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 b-sheet core,
with an N-terminal a-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.
