7xq8

From Proteopedia

Structure of human B-cell antigen receptor of the IgM isotype

Structural highlights

7xq8 is a 6 chain structure with sequence from Homo sapiens. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance.
Method:	Electron Microscopy, Resolution 3.3Å
Ligands:
Resources:	FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT

Disease

IGHM_HUMAN Autosomal agammaglobulinemia. The disease is caused by mutations affecting the gene represented in this entry.^[1]

Function

IGHM_HUMAN IgM antibodies play an important role in primary defense mechanisms. They have been shown to be involved in early recognition of external invaders like bacteria and viruses, cellular waste and modified self, as well as in recognition and elimination of precancerous and cancerous lesions. The membrane-bound form is found in the majority of normal B-cells alongside with IgD. Membrane-bound IgM induces the phosphorylation of CD79A and CD79B by the Src family of protein tyrosine kinases. It may cause death of cells by apoptosis. It is also found in soluble form, which represents about 30% of the total serum immunoglobulins where it is found almost exclusively as a homopentamer. After the antigen binds to the B-cell receptor, the secreted form is secreted in large amounts.^[2]

Publication Abstract from PubMed

The B cell receptor (BCR) initiates immune responses through antigen recognition. We report a 3.3-angstrom cryo-electron microscopy structure of human immunoglobulin M (IgM)-BCR in the resting state. IgM-BCR comprises two heavy chains, two light chains, and the Igalpha/Igbeta heterodimer. The ectodomains of the heavy chains closely stack against those of Igalpha/Igbeta, with one heavy chain locked between Igalpha and Igbeta in the juxtamembrane region. Extracellular interactions may determine isotype specificity of the BCR. The transmembrane helices of IgM-BCR form a four-helix bundle that appears to be conserved among all BCR isotypes. This structure contains 14 glycosylation sites on the IgM-BCR ectodomains and reveals three potential surface binding sites. Our work reveals the organizational principles of the BCR and may facilitate the design of antibody-based therapeutics.

Cryo-EM structure of the human IgM B cell receptor.,Su Q, Chen M, Shi Y, Zhang X, Huang G, Huang B, Liu D, Liu Z, Shi Y Science. 2022 Aug 19;377(6608):875-880. doi: 10.1126/science.abo3923. Epub 2022 , Aug 18. PMID:35981043^[3]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

References

↑ Yel L, Minegishi Y, Coustan-Smith E, Buckley RH, Trubel H, Pachman LM, Kitchingman GR, Campana D, Rohrer J, Conley ME. Mutations in the mu heavy-chain gene in patients with agammaglobulinemia. N Engl J Med. 1996 Nov 14;335(20):1486-93. PMID:8890099 doi:http://dx.doi.org/10.1056/NEJM199611143352003
↑ Tisch R, Roifman CM, Hozumi N. Functional differences between immunoglobulins M and D expressed on the surface of an immature B-cell line. Proc Natl Acad Sci U S A. 1988 Sep;85(18):6914-8. PMID:3137579
↑ Su Q, Chen M, Shi Y, Zhang X, Huang G, Huang B, Liu D, Liu Z, Shi Y. Cryo-EM structure of the human IgM B cell receptor. Science. 2022 Aug 19;377(6608):875-880. doi: 10.1126/science.abo3923. Epub 2022, Aug 18. PMID:35981043 doi:http://dx.doi.org/10.1126/science.abo3923