Defensin

Defensin is a family of microbicidal and cytotoxic peptides that are active against many Gram-negative and Gram-positive bacteria, fungi, and enveloped viruses. They are produced and stored in the granules of neutrophils and paneth cells, which are located in the crypts of Lieberkühn in the small intestine.

Structure

Defensins are small cysteine-rich cationic proteins found in both vertebrates and invertebrates. They are typically composed of 18-45 amino acids, including six to eight conserved cysteine residues. These peptides have a triple-stranded beta-sheet structure stabilized by three intramolecular disulfide bonds.

Function

Defensins play a crucial role in the immune system's function against bacterial, fungal, and viral infections. They are able to kill or inhibit the growth of these pathogens by permeabilizing their cell membranes. Defensins also enhance the phagocytosis of bacteria and the production of cytokines, and they influence the migration of leukocytes to the site of infection.

Types

There are three main types of defensins in mammals: alpha-defensins, beta-defensins, and theta-defensins. Alpha-defensins are found in humans, rabbits, and rats, while beta-defensins are found in most mammals. Theta-defensins are only found in Old World monkeys and orangutans.

Clinical significance

Defensins have been implicated in a number of medical conditions, including inflammatory bowel disease, cystic fibrosis, and chronic obstructive pulmonary disease. They may also play a role in the immune response to HIV.

See also

• Antimicrobial peptides
• Innate immune system
• Host defense peptide

References

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