Cationic Antimicrobial Peptides—The Defensins

ABSTRACT The term defensin relates different families of host defense peptides (HDPs) in vertebrates, invertebrates, plants, and molds that display structural similarities based on a cystine stabilized antiparallel β-sheet core, with an N-terminal α-helical stretch in many members. Despite structural and functional similarities, invertebrate/plant and vertebrate defensins belong to two distinct phylogenetic groups, and whether a unified relationship exists is controversial. Most defensins show a direct, salt- and medium-sensitive antimicrobial activity in vitro, with varying spectra, which requires interaction with the microbial membrane, although the mode of action differs markedly for defensins both within and from different families. A regulatory role in innate and adaptive immunity has also been observed for mammalian defensins.