Biosynthesis of peptide antibiotics and innate immunity

Antimicrobial peptides (AMPs) are unique multifunctional molecules that play a substantial role in keeping the innate defense system active for all species belonging to plants, amphibians, mammals, and insects. These peptides are proven for their efficacy against many clinically significant bacteria, fungi, protozoans, and many viruses. AMPs are amphipathic and can be ribosomally synthesized (e.g., polymyxin B, gramicidin S, bacitracin) or nonribosomally synthesized (e.g., β-defensin, magainin, and thionin). Bacteria and fungi utilize an enzyme complex known as nonribosomal peptide synthetases (NRPS) to generate broad, structural, and physically active peptide molecules. Genes encoding these peptides are found among different cell types throughout the body, including different macrophages, polymorphonuclear leukocytes, and mucosal epithelial cells, indicating their prominent role in the innate defense of our immune system. This chapter describes the roles of AMPs in innate host defenses, as well as their expression in both eukaryotic and prokaryotic systems.