CD79A
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Cluster of differentiation CD79A also known as B-cell antigen receptor complex-associated protein alpha chain and MB-1 membrane glycoprotein, is a protein that in humans is encoded by the CD79A gene.[5]
The CD79a protein together with the related
It is associated with
Gene
The mouse CD79A gene, then called mb-1, was cloned in the late 1980s,[8] followed by the discovery of human CD79A in the early 1990s.[9][10] It is a short gene, 4.3 kb in length, with 5 exons encoding for 2 splice variants resulting in 2 isoforms.[5]
CD79A is conserved and abundant among ray-finned fish (actinopterygii) but not in the evolutionarily more ancient chondrichthyes such as shark.[11] The occurrence of CD79A thus coincides with the evolution of B cell receptors with greater diversity generated by recombination of multiple V, D, and J elements in bony fish contrasting the single V, D and J elements found in shark.[12]
Structure
CD79a is a membrane protein with an extracellular immunoglobulin domain, a single span transmembrane region and a short cytoplasmic domain.[5] The cytoplasmic domain contains multiple phosphorylation sites including a conserved dual phosphotyrosine binding motif, termed immunotyrosine-based activation motif (ITAM).[13][14] The larger CD79a isoform contains an insert in position 88-127 of human CD79a resulting in a complete immunoglobulin domain, whereas the smaller isoform has only a truncated Ig-like domain.[5] CD79a has several cysteine residues, one of which forms covalent bonds with CD79b.[15]
Function
CD79a plays multiple and diverse roles in B cell development and function. The CD79a/b heterodimer associates non-covalently with the immunoglobulin heavy chain through its transmembrane region, thus forming the BCR along with the immunoglobulin light chain and the pre-BCR when associated with the surrogate light chain in developing B cells. Association of the CD79a/b heterodimer with the immunoglobulin heavy chain is required for surface expression of the BCR and BCR induced calcium flux and protein tyrosine phosphorylation.[16] Genetic deletion of the transmembrane exon of CD79A results in loss of CD79a protein and a complete block of B cell development at the pro to pre B cell transition.[17] Similarly, humans with homozygous splice variants in CD79A predicted to result in loss of the transmembrane region and a truncated or absent protein display agammaglobulinemia and no peripheral B cells.[7][18][19]
The CD79a ITAM tyrosines (human CD79a Tyr188 and Tyr199, mouse CD79a Tyr182 and Tyr193) phosphorylated in response to BCR crosslinking, are critical for binding of Src-homology 2 domain-containing kinases such as spleen tyrosine kinase (Syk) and signal transduction by CD79a.[20][21] In vivo, the CD79a ITAM tyrosines synergize with the CD79b ITAM tyrosines to mediate the transition from the pro to the pre B cell stage as suggested by the analysis of mice with targeted mutations of the CD79a and CD79b ITAM.[22][23] Loss of only one of the two functional CD79a/b ITAMs resulted in impaired B cell development but B cell functions such as the T cell independent type II response and BCR mediated calcium flux in the available B cells were intact. However, the presence of both the CD79a and CD79b ITAM tyrosines were required for normal T cell dependent antibody responses.[22][24] The CD79a cytoplasmic domain further contains a non-ITAM tyrosine distal of the CD79a ITAM (human CD79a Tyr210, mouse CD79a Tyr204) that can bind BLNK and Nck once phosphorylated,[25][26][27] and is critical for BCR mediated B cell proliferation and B1 cell development.[28] CD79a ITAM tyrosine phosphorylation and signaling is negatively regulated by serine and threonine residues in direct proximity of the ITAM (human CD79a Ser197, Ser203, Thr209; mouse CD79a Ser191, Ser197, Thr203),[29][30] and play a role in limiting formation of bone marrow plasma cells secreting IgG2a and IgG2b.[23]
Diagnostic relevance
The CD79a protein is present on the surface of B-cells throughout their life cycle, and is absent on all other healthy cells, making it a highly reliable marker for B-cells in
See also
References
- ^ a b c GRCh38: Ensembl release 89: ENSG00000105369 – Ensembl, May 2017
- ^ a b c GRCm38: Ensembl release 89: ENSMUSG00000003379 – Ensembl, May 2017
- ^ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
- ^ "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
- ^ a b c d "Entrez Gene: CD79A CD79a molecule, immunoglobulin-associated alpha".
- ^ ISBN 1-84110-100-1.
- ^ a b Online Mendelian Inheritance in Man (OMIM): 613501
- PMID 2463161.
- S2CID 22129592.
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Further reading
- Herren B, Burrows PD (2003). "B cell-restricted human mb-1 gene: expression, function, and lineage infidelity". Immunologic Research. 26 (1–3): 35–43. S2CID 38456117.
- Leduc I, Preud'homme JL, Cogné M (Oct 1992). "Structure and expression of the mb-1 transcript in human lymphoid cells". Clinical and Experimental Immunology. 90 (1): 141–6. PMID 1395095.
- Müller B, Cooper L, Terhorst C (Jun 1992). "Cloning and sequencing of the cDNA encoding the human homologue of the murine immunoglobulin-associated protein B29". European Journal of Immunology. 22 (6): 1621–5. S2CID 23910309.
- Hutchcroft JE, Harrison ML, Geahlen RL (Apr 1992). "Association of the 72-kDa protein-tyrosine kinase PTK72 with the B cell antigen receptor". The Journal of Biological Chemistry. 267 (12): 8613–9. PMID 1569106.
- Yu LM, Chang TW (Jan 1992). "Human mb-1 gene: complete cDNA sequence and its expression in B cells bearing membrane Ig of various isotypes". Journal of Immunology. 148 (2): 633–7. S2CID 24075079.
- Venkitaraman AR, Williams GT, Dariavach P, Neuberger MS (Aug 1991). "The B-cell antigen receptor of the five immunoglobulin classes". Nature. 352 (6338): 777–81. S2CID 4246284.
- Kurosaki T, Johnson SA, Pao L, Sada K, Yamamura H, Cambier JC (Dec 1995). "Role of the Syk autophosphorylation site and SH2 domains in B cell antigen receptor signaling". The Journal of Experimental Medicine. 182 (6): 1815–23. PMID 7500027.
- Lankester AC, van Schijndel GM, Cordell JL, van Noesel CJ, van Lier RA (Apr 1994). "CD5 is associated with the human B cell antigen receptor complex". European Journal of Immunology. 24 (4): 812–6. S2CID 25093082.
- Vasile S, Coligan JE, Yoshida M, Seon BK (Apr 1994). "Isolation and chemical characterization of the human B29 and mb-1 proteins of the B cell antigen receptor complex". Molecular Immunology. 31 (6): 419–27. PMID 7514267.
- Brown VK, Ogle EW, Burkhardt AL, Rowley RB, Bolen JB, Justement LB (Jun 1994). "Multiple components of the B cell antigen receptor complex associate with the protein tyrosine phosphatase, CD45". The Journal of Biological Chemistry. 269 (25): 17238–44. PMID 7516335.
- Pani G, Kozlowski M, Cambier JC, Mills GB, Siminovitch KA (Jun 1995). "Identification of the tyrosine phosphatase PTP1C as a B cell antigen receptor-associated protein involved in the regulation of B cell signaling". The Journal of Experimental Medicine. 181 (6): 2077–84. PMID 7539038.
External links
- CD79A+protein,+human at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- Human CD79A genome location and CD79A gene details page in the UCSC Genome Browser.
This article incorporates text from the United States National Library of Medicine, which is in the public domain.