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Alpha defensin
From Wikipedia, the free encyclopedia
Alpha defensins are a family of mammalian defensin peptides of the alpha subfamily. They are also known as cryptdins and are produced within the small bowel. Cryptdin is a portmanteau of crypt and defensin.
Mammalian defensin | |||||||||
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![]() Structure of defensin HNP-3.[1] | |||||||||
Identifiers | |||||||||
Symbol | Defensin_1 | ||||||||
Pfam | PF00323 | ||||||||
InterPro | IPR006081 | ||||||||
PROSITE | PDOC00242 | ||||||||
SCOP2 | 1dfn / SCOPe / SUPFAM | ||||||||
TCDB | 1.C.19 | ||||||||
OPM superfamily | 54 | ||||||||
OPM protein | 1tv0 | ||||||||
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Defensins are 2-6 kDa, cationic, antimicrobial peptides active against many Gram-negative and Gram-positive bacteria, fungi, and enveloped viruses,[2] containing three pairs of intramolecular disulfide bonds. On the basis of their size and pattern of disulfide bonding, mammalian defensins are classified into alpha, beta and theta categories. Alpha-defensins, which have been identified in humans, monkeys and several rodent species, are particularly abundant in neutrophils, certain macrophage populations and Paneth cells of the small intestine.
Defensins are produced constitutively and/or in response to microbial products or proinflammatory cytokines. Some defensins are also called corticostatins because they inhibit corticotropin-stimulated corticosteroid production. The mechanism(s) by which microorganisms are killed and/or inactivated by defensins is not understood completely. However, it is generally believed that killing is a consequence of disruption of the microbial membrane. The polar topology of defensins, with spatially separated charged and hydrophobic regions, allows them to insert themselves into the phospholipid membranes so that their hydrophobic regions are buried within the lipid membrane interior and their charged (mostly cationic) regions interact with anionic phospholipid head groups and water. Subsequently, some defensins can aggregate to form 'channel-like' pores; others might bind to and cover the microbial membrane in a 'carpet-like' manner. The net outcome is the disruption of membrane integrity and function, which ultimately leads to the lysis of microorganisms. Some defensins are synthesized as propeptides which may be relevant to this process. Alpha defensins of the mouse bowel were historically called cryptdins when first discovered.