Major basic protein

Function

The protein encoded by this gene is the predominant constituent of the crystalline core of the eosinophil 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 and helmintho-toxin, and in immune hypersensitivity reactions. It is directly implicated in epithelial cell damage, exfoliation, and bronchospasm in allergic diseases.

PRG2 is a 117-residue protein that predominates in eosinophil granules. It is a potent enzyme against helminths and is toxic towards bacteria and mammalian cells in vitro. The eosinophil major basic protein also causes the release of histamine from mast cells and basophils, and activates neutrophils and alveolar macrophages.

Structure

Structurally the major basic protein (MBP) is similar to lectins (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 in the presence of calcium), MBP does not bind either calcium or any of the other carbohydrates that this family recognize.

Instead, MBP recognises heparan sulfate proteoglycans. Two crystallographic structures of MBP have been determined.

Interactions

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

References

References

1. "Entrez Gene: PRG2 proteoglycan 2, bone marrow (natural killer cell activator, eosinophil granule major basic protein)".
2. (July 2001). "Crystal structure of the eosinophil major basic protein at 1.8 A. An atypical lectin with a paradigm shift in specificity". J. Biol. Chem..
3. (November 2005). "Eosinophil-granule major basic protein, a C-type lectin, binds heparin". Biochemistry.
4. Overgaard, M T. (October 2000). "Expression of recombinant human pregnancy-associated plasma protein-A and identification of the proform of eosinophil major basic protein as its physiological inhibitor". J. Biol. Chem..
5. (January 2003). "Complex of pregnancy-associated plasma protein-A and the proform of eosinophil major basic protein. Disulfide structure and carbohydrate attachment". J. Biol. Chem..
6. Oxvig, C. (June 1993). "Circulating human pregnancy-associated plasma protein-A is disulfide-bridged to the proform of eosinophil major basic protein". J. Biol. Chem..