Diptericin is a 9 kDa

antimicrobial peptide Antimicrobial peptides (AMPs), also called host defence peptides (HDPs) are part of the innate immune response found among all classes of life. Fundamental differences exist between prokaryotic and eukaryotic cells that may represent targets for ...

(AMP) of flies first isolated from the blowfly '' Phormia terranova''. It is primarily active against

Gram-negative bacteria Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the Crystal violet, crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelo ...

, disrupting bacterial membrane integrity. The structure of this protein includes a

proline Proline (symbol Pro or P) is an organic acid classed as a proteinogenic amino acid (used in the biosynthesis of proteins), although it does not contain the amino group but is rather a secondary amine. The secondary amine nitrogen is in the p ...

-rich domain with similarities to the AMPs drosocin, pyrrhocoricin, and abaecin, and a glycine-rich domain with similarity to

attacin Attacin is a glycine-rich protein of about 20 kDa belonging to the group of antimicrobial peptides (AMP). It is active against Gram-negative bacteria. Attacin was first discovered in ''Hyalophora cecropia ''Hyalophora cecropia'', the cecropia m ...

. Diptericin is an iconic readout of immune system activity in flies, used ubiquitously in studies of ''

Drosophila ''Drosophila'' (), from Ancient Greek δρόσος (''drósos''), meaning "dew", and φίλος (''phílos''), meaning "loving", is a genus of fly, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or p ...

'' immunity. Diptericin is named after the insect order

Diptera Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advance ...

Structure and function

Diptericins are found throughout Diptera, but are most extensively characterized in ''

'' fruit 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.

Diptericin as a model for understanding the specificity of host-pathogen interactions

A polymorphism at a single residue in the diptericin glycine-rich domain drastically affects its activity against the Gram-negative bacterium '' Providencia 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 Balancing selection refers to a number of selective processes by which multiple alleles (different versions of a gene) are actively maintained in the gene pool of a population at frequencies larger than expected from genetic drift alone. Balancing ...

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 ''Drosophila'' immune 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 The Tephritidae are one of two fly families referred to as fruit flies, the other family being the Drosophilidae. The family Tephritidae does not include the biological model organisms of the genus '' Drosophila'' (in the family Drosophilidae ...

and ''

'' fruit flies. This represents

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...

of an

towards a common structure in two separate fruit-feeding lineages. This convergent evolution is driven by presence of ''

Acetobacter ''Acetobacter'' is a genus of acetic acid bacteria. Acetic acid bacteria are characterized by the ability to convert ethanol to acetic acid in the presence of oxygen. Of these, the genus ''Acetobacter'' is distinguished by the ability to oxidiz ...

'' bacteria in fruit-feeding ecologies. Absence of ''Acetobacter'' in other ecologies has led to subsequent loss of Diptericin B. Diptericin B loss is also convergent among lineages feeding on mushrooms or plants, including the mushroom-feeding fruit flies '' Leucophenga varia'', '' Drosophila guttifera'' and '' Drosophila testacea'', and plant-feeding '' Scaptomyza'' flies. These observations are part of a growing body of evidence that antimicrobial peptides can have intimate associations with microbes, and perhaps host

ecology Ecology () is the natural science of the relationships among living organisms and their Natural environment, environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosystem, and biosphere lev ...

, 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.

References

{{Reflist Drosophila Insect immunity Antimicrobial peptides