Beta-defensin 126 (IPR020329)

Short name: Beta_defensin_126

Family relationships


Defensins are 2-6 kDa, cationic, microbicidal peptides active against many Gram-negative and Gram-positive bacteria, fungi, and enveloped viruses [PMID: 8528769], containing three pairs of intramolecular disulphide bonds. On the basis of their size and pattern of disulphide 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).

Defensins are produced constitutively and/or in response to microbial products or proinflammatory cytokines. Some defensins are also called corticostatins (CS) 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 synthesised as propeptides which may be relevant to this process.

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.

This entry includes Beta defensin-126 and its homologues. Beta defensin-126 coats the entire primate sperm surface and is a candidate for providing immune protection in the female reproductive tract. Beta defensin-126 also protects the entire primate sperm surface from immune recognition and the sialic acid moieties are responsible for the cloaking characteristic of this unique glycoprotein [PMID: 16079310]. The mouse homologue, Beta defensin-22, is synthesized in the murine corpora epididymides and coats mature sperm [PMID: 18787081].

Beta-Defensin has also been identified independently as ESP13.2 (Epididymal secretory protein 13.2), a small, secretory protein with a disulphide-stabilised core expressed specifically in epithelial cells lining the efferent ductules, initial segment, and cauda regions of the epididymis [PMID: 10491631].

GO terms

Biological Process

GO:0045087 innate immune response

Molecular Function

No terms assigned in this category.

Cellular Component

GO:0005576 extracellular region

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.