Drosomycin is a 44-residue defensin-like peptide containing four disulfide bridges. These bridges stabilize a structure involving one α-helix and three β-sheets. Owing to these four disulfide bridges, drosomycin is resistant to degradation and the action of proteases.[1][11][12] The cysteine stabilized αβ motif of drosomycin is also found in Drosophiladefensin, and some plant defensins. Drosomycin has greater sequence similarity with these plant defensins (up to 40%), than with other insect defensins.[13] The structure was discovered in 1997 by Landon and his colleagues[14] The αβ motif of drosomycin is also found in a scorpion neurotoxin, and drosomycin potentiates the action of this neurotoxin on nerve excitation.[15]
At the nucleotide level, drosomycin is a 387 bp-long gene (Drs) which lies on Muller element 3L,[16] very near six other drosomycin-like (Drsl) genes. These various drosomycins are referred to as the drosomycin multigene family. However, only drosomycin itself is part of the systemic immune response, while the other genes are regulated in different fashions. The antimicrobial activity of these various drosomycin-like peptides also differs.[17] In 2015 Gao and Zhu[18] found that in some Drosophila species (D. takahashii) some of these genes have been duplicated and this Drosophila has 11 genes in the drosomycin multigene family in total.
It seems that drosomycin has about three major functions on fungi, the first is partial lysisofhyphae, the second is inhibition of spore germination (in higher concentrations of drosomycin), and the last is delaying of hypha growth, which leads to hyphae branching (at lower concentrations of drosomycin).[19] The exact mechanism of function to fungi still has to be clarified. In 2019, Hanson and colleagues[20] generated the first drosomycin mutant, finding that indeed flies lacking drosomycin were more susceptible to fungal infection.
^Asling B, Dushay MS, Hultmark D (April 1995). "Identification of early genes in the Drosophila immune response by PCR-based differential display: the Attacin A gene and the evolution of attacin-like proteins". Insect Biochemistry and Molecular Biology. 25 (4): 511–8. doi:10.1016/0965-1748(94)00091-C. PMID7742836.
^Fant F, Vranken W, Broekaert W, Borremans F (May 1998). "Determination of the three-dimensional solution structure of Raphanus sativus antifungal protein 1 by 1H NMR". Journal of Molecular Biology. 279 (1): 257–70. doi:10.1006/jmbi.1998.1767. PMID9636715.