Bombyx mori transferrin: genomic structure, expression and antimicrobial activity of recombinant protein.

Transferrin (Tf) is a multifunctional, iron binding protein found in both vertebrates and invertebrates. Although transferrin has been suggested to play a role in innate immunity, its immunological function during infection has not been characterized. In this study, we identified and characterized Bombyx mori transferrin (BmTf). The promoter region of BmTf has numerous putative NF-kappaB binding sites, suggesting its possible function in innate immunity. Analysis of BmTf gene expression shows that it is highly inducible in response to a wide variety of pathogens including bacteria, fungus, and viruses. Recombinant BmTf protein produced in a baculovirus system exhibits iron binding capacity and antibacterial activity against various Gram-positive and -negative bacteria. Taken together, our results indicate that BmTf is an inducible immune effector molecule that may play an important role in pathogen clearance of insect innate immunity.