LAUSR

Simple Summary In the honeybee Apis mellifera, apidermin 2 (APD 2) is known as a cuticular protein. However, the antimicrobial properties of A. mellifera APD 2 (AmAPD 2) have not been characterized. Herein, we provide the first demonstration that AmAPD 2 exhibits antibacterial and antifungal activities. We found that AmAPD 2 induced structural damage by binding to bacterial and fungal cell walls, indicating that AmAPD 2 has the antimicrobial action of an antimicrobial peptide. Our findings demonstrate a novel role of AmAPD 2 as an antimicrobial agent in honeybees. Abstract Apidermins (APDs) are known as structural cuticular proteins in insects, but their additional roles are poorly understood. In this study, we characterized the honeybee, Apis mellifera, APD 2 (AmAPD 2), which displays activity suggesting antimicrobial properties. In A. mellifera worker bees, the AmAPD 2 gene is transcribed in the epidermis, hypopharyngeal glands, and fat body, and induced upon microbial ingestion. Particularly in the epidermis of A. mellifera worker bees, the AmAPD 2 gene showed high expression and responded strongly to microbial challenge. Using a recombinant AmAPD 2 peptide, which was produced in baculovirus-infected insect cells, we showed that AmAPD 2 is heat-stable and binds to live bacteria and fungi as well as carbohydrates of microbial cell wall molecules. This binding action ultimately induced structural damage to microbial cell walls, which resulted in microbicidal activity. These findings demonstrate the antimicrobial role of AmAPD 2 in honeybees.