking; Persistence; Phylogenetic analysis.

Figure 1

Three dimensional structures of Cry1Ac and Cry 2Ab. A) The template used for the structure prediction of Cry1Ac was 1CIYA- Cry1A insecticidal toxin; B) The template used for the structure predicition of Cry2Ab proteins was 1I5P- Cry2Aa insecticidal crystal protein. The structure visualization and modeling was done using the Discovery Studio from Accelerys software. A Ramachandran plot, against a background of phi-psi probabilities was constructed. Black shaded portion indicate fully Allowed region. Dark grey shaded portion indicate additionally allowed region, light grey shaded portion indicate generously Allowed region. Black triangles indicate glycine residues, white triangles indicate proline residues, and small black squares indicate other residues.

Figure 2

Docking of Cry1Ac protein tertiary structure. A) Cry1Ac protein with crystal structure of procarboxypeptidase A (Helicoverpa armigera) indicated that 125th aminoacid position (TYR-Tyrosine) to be preference site of the Cry1Ac protein; B) Cry1Ac protein with crystal structure of Leucine aminopeptidase (Bos taurus) indicated that 125th aminoacid position (Leu-Leucine) to be preference site of the Cry1Ac protein. Red color dots indicates water molecules.