Docking and Simulation Study of Fusion Protein (Cry1Ac-Vip3aa) with Aminopeptidase N Receptor of <i>Helicoverpa armigera</i> (Hubner)

Helicoverpa armigera (Hubner), a major polyphagous pest, poses a significant threat to crop yield due to its resistance to chemical insecticides and transgenic crops expressing a single transgene from Bacillus thuringiensis (Bt). Gene pyramiding with multiple toxin genes or fusion proteins is a potential strategy to combat this resistance against this pest. This study analysed the Cry1Ac34-Vip3Aa44 fusion protein for its interactions with the aminopeptidase N (APN) receptor, a key Cry protein target through molecular docking and simulation (MDS) studies. Docking analyses with ClusPro 2.0 and molecular dynamics (MD) simulations (GROMACS 2021.1) evaluated three systems: Cry1Ac34 alone, Cry1Ac34-Vip3Aa44 with APN1, and Cry1Ac34 with APN1. The Cry1Ac34 toxic region strongly binds with APN1, forming a highly stable complex, while the Cry1Ac34-Vip3Aa44 fusion protein formed moderately stable complexes. Incorporating Vip3Aa44 domains increased residual fluctuations in the fusion-APN1 complex, consistent with the weaker interactions of Vip3A with APN1. Despite being slightly lower stable than Cry1Ac34, the relative stability of fusion protein (instability index of 34.82) offers its potential to combat resistance development in pest populations.