Hmdb loader
HMDB Protein ID HMDBP12428
Secondary Accession Numbers None
Name Immunoglobulin heavy constant mu
  1. Ig mu chain C region
  2. Ig mu chain C region BOT
  3. Ig mu chain C region GAL
  4. Ig mu chain C region OU
Gene Name IGHM
Protein Type Unknown
Biological Properties
General Function Not Available
Specific Function Constant region of immunoglobulin heavy chains. Immunoglobulins, also known as antibodies, are membrane-bound or secreted glycoproteins produced by B lymphocytes. In the recognition phase of humoral immunity, the membrane-bound immunoglobulins serve as receptors which, upon binding of a specific antigen, trigger the clonal expansion and differentiation of B lymphocytes into immunoglobulins-secreting plasma cells. Secreted immunoglobulins mediate the effector phase of humoral immunity, which results in the elimination of bound antigens (PubMed:22158414, PubMed:20176268). The antigen binding site is formed by the variable domain of one heavy chain, together with that of its associated light chain. Thus, each immunoglobulin has two antigen binding sites with remarkable affinity for a particular antigen. The variable domains are assembled by a process called V-(D)-J rearrangement and can then be subjected to somatic hypermutations which, after exposure to antigen and selection, allow affinity maturation for a particular antigen (PubMed:17576170, PubMed:20176268). 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 (PubMed:3137579, PubMed:16895553).
Pathways Not Available
Reactions Not Available
GO Classification
Biological Process
B cell receptor signaling pathway
defense response to bacterium
leukocyte migration
complement activation, classical pathway
phagocytosis, engulfment
phagocytosis, recognition
positive regulation of B cell activation
innate immune response
adaptive immune response
defense response to Gram-negative bacterium
antibacterial humoral response
Cellular Component
cell surface
extracellular vesicular exosome
plasma membrane
blood microparticle
hexameric IgM immunoglobulin complex
immunoglobulin complex, circulating
pentameric IgM immunoglobulin complex
extracellular space
external side of plasma membrane
integral to membrane
Molecular Function
antigen binding
Cellular Location Not Available
Gene Properties
Chromosome Location Not Available
Locus Not Available
SNPs Not Available
Gene Sequence Not Available
Protein Properties
Number of Residues Not Available
Molecular Weight 49439.37
Theoretical pI Not Available
Pfam Domain Function
Signals Not Available
Transmembrane Regions Not Available
Protein Sequence Not Available
GenBank ID Protein Not Available
UniProtKB/Swiss-Prot ID P01871
UniProtKB/Swiss-Prot Entry Name IGHM_HUMAN
GenBank Gene ID Not Available
GeneCard ID Not Available
GenAtlas ID Not Available
HGNC ID Not Available
General References
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  6. Putnam FW, Florent G, Paul C, Shinoda T, Shimizu A: Complete amino acid sequence of the Mu heavy chain of a human IgM immunoglobulin. Science. 1973 Oct 19;182(4109):287-91. doi: 10.1126/science.182.4109.287. [PubMed:4742735 ]
  7. Geisberger R, Lamers M, Achatz G: The riddle of the dual expression of IgM and IgD. Immunology. 2006 Aug;118(4):429-37. doi: 10.1111/j.1365-2567.2006.02386.x. [PubMed:16895553 ]
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  11. Watanabe S, Barnikol HU, Horn J, Bertram J, Hilschmann N: [The primary structure of a monoclonal IgM-immunoglobulin (macroglobulin Gal.), II: the amino acid sequence of the H-chain (mu-type), subgroup H III. Architecture of the complete IgM-molecule (author's transl)]. Hoppe Seylers Z Physiol Chem. 1973 Oct-Nov;354(10-11):1505-9. [PubMed:4803843 ]
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  14. Friedlander RM, Nussenzweig MC, Leder P: Complete nucleotide sequence of the membrane form of the human IgM heavy chain. Nucleic Acids Res. 1990 Jul 25;18(14):4278. doi: 10.1093/nar/18.14.4278. [PubMed:2115996 ]
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  16. Dolby TW, Devuono J, Croce CM: Cloning and partial nucleotide sequence of human immunoglobulin mu chain cDNA from B cells and mouse-human hybridomas. Proc Natl Acad Sci U S A. 1980 Oct;77(10):6027-31. doi: 10.1073/pnas.77.10.6027. [PubMed:6777778 ]
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  18. 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. doi: 10.1073/pnas.85.18.6914. [PubMed:3137579 ]
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