Drosomycin is an antifungal

peptide Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Da or more are called proteins. Chains of fewer than twenty am ...

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Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (an insect of the Order (biology), order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the "vinegar fly", "pomace fly" ...

'' and was the first antifungal peptide isolated from

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

s. Drosomycin is induced by infection by the Toll signalling pathway, while expression in surface epithelia like the respiratory tract is instead controlled by the immune deficiency pathway (Imd). This means that drosomycin, alongside other antimicrobial peptides (AMPs) such as cecropins, diptericin, drosocin, metchnikowin and attacin, serves as a first line defence upon septic injury. However drosomycin is also expressed constitutively to a lesser extent in different tissues and throughout development.

Structure

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. The cysteine stabilized αβ motif of drosomycin is also found in ''Drosophila''

defensin Defensins are small cysteine-rich cationic proteins across cellular life, including vertebrate and invertebrate animals, plants, and fungi. They are host defense peptides, with members displaying either direct Antimicrobial, antimicrobial activit ...

, and some plant

s. Drosomycin has greater sequence similarity with these plant defensins (up to 40%), than with other insect defensins. The structure was discovered in 1997 by Landon and his colleagues The αβ motif of drosomycin is also found in a scorpion neurotoxin, and drosomycin potentiates the action of this neurotoxin on nerve excitation.

Drosomycin multigene family

At the nucleotide level, drosomycin is a 387 bp-long gene (''Drs'') which lies on Muller element 3L, 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. In 2015 Gao and Zhu 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.

Function

It seems that drosomycin has about three major functions on fungi, the first is partial lysis of hyphae, 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). The exact mechanism of function to fungi still has to be clarified. In 2019, Hanson and colleagues{{cite journal , vauthors = Hanson MA, Dostálová A, Ceroni C, Poidevin M, Kondo S, Lemaitre B , title = Synergy and remarkable specificity of antimicrobial peptides in vivo using a systematic knockout approach , journal = eLife , volume = 8 , date = February 2019 , pmid = 30803481 , pmc = 6398976 , doi = 10.7554/eLife.44341 , doi-access = free generated the first drosomycin mutant, finding that indeed flies lacking drosomycin were more susceptible to fungal infection.

References

Peptides Antifungals Defensins