Insects make up the largest and most diverse group of organisms on earth with estimated numbers of around 4,000,000 species to exist in total. Their immune system has evolved a complex arrangement of constitutive and inducible antimicrobial peptides (AMP) that are used to defend against invading microorganisms or facilitate a symbiotic lifestyle with a variety of microbes including bacteria and fungi. Several insect AMPs were found to exhibit notable activity against various human pathogens and thus they are considered as promising candidates for novel antibiotic drug development.

In our current work we aim to provide a global map of insect antimicrobial peptide distribution and to identify novel bioactive peptide templates. Particular focus is on the class of defensin-type peptides. Such peptides exhibit a well-defined structure consisting of a complex arrangement of α-helixes and β-sheets that are stabilized by three intramolecular disulfide-bonds. Together with a range of reported activities they represent ideal templates for structure-activity studies and peptide engineering (1).

Using a thorough in silico mining approach we analysed >120 insect species across all insect orders and were able to identify >320 defensin-type insect peptides. Our analyses provide a first large-scale overview of the distribution of insect AMPs and highlight their sequence diversity. Interestingly, we show the presence or absence of different defensin-type peptides to be restricted to individual species and orders, thus redefining their phylogenetic distribution.

This work not only expands our knowledge on insect defensin-type peptides, but also allows speculations regarding the role of individual defensin peptides in insect ecology. Analysis and correlation of peptide distribution and associated microbial environments may identify novel peptide templates for antimicrobial drug development against human pathogens.