Summary: A-macroglobulin receptor
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This is the Wikipedia entry entitled "Alpha-2-Macroglobulin". More...
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Alpha-2-Macroglobulin Edit Wikipedia article
|, A2MD, CPAMD5, FWP007, S863-7, transcuprein|
alpha-2-Macroglobulin (α2M) is a large plasma protein found in the blood. It is mainly produced by the liver, and also locally synthesized by macrophages, fibroblasts, and adrenocortical cells. In humans it is encoded by the A2M gene.
Alpha 2 macroglobulin acts as an antiprotease and is able to inactivate an enormous variety of proteinases. It functions as an inhibitor of fibrinolysis by inhibiting plasmin and kallikrein. It functions as an inhibitor of coagulation by inhibiting thrombin. Alpha-2-macroglobulin may act as a carrier protein because it also binds to numerous growth factors and cytokines, such as platelet-derived growth factor, basic fibroblast growth factor, TGF-β, insulin, and IL-1β.
No specific deficiency with associated disease has been recognized, and no disease state is attributed to low concentrations of alpha-2-macroglobulin. The concentration of alpha-2-macroglobulin rises 10-fold or more in the nephrotic syndrome when other lower molecular weight proteins are lost in the urine. The loss of alpha-2-macroglobulin into urine is prevented by its large size. The net result is that alpha-2-macroglobulin reaches serum levels equal to or greater than those of albumin in the nephrotic syndrome, which has the effect of maintaining oncotic pressure.
Human alpha-2-macroglobulin is composed of four identical subunits bound together by -S-S- bonds. In addition to tetrameric forms of alpha-2-macroglobulin, dimeric, and more recently monomeric aM protease inhibitors have been identified.
Each monomer of human alpha-2-macroglobulin is composed of several functional domains, including macroglobulin domains, a thiol ester-containing domain and a receptor-binding domain. Overall, alpha-2-Macroglobulin is the largest major nonimmunoglobulin protein in human plasma.
The alpha-macroglobulin (aM) family of proteins includes protease inhibitors, typified by the human tetrameric alpha-2-macroglobulin (a2M); they belong to the MEROPS proteinase inhibitor family I39, clan IL. These protease inhibitors share several defining properties, which include (i) the ability to inhibit proteases from all catalytic classes, (ii) the presence of a 'bait region' (aka. a sequence of amino acids in an α2-macroglobulin molecule, or a homologous protein, that contains scissile peptide bonds for those proteinases that it inhibits) and a thiol ester, (iii) a similar protease inhibitory mechanism and (iv) the inactivation of the inhibitory capacity by reaction of the thiol ester with small primary amines. aM protease inhibitors inhibit by steric hindrance. The mechanism involves protease cleavage of the bait region, a segment of the aM that is particularly susceptible to proteolytic cleavage, which initiates a conformational change such that the aM collapses about the protease. In the resulting aM-protease complex, the active site of the protease is sterically shielded, thus substantially decreasing access to protein substrates. Two additional events occur as a consequence of bait region cleavage, namely (i) the h-cysteinyl-g-glutamyl thiol ester becomes highly reactive and (ii) a major conformational change exposes a conserved COOH-terminal receptor binding domain  (RBD). RBD exposure allows the aM protease complex to bind to clearance receptors and be removed from circulation. Tetrameric, dimeric, and, more recently, monomeric aM protease inhibitors have been identified.
alpha-2-Macroglobulin is able to inactivate an enormous variety of proteinases (including serine-, cysteine-, aspartic- and metalloproteinases). It functions as an inhibitor of fibrinolysis by inhibiting plasmin and kallikrein. It functions as an inhibitor of coagulation by inhibiting thrombin. Alpha-2-macroglobulin has in its structure a 35 amino acid "bait" region. Proteinases binding and cleaving the bait region become bound to α2M. The proteinase-α2M complex is recognised by macrophage receptors and cleared from the system.
alpha-2-Macroglobulin is known to bind zinc, as well as copper in plasma, even more strongly than albumin, and such it is also known as transcuprein. 10-15% of copper in human plasma is chelated by alpha-2-macroglobulin.
alpha-2-Macroglobulin levels are increased in nephrotic syndrome, a condition wherein the kidneys start to leak out some of the smaller blood proteins. Because of its size, alpha-2-macroglobulin is retained in the bloodstream. Increased production of all proteins means alpha-2-macroglobulin concentration increases. This increase has little adverse effect on the health, but is used as a diagnostic clue. Longstanding chronic renal failure can lead to amyloid by alpha-2-macroglobulin (see main article: amyloid).
alpha-2-Macroglobulin binds to and removes the active forms of the gelatinase (MMP-2 and MMP-9) from the circulation via scavenger receptors on the phagocytes.
- "Human PubMed Reference:".
- "Mouse PubMed Reference:".
- Andersen GR, Koch TJ, Dolmer K, Sottrup-Jensen L, Nyborg J (October 1995). "Low resolution X-ray structure of human methylamine-treated alpha 2-macroglobulin". J. Biol. Chem. 270 (42): 25133–41. doi:10.1074/jbc.270.42.25133. PMID 7559647.
- Sottrup-Jensen L, Stepanik TM, Kristensen T, Wierzbicki DM, Jones CM, Lønblad PB, et al. (1984). "Primary structure of human alpha 2-macroglobulin. V. The complete structure.". J Biol Chem. 259 (13): 8318–27. PMID 6203908.
- Dodds AW, Law SK (December 1998). "The phylogeny and evolution of the thioester bond-containing proteins C3, C4 and alpha 2-macroglobulin". Immunol. Rev. 166: 15–26. doi:10.1111/j.1600-065X.1998.tb01249.x. PMID 9914899.
- Armstrong PB, Quigley JP (1999). "Alpha2-macroglobulin: an evolutionarily conserved arm of the innate immune system". Dev. Comp. Immunol. 23 (4-5): 375–90. doi:10.1016/s0145-305x(99)00018-x. PMID 10426429.
- Doan N, Gettins PG (2007). "Human alpha2-macroglobulin is composed of multiple domains, as predicted by homology with complement component C3.". Biochem J. 407 (1): 23–30. doi:10.1042/BJ20070764. PMC . PMID 17608619.
- Sottrup-Jensen L (July 1989). "Alpha-macroglobulins: structure, shape, and mechanism of proteinase complex formation". J. Biol. Chem. 264 (20): 11539–42. PMID 2473064.
- Enghild JJ, Salvesen G, Thøgersen IB, Pizzo SV (July 1989). "Proteinase binding and inhibition by the monomeric alpha-macroglobulin rat alpha 1-inhibitor-3". J. Biol. Chem. 264 (19): 11428–35. PMID 2472396.
- Enghild JJ, Thøgersen IB, Roche PA, Pizzo SV (February 1989). "A conserved region in alpha-macroglobulins participates in binding to the mammalian alpha-macroglobulin receptor". Biochemistry. 28 (3): 1406–12. doi:10.1021/bi00429a069. PMID 2469470.
- Van Leuven F, Cassiman JJ, Van den Berghe H (December 1986). "Human pregnancy zone protein and alpha 2-macroglobulin. High-affinity binding of complexes to the same receptor on fibroblasts and characterization by monoclonal antibodies". J. Biol. Chem. 261 (35): 16622–5. PMID 2430968.
- de Boer JP, Creasey AA, Chang A, Abbink JJ, Roem D, Eerenberg AJ, Hack CE, Taylor FB (December 1993). "Alpha-2-macroglobulin functions as an inhibitor of fibrinolytic, clotting, and neutrophilic proteinases in sepsis: studies using a baboon model". Infect. Immun. 61 (12): 5035–43. PMC . PMID 7693593.
- Liu, Nanmei; Lo, Louis Shi-li; Askary, S. Hassan; Jones, LaTrice; Kidane, Theodros Z.; Nguyen, Trisha Trang Minh; Goforth, Jeremy; Chu, Yu-Hsiang; Vivas, Esther; Tsai, Monta; Westbrook, Terence; Linder, Maria C. (September 2007). "Transcuprein is a macroglobulin regulated by copper and iron availability". The Journal of Nutritional Biochemistry. 18 (9): 597–608. doi:10.1016/j.jnutbio.2006.11.005.
- Liu, Nan-mei; Nguyen, Trang; Kidane, Theodros; Moriya, Mizue; Goforth, Jeremy; Chu, Andy; Linder, Maria (6 March 2006). "Transcupreins are serum copper-transporters of the macroglobulin family, and may be regulated by iron and copper". The FASEB Journal. 20 (4): A553–A554. ISSN 0892-6638.
- Blacker D, Wilcox MA, Laird NM, Rodes L, Horvath SM, Go RC, Perry R, Watson B, Bassett SS, McInnis MG, Albert MS, Hyman BT, Tanzi RE (August 1998). "Alpha-2 macroglobulin is genetically associated with Alzheimer disease". Nat. Genet. 19 (4): 357–60. doi:10.1038/1243. PMID 9697696.
- Kovacs DM (July 2000). "alpha2-macroglobulin in late-onset Alzheimer's disease". Exp. Gerontol. 35 (4): 473–9. doi:10.1016/S0531-5565(00)00113-3. PMID 10959035.
- McPherson & Pincus: Henry's Clinical Diagnosis and Management by Laboratory Methods, 21st ed.
- Firestein: Kelley's Textbook of Rheumatology, 8th edition.
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A-macroglobulin receptor Provide feedback
This family includes the receptor domain region of the alpha-2-macroglobulin family.
Zanotti G, Bassetto A, Battistutta R, Folli C, Arcidiaco P, Stoppini M, Berni R; , Biochim Biophys Acta 2000;1478:232-238.: Structure at 1.44 A resolution of an N-terminally truncated form of the rat serum complement C3d fragment. PUBMED:10825534 EPMC:10825534
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR009048
This entry represents the receptor-binding domain (RBD) of alpha-2-macroglobulin proteins. The RBD is located at the C terminus, its structure having an immunoglobulin-like fold consists of a sandwich of nine strands in two sheets with a Greek-key topology [PUBMED:11106161, PUBMED:9634697].
The alpha-macroglobulin (aM) family of proteins includes protease inhibitors [PUBMED:2473064], typified by the human tetrameric a2-macroglobulin (a2M); they belong to the MEROPS proteinase inhibitor family I39, clan IL. These protease inhibitors share several defining properties, which include (i) the ability to inhibit proteases from all catalytic classes, (ii) the presence of a 'bait region' and a thiol ester, (iii) a similar protease inhibitory mechanism and (iv) the inactivation of the inhibitory capacity by reaction of the thiol ester with small primary amines. aM protease inhibitors inhibit by steric hindrance [PUBMED:2472396]. The mechanism involves protease cleavage of the bait region, a segment of the aM that is particularly susceptible to proteolytic cleavage, which initiates a conformational change such that the aM collapses about the protease. In the resulting aM-protease complex, the active site of the protease is sterically shielded, thus substantially decreasing access to protein substrates. Two additional events occur as a consequence of bait region cleavage, namely (i) the h-cysteinyl-g-glutamyl thiol ester becomes highly reactive and (ii) a major conformational change exposes a conserved COOH-terminal receptor binding domain [PUBMED:2469470] (RBD). RBD exposure allows the aM protease complex to bind to clearance receptors and be removed from circulation [PUBMED:2430968]. Tetrameric, dimeric, and, more recently, monomeric aM protease inhibitors have been identified [PUBMED:9914899, PUBMED:10426429].
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Cellular component||extracellular region (GO:0005576)|
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1Cannot generate PP/Heatmap alignments for seeds; no PP data available
Key: available, not generated, — not available.
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|Number in seed:||277|
|Number in full:||1611|
|Average length of the domain:||87.80 aa|
|Average identity of full alignment:||30 %|
|Average coverage of the sequence by the domain:||6.54 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 26740544 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||13|
|Download:||download the raw HMM for this family|
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Unmapped species names
The tree is built by looking at each sequence in the full alignment for the family. We take the name of the species given by UniProt and try to map that to the full taxonomic tree from NCBI. In some cases, the name chosen by UniProt does not map to any node in the NCBI tree, perhaps because the chosen name is listed as a synonym or a misspelling in the NCBI taxonomy.
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The tree shows the occurrence of this domain across different species. More...
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For all of the domain matches in a full alignment, we count the number that are found on all sequences in the alignment. This total is shown in the purple box.
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We use the NCBI species tree to group organisms according to their taxonomy and this forms the structure of the displayed tree. Note that in some cases the trees are too large (have too many nodes) to allow us to build an interactive tree, but in most cases you can still view the tree in a plain text, non-interactive representation. Those species which are represented in the seed alignment for this domain are highlighted.
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There are 13 interactions for this family. More...
We determine these interactions using iPfam, which considers the interactions between residues in three-dimensional protein structures and maps those interactions back to Pfam families. You can find more information about the iPfam algorithm in the journal article that accompanies the website.
For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the A2M_recep domain has been found. There are 85 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.
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