Arthropod defensin

Arthropod defensins are a family of insect and scorpion cysteine-rich antibacterial peptides, primarily active against Gram-positive bacteria. All these peptides range in length from 38 to 51 amino acids. There are six conserved cysteines all involved in intrachain disulfide bonds. The role of these highly conserved cysteines is not known. Studies have shown that disulfide bonds are not required for antimicrobial activity. Mammalian defensins also do not require disulfide bonds to exhibit antimicrobial activity. Furthermore, it was also shown that the N-terminal helix region in arthropod or insect defensins is also not required for antimicrobial activity of these peptides.

A schematic representation of peptides from the arthropod defensin family is shown below.

+----------------------------+ | | xxCxxxxxxxxxxxxxxCxxxCxxxxxxxxxCxxxxxCxCxx | | | | +---|---------------+ | +-----------------+

'C': conserved cysteine involved in a disulfide bond.

Although low level sequence similarities have been reported between the arthropod defensins and mammalian defensins, the topological arrangement of the disulfide bonds as well as the tertiary structure are completely different in the two families.