Diptericins are found throughout Diptera, but are most extensively characterized in Drosophilafruit flies. The mature structures of diptericins are unknown, though previous efforts to synthesize Diptericin have suggested Diptericin in Protophormia terraenovae is one linear peptide. Yet Drosophila melanogaster's Diptericin B peptide is likely cleaved into two separate peptides. Synthesis of Diptericin in vitro found activity of the full-length peptide, but independently synthesizing the two peptides and mixing them does not recapitulate Diptericin activity. Diptericin A activity is strongly tied to residues in the glycine-rich domain.
A polymorphism at a single residue in the diptericin glycine-rich domain drastically affects its activity against the Gram-negative bacteriumProvidencia rettgeri. Flies with a Diptericin A gene encoding a serine allele survive infection significantly more than flies with an arginine allele. It is unclear how frequently such polymorphisms may dictate host-pathogen interactions, but there is evidence of widespread balancing selection that diptericin is not the only AMP with such polymorphisms. This close association between diptericin and P. rettgeri is further supported by genetic approaches that show that diptericin is the only antimicrobial peptide of the Drosophilaimmune response that affects resistance to P. rettgeri. The fruit fly Diptericin gene "Diptericin B" has a unique structure that has been derived independently in both Tephritidae and Drosophila fruit flies. This represents convergent evolution of an antimicrobial peptide towards a common structure in two separate fruit-feeding lineages. More surprisingly, sub-lineages of both Tephritidae and Drosophila that have specialized on non-fruit food sources have subsequently lost Diptericin B. In the mushroom-feeding fruit flies Drosophila guttifera and Drosophila testacea, this loss appears to have happened independently, as the mutations in these species' Diptericin B genes are different. This repeated loss of Diptericin B in fruit flies that have diverged to feed on non-fruit foods suggests Diptericin B is attuned to a fruit-feeding lifestyle, but unimportant and possibly even deleterious in non-fruit ecologies. These observations are part of a growing body of evidence that antimicrobial peptides can have intimate associations with microbes, and perhaps host ecology, in contrast to the previous philosophy that these peptides act in generalist and redundant fashions.
Functions beyond antimicrobial activity
Diptericins can also have properties that reduce oxidative damage during the immune response.
Suppression of the diptericin B and attacin C genes in Drosophila leads to increased Sindbis virus growth.
Overexpression of diptericin and other antimicrobial peptides in the brains of flies leads to neurodegeneration.
The Drosophila'' diptericin B gene is required for memory formation.
