Defensin

Defensins are small (30-35 residue) cysteinerich cationicproteinsfound in vertebratephagocytes(notably the azurophilgranulesof neutrophils) and active against bacteria, fungiand enveloped viruses. Most defensins function via penetrating the microbial's cell membraneby way of electrical attraction, and once embedded, forming a pore in the membrane which allows efflux.

The underlying genes responsible for defensin production are highly polymorphic. Some aspects are conserved, however; the hallmarks of a β-defensin are its small size, high density of cationic charge and six-cysteine-residue motif. Generally they are encoded by two-exon genes, where the first exon encodes for a hydrophobic leader sequence and the second for a peptide containing the cysteine motif.

There are three main (known) forms of defensins; α-defensins, β-defensins, and θ-defensins. α-defensins are expressed primarily in neutrophilsas well as macrophagesand the Paneth cellsof the intestines (where they help maintain the correct microbial balance). β-defensins are the most widely distributed, being secreted by leukocytesand epithelialcells of many kinds. For example, they can be found on the tongue, skin, cornea, salivary glands, kidneys, oesophagus, and respiratory tract. It is theorised that one of the causes of cystic fibrosisis inhibition of β-defensin activity on the epithelial surfaces of the lungs and trachaea due to higher salt content. θ-defensins are rare, and thus far have been found only in the leukocytes of the rhesus macaque.

In immature marsupials, due to the fact that their immune systemis underdeveloped at the time of birth, defensins play a major role in defense against pathogens. They are produced in the milk of the mother as well as by the young marsupial in question. It is also interesting to note that retrocyclin- a defensin created artificially by `fixing' a human psuedogene- is effective against HIV, though the mechanism by which it does this is unknown.

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It uses material from the http://en.wikipedia.org/wiki/Defensin Wikipedia article Defensin.