出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2013/12/17 16:11:09」(JST)
Beta-2-microglobulin | |||||||||||||
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PDB rendering based on 1a1m[1]. |
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Identifiers | |||||||||||||
Symbol | B2M | ||||||||||||
External IDs | OMIM: 109700 MGI: 88127 HomoloGene: 2987 ChEMBL: 1741302 GeneCards: B2M Gene | ||||||||||||
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RNA expression pattern | |||||||||||||
More reference expression data | |||||||||||||
Orthologs | |||||||||||||
Species | Human | Mouse | |||||||||||
Entrez | 567 | 12010 | |||||||||||
Ensembl | ENSG00000166710 | ENSMUSG00000060802 | |||||||||||
UniProt | P61769 | P01887 | |||||||||||
RefSeq (mRNA) | NM_004048 | NM_009735 | |||||||||||
RefSeq (protein) | NP_004039 | NP_033865 | |||||||||||
Location (UCSC) | Chr 15: 45 – 45.01 Mb |
Chr 2: 122.15 – 122.15 Mb |
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PubMed search | [1] | [2] | |||||||||||
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β2 microglobulin also known as B2M is a component of MHC class I molecules, which are present on all nucleated cells (excludes red blood cells).[2][3] In humans, the β2 microglobulin protein[4] is encoded by the B2M gene.[3][5]
β2 microglobulin lies lateral to the α3 chain on the cell surface. Unlike α3, β2 has no transmembrane region. Directly above β2 (i.e. away from the cell) lies the α1 chain, which itself is lateral to the α2.
β2 microglobulin associates not only with the alpha chain of MHC class I molecules, but also with class I-like molecules such as CD1 and Qa.
An additional function is association with the HFE protein, together regulating the expression of hepcidin in the liver which targets the iron transporter ferroportin on the cytoplasmic membrane of enterocytes and macrophages for degradation resulting in decreased iron uptake from food and iron release from recycled red blood cells respectively. Loss of this function causes iron excess and hemochromatosis.
In patients on long-term hemodialysis, it can aggregate into amyloid fibers that deposit in joint spaces, a disease known as dialysis-related amyloidosis.
Mice models deficient for the β2 microglobulin gene have been engineered. These mice demonstrate that β2 microglobulin is necessary for cell surface expression of MHC class I and stability of the peptide binding groove. In fact, in the absence of β2 microglobulin, very limited amounts of MHC class I (classical and non-classical) molecules can be detected on the surface. In the absence of MHC class I, CD8 T cells cannot develop. (CD8 T cells are a subset of T cells involved in the development of acquired immunity.) Low levels of β2 microglobulin can indicate non-progression of HIV.
Levels of beta-2 microglobulin can be elevated in multiple myeloma and lymphoma, though in these cases primary amyloidosis (amyloid light chain) and secondary amyloidosis (amyloid associated protein) are more common. The normal value of beta-2 microglobulin is <0.2 mg/dL.[6] However, with respect to multiple myeloma, the levels of beta2-microglobulin may also be at the other end of the spectrum. Diagnostic testing for multiple myeloma includes obtaining the beta2-microglobulin level, for this level is an important prognostic indicator. A patient with a level <0.004 g/L is expected to have a median survival of 43 months, while one with a level >0.004 g/L has a median survival of only 12 months.[7]
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関連記事 | 「beta」「be」 |
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