Beta-2 microglobulin
- OMIM: 109700
- UniProt: P61769
β2 -microglobulin ( ß2M ) is the smaller soluble protein subunit of the major histocompatibility complex ( MHC) class I. The MHC class I protein complex found in vertebrates on the surface of nearly all nucleated cells and is used for antigen presentation. Mutations in the B2M gene can destabilize the MHC and lead to a ( rare ) hereditary hypoproteinemia.
Structure and genetics
The human protein consists of 99 amino acids with a molecular mass of 11,731 Da. In contrast to the larger α subunit of the MHC class I complex, the β2 -microglobulin is not yet membranverankert polymorphic. It binds exclusively to the α - subunit. In the human genome which codes for β2 -microglobulin gene is located on chromosome 15, in contrast to other localized on chromosome 6 MHC genes.
Clinical Significance
β2 -microglobulin in free form tends to aggregate into long protein strands ( β fibrils ), which then deposited as amyloid in intercellular spaces. This process may, in particular in patients on dialysis to hemodialysis -associated amyloidosis (also: AB- amyloidosis ) cause. Since the fibrils to the body's own defense mechanisms such as phagocytosis by immune cells are resistant, they can not be easily removed. The amyloid deposits destroy the long-term structure of the organs and lead to malfunction. There is evidence that the deposits also exert a direct toxic effect on cells.
β2 -microglobulin as a biomarker
The plasma concentration of β2 -microglobulin is an important biomarker in laboratory medicine. The plasma concentration of β2 -microglobulin is used as a tumor marker for lymphoma, multiple myeloma, leukemia, pancreatic cancer and hepatocellular carcinoma. β2 -microglobulin can also be increased by diseases with increased cell turnover (infections, autoimmune diseases ), hepatitis, liver cirrhosis, AIDS. β2 - microglobulin, also plays a role in the determination of renal function. However, the determination of β -2 -microglobulin for the analysis of proteinuria due to its instability at low pH values is not more common.