Diversity in Host Defense Antimicrobial Peptides

Abstract

Host defense antimicrobial peptides are part of the innate immune system of organisms in multicellular eukaryotes. Following the identification of the first insect antimicrobial peptide, cecropin, in moths in 1980 (Eur J Biochem 106(1):7–16, 1980; Nature 292(5820):246–248, 1981) and the first amphibian peptide magainin in 1987 (Proc Natl Acad Sci USA 84(15):5449–5453, 1987), scientists have been exploring the diversity of animal antimicrobial peptides through examination of their sequences, structures and functions. The sequences of antimicrobial host defense peptides are surprisingly diverse as is the lack of commonalities between animals across phyla. Although peptides are classified into categories such as cathelicidins and defensins, the similarity between the active peptides within these categories can sometimes be difficult to find. This is because these peptides share function, structure, and mechanism within groups but often have very different sequences (Clin Microbiol Rev 19(3):491–511, 2006). That is, they have significant structural conservation often without significant sequence conservation. Sorensen and Borregaard (Comb Chem High Throughput Screen 8(3):273–280, 2005) beautifully described the diversity of host defense and antimicrobial peptides as “nature’s attempt at combinatorial chemistry” (Comb Chem High Throughput Screen 8(3):273–280, 2005). In this chapter, we will discuss the diversity of antibacterial peptides from insects and oysters to reptiles and humans. Questions that could be of interest for future research and seem to be currently unanswered are highlighted in boxes throughout the text.