Beta defensin
| Beta defensin | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| OPM superfamily | 54 | ||||||||
| OPM protein | 1ut3 | ||||||||
| |||||||||
Beta defensins are a family of vertebrate defensins. The beta defensins are antimicrobial peptides implicated in the resistance of epithelial surfaces to microbial colonization.
Defensins are 2-6 kDa, cationic, microbicidal peptides active against many Gram-negative and Gram-positive bacteria, fungi, and enveloped viruses,[1] 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. Every mammalian species explored thus far has beta-defensins. In cows, as many as 13 beta-defensins exist in neutrophils. However, in other species, beta-defensins are more often produced by epithelial cells lining various organs (e.g. the epidermis, bronchial tree and genitourinary tract).
Human, rabbit and guinea-pig beta-defensins, as well as human beta-defensin-2 (hBD2), induce the activation and degranulation of mast cells, resulting in the release of histamine and prostaglandin D2.[2]
Genes
β-defensins are coding for genes which impact the function of the
Initiation
Receptors such as
Function
β-defensins are cationic and can therefore interact with the
Defensins not only have the ability to strengthen the
Avian β-defensins
β-defensins are classified in three classes and avian β-defensins constitute for one of the classes.
Avian β-defensins are separated in avian
Avian heterophiles lack protective oxidative mechanisms, such as superoxide and myeloperoxidase, making non-oxidative mechanisms, such as lysosomes and cationic peptides, even more important.[9]
Evolution
β-defensins genes are found across the vertebrates, including mammals, reptiles, birds and fish.[10] The fact that alpha and theta defensins are absent in older vertebrates, like birds and fishes, indicates that defensins must have evolved from the same ancestral gene coding for β-defensins.[11] Indeed, these defensins of this superfamily are related to the 'big defensins' which are found in invertebrate animals, indicating even earlier origins.[10]
In 2001, it was thought that β-defensins were similar to the ancestral defensin from a comparison of sequences of β-defensins,
In addition to other antimicrobial defensins, there are related defensin-like proteins with have evolved other functions. These include toxins found in snakes (e.g. crotamine), bearded lizards and platypus.[14]
History
The first beta-defensin discovered was Tracheal Antimicrobial Peptide, found in the bovine airway in 1991.[15] The first human beta-defensin, HBD1, was discovered in 1995,[2] followed by the HBD2 in 1997.[16]
Human proteins containing this domain
; DEFB114; DEFB130; DEFB136; DEFB4; SPAG11A;See also
References
Further reading
- Liu L, Zhao C, Heng HH, Ganz T (August 1997). "The human beta-defensin-1 and alpha-defensins are encoded by adjacent genes: two peptide families with differing disulfide topology share a common ancestry". Genomics. 43 (3): 316–20. PMID 9268634.