Pyrrhocoricin is a 20-residue long

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 an ...

of the firebug ''

Pyrrhocoris apterus The firebug, ''Pyrrhocoris apterus'', is a common insect of the family Pyrrhocoridae. Easily recognizable due to its striking red and black coloration, it may be confused with the similarly coloured though unrelated ''Corizus hyoscyami'' (cinna ...

''.

Structure and function

Pyrrhocoricin is primarily active against

Gram-negative bacteria Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...

. The peptide is proline-rich with proline-arginine repeats, as well a critical threonine residue, which is required for activity through ''O''-glycosylation. Like the antimicrobial peptides

drosocin Drosocin is a 19-residue long antimicrobial peptide (AMP) of flies first isolated in the fruit fly ''Drosophila melanogaster'', and later shown to be conserved throughout the genus ''Drosophila''. Drosocin is regulated by the NF-κB Imd signalli ...

and abaecin, pyrrhocoricin binds to the bacterial protein

DnaK The 70 kilodalton heat shock proteins (Hsp70s or DnaK) are a family of conserved ubiquitously expressed heat shock proteins. Proteins with similar structure exist in virtually all living organisms. Intracellularly localized Hsp70s are an importa ...

, inhibiting cell machinery and replication. Only the L-enantiomer of pyrrhocoricin is active against bacteria. The action of pyrrhocoricin-like peptides is potentiated by the presence of pore-forming peptides, which facilitates the entry of pyrrhocoricin-like peptides into the bacterial cell. Proline-rich peptides like Pyrrhocoricin can also bind to microbe

ribosomes Ribosomes ( ) are macromolecular machines, found within all cells, that perform biological protein synthesis (mRNA translation). Ribosomes link amino acids together in the order specified by the codons of messenger RNA (mRNA) molecules to f ...

, preventing

protein translation In molecular biology and genetics, translation is the process in which ribosomes in the cytoplasm or endoplasmic reticulum synthesize proteins after the process of transcription of DNA to RNA in the cell's nucleus. The entire process is ...

. In the absence of pore-forming peptides, pyrrhocoricin is taken into the bacteria by the action of bacterial uptake permeases.

References

{{Reflist Insect immunity Antimicrobial peptides