Insect Antimicrobial Peptides, a Mini Review

Abstract

Antimicrobial peptides (AMPs) are crucial effectors of the innate immune system. They provide the first line of defense against a variety of pathogens. AMPs display synergistic effects with conventional antibiotics, and thus present the potential for combined therapies. Insects are extremely resistant to bacterial infections. Insect AMPs are cationic and comprise less than 100 amino acids. These insect peptides exhibit an antimicrobial effect by disrupting the microbial membrane and do not easily allow microbes to develop drug resistance. Currently, membrane mechanisms underlying the antimicrobial effects of AMPs are proposed by different modes: the barrel-stave mode, toroidal-pore, carpet, and disordered toroidal-pore are the typical modes. Positive charge quantity, hydrophobic property and the secondary structure of the peptide are important for the antibacterial activity of AMPs. At present, several structural families of AMPs from insects are known (defensins, cecropins, drosocins, attacins, diptericins, ponericins, metchnikowins, and melittin), but new AMPs are frequently discovered. We reviewed the biological effects of the major insect AMPs. This review will provide further information that facilitates the study of insect AMPs and shed some light on novel microbicides.

Keywords: AMP; Structure-activity relationship; antimicrobial peptides; mechanism of action; modification.

Figure 1

Combined effects of antimicrobial peptides (AMPs) and antibiotics on bacteria. (A) AMPs can disrupt the bacterial membrane to cause the leakage of the cell content into the extracellular medium and kill the bacteria. The AMPs can facilitate more antibiotics to enter the cytoplasm of bacteria and finally interact with their target. However, the leakage of the antibiotics from the cytoplasm should not be ignored; (B) in bacterial cells, antibiotics are pumped out of the cells by the multidrug efflux pumps, which is how bacteria exert their resistance properties (adapted from [11]).

Figure 2

Amino-terminal sequence of attacins A–F. Their sequence difference can be observed from the highlighted residues.