Antimicrobial peptides in insects; structure and function

Antimicrobial peptides appear to be ubiquitous and multipotent components o f the innate immune defense arsenal used by both prokaryotic and eukaryotic organisms. During the past 15 years a multitude of these peptides have bee n isolated largely from insects. In spite of great differences in size, ami no acid composition and structure, most of the antimicrobial peptides from insects can be grouped into one of three categories, The largest category i n number contains peptides with intramolecular disulfide bonds forming hair pin-like beta-sheets or alpha-helical-beta-sheet mixed structures. The seco nd most important group is composed of peptides forming amphipathic alpha-h elices. The third group comprises peptides with an overrepresentation in pr oline and/or glycine residues. In general, the insect antimicrobial peptide s have a broad range of activity and are not cytotoxic. Despite a wealth of information on structural requirements for their antimicrobial activity. t he mode of action of these peptides is not yet fully understood. However, s ome data suggest the existence of two types of mode of action: 1. through peptide-lipid interaction or 2. through receptor-mediated recognition processes. This review presents the main results obtained during the last four years i n the field of antimicrobial peptides from insects with a special focus on the proline-rich and cysteine-rich peptides. (C) 1999 Elsevier Science Ltd. All rights reserved.