Glycine-rich antimicrobial peptides in basal insects: novel evolutionary insights from Archaeognatha and Zygentoma

A wide variety of glycine-rich antimicrobial peptides (AMPs) have been described in insects over the past few decades, where their role in the innate immune response against microbial infections has been well established. Despite their diversity, these AMPs display a shared molecular signature located in the C-terminal region of their precursors, which corresponds to the mature peptide region. To date, this heterogeneous AMP class has been mostly investigated in Holometabola, with only sporadic reports from other insect groups, hinting at a broader distribution. In this context, the study of Archaeognatha and Zygentoma, the two most basal orders of wingless insects, may offer key insights into the evolutionary origins of glycine-rich AMPs in insects. In this study, a detailed analysis of available omics data revealed three distinct types of Zygenotma/Archaeognatha glycine-rich AMPs (ZAgrAMPs), markedly different from those previously characterized in other insects. Whereas type I sequences were shared by both investigated insect orders, type II and type III AMPs were found exclusively in Archaeognatha. Intriguingly, structural predictions strongly suggest that ZAgrAMPs exhibit a high content of antiparallel β-sheets, likely forming β-barrel multimeric assemblies, potentially able to generate pores in microbial membranes, thereby explaining their antimicrobial activity.