β ₂ -microglobulin

β 2 -microglobulin
	Schematic representation of the MHC I
	Existing structural data: see UniProt
Properties of human protein
Mass / length primary structure	99 amino acids
Identifier
Gene name	B2M
External IDs	OMIM : 109700 ; UniProt : P61769 ;
Occurrence
Homology family	B2M
Parent taxon	Chordates

β ₂ -microglobulin ( β ₂ M ) is the smaller soluble protein subunit of the main histocompatibility complex (MHC) class I. The MHC class I protein complex is found in vertebrates on the surface of almost all nucleated cells and is used for antigen presentation . Mutations in B2M - gene can destabilize the MHC and hereditary to a (rare) Hypoproteinemia lead.

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, β ₂ -microglobulin is neither membrane-anchored nor polymorphic . It only binds to the α subunit. In the human genome, the gene coding for β ₂ -microglobulin is located on chromosome 15 , in contrast to the other MHC genes located on chromosome 6 .

Clinical significance

In its free form, β ₂ -microglobulin tends to aggregate into long protein threads (β- fibrils ), which are then deposited as amyloids in the spaces between cells. This process can lead to hemodialysis-associated amyloidosis (also: AB amyloidosis ), especially in dialysis patients . Since the fibrils are resistant to the body's own defense mechanisms such as phagocytosis by immune cells, they cannot simply be removed. The amyloid deposits destroy the structure of the organs in the long term and thus lead to functional disorders. There is evidence that the deposits also have a direct toxic effect on cells.