Identification and Molecular Characterization of a Serine Protease Inhibitor Gene in the Khapra Beetle Trogoderma granarium

Insect serine protease inhibitors (ISPIs) are essential for regulating various protease-mediated activities and play crucial roles in metabolism, metamorphosis, reproduction, and immunity. As a member of the ISPIs, serpins are recognized as the most essential protease inhibitor family in higher eukaryotes, encompassing a diverse array of biological functions. They are involved in the Toll pathway, the prophenoloxidase cascade, development, immunity, and reproduction in all insects. In this study, a serpin from the khapra beetle, Trogoderma granarium (Everts) (Coleoptera: Dermestideae) was identified and characterized using both transcriptomic and bioinformatics methodologies. The BGISEQ-500 platform was used to construct a cDNA library from T. granarium, which led to the identification and characterization of a novel Serine Protease Inhibitor gene (TgSPI). Sequence analysis confirmed TgSPI's classification within the serine protease inhibitor (SPI) superfamily. It has conserved features, including a Reactive Center Loop (RCL) close to the C-terminal end, which is essential for protease inhibition. Phylogenetic analysis and 3D structure modeling of TgSPI were performed using MEGA6 software and the Phyre2 Protein Fold Recognition Server, respectively. The phylogenetic analysis positioned TgSPI within a cluster of coleopteran insect SPIs (ISPIs), supporting its evolutionary lineage. Predicted tertiary structure modeling of TgSPI revealed similarity to conserpin in the latent state. This study provides foundational information on the evolutionary patterns and structural-functional aspects of TgSPI in the khapra beetle and highlights probable role of TgSPI as a promising target for further genetic and functional studies aimed at sustainable pest control strategies.