Drosomycin, an essential component of antifungal defence in Drosophila.

Drosomycin is an inducible antifungal peptide of 44 residues initially isolated from bacteria-challenged Drosophila melanogaster. The systemic expression of drosomycin is regulated by the Toll pathway present in fat body, whereas inducible local expression in the respiratory tract is controlled by the Immune Deficiency (IMD) pathway. Drosomycin belongs to the cysteine-stabilized alpha-helical and beta-sheet (CSalphabeta) superfamily and is composed of an alpha-helix and a three-stranded beta-sheet stabilized by four disulphide bridges. Drosomycin exhibits a narrow antimicrobial spectrum and is only active against some filamentous fungi. However, recent work using recombinant drosomycin expressed in Escherichia coli revealed its antiparasitic and anti-yeast activities. Two evolutionary epitopes (alpha- and gamma-patch) and the m-loop have been proposed as putative functional regions of drosomycin for interaction with fungi and parasites, respectively. Similarity in sequence, structure and biological activity suggests that drosomycin and some defensin molecules from plants and fungi could originate from a common ancestor.