Eosinophil major basic protein, often shortened to major basic protein (MBP; also called proteoglycan 2 (PRG2)) is encoded in humans by the ''PRG2''

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

Function

The protein encoded by this gene is the predominant constituent of the crystalline core of the

eosinophil Eosinophils, sometimes called eosinophiles or, less commonly, acidophils, are a variety of white blood cells and one of the immune system components responsible for combating multicellular parasites and certain infections in vertebrates. Along wi ...

granule. High levels of the proform of this protein are also present in placenta and pregnancy serum, where it exists as a complex with several other proteins including pregnancy-associated plasma protein A ( PAPPA), angiotensinogen ( AGT), and C3dg. This protein may be involved in antiparasitic defense mechanisms as a

cytotoxin Cytotoxicity is the quality of being toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium ...

and

helminth Parasitic worms, also known as helminths, are a polyphyletic group of large macroparasites; adults can generally be seen with the naked eye. Many are intestinal worms that are soil-transmitted and infect the gastrointestinal tract. Other par ...

o-toxin, and in immune hypersensitivity reactions. It is directly implicated in epithelial cell damage, exfoliation, and

bronchospasm Bronchospasm or a bronchial spasm is a sudden bronchoconstriction, constriction of the muscles in the walls of the bronchioles. It is caused by the release (degranulation) of substances from mast cells or basophils under the influence of anaphylat ...

in allergic diseases. PRG2 is a 117-residue protein that predominates in

granules. It is a potent enzyme against

helminths Parasitic worms, also known as helminths, are a polyphyletic group of large macroparasites; adults can generally be seen with the naked eye. Many are intestinal worms that are soil-transmitted and infect the gastrointestinal tract. Other par ...

and is toxic towards bacteria and mammalian cells ''in vitro''. The

major basic protein also causes the release of

histamine Histamine is an organic nitrogenous compound involved in local immune responses communication, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Discovered in 19 ...

from

mast cells A mast cell (also known as a mastocyte or a labrocyte) is a resident cell of connective tissue that contains many granules rich in histamine and heparin. Specifically, it is a type of granulocyte derived from the myeloid stem cell that is a ...

and

basophils Basophils are a type of white blood cell. Basophils are the least common type of granulocyte, representing about 0.5% to 1% of circulating white blood cells. They are the largest type of granulocyte. They are responsible for inflammatory reactio ...

, and activates

neutrophils Neutrophils are a type of phagocytic white blood cell and part of innate immunity. More specifically, they form the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. Their functions vary in different ...

and alveolar

macrophages Macrophages (; abbreviated MPhi, φ, MΦ or MP) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris and foreign substances, which do not have proteins that ...

Structure

Structurally the major basic protein (MBP) is similar to

lectins Lectins are carbohydrate-binding proteins that are highly specific for sugar groups that are part of other molecules, so cause agglutination of particular cells or precipitation of glycoconjugates and polysaccharides. Lectins have a role in r ...

(sugar-binding proteins), and has a fold similar to that seen in C-type lectins. However, unlike other C-type lectins (those that bind various

carbohydrates A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ma ...

in the presence of

calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...

), MBP does not bind either calcium or any of the other carbohydrates that this family recognize. Instead, MBP recognises

heparan sulfate Heparan sulfate (HS) is a linear polysaccharide found in all animal tissues. It occurs in a proteoglycan (HSPG, i.e. Heparan Sulfate ProteoGlycan) in which two or three HS chains are attached in close proximity to cell surface or extracellular ma ...

proteoglycans Proteoglycans are proteins that are heavily glycosylation, glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalent bond, covalently attached glycosaminoglycan (GAG) chain(s). The point of attachment is a ...

. Two crystallographic structures of MBP have been determined.; ;

Interactions

Major basic protein has been shown to interact with pregnancy-associated plasma protein A.

References

External links

* * {{Granule contents Human proteins

Function

Structure

Interactions

See also

References

Further reading

External links