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PROSITE documentation PDOC00440 |
The proteinase-binding α-macroglobulins (A2M) [1] are large glycoproteins found in the plasma of vertebrates, in the hemolymph of some invertebrates and in reptilian and avian egg white. A2M-like proteins are able to inhibit all four classes of proteinases by a 'trapping' mechanism. They have a peptide stretch, called the 'bait region', which contains specific cleavage sites for different proteinases. When a proteinase cleaves the bait region, a conformational change is induced in the protein, thus trapping the proteinase. The entrapped enzyme remains active against low molecular weight substrates, whilst its activity toward larger substrates is greatly reduced, due to steric hindrance. Following cleavage in the bait region, a thiol ester bond, formed between the side chains of a cysteine and a glutamine, is cleaved and mediates the covalent binding of the A2M-like protein to the proteinase.
The proteins which are known to belong to this family are:
As a signature pattern for this family of proteins, we have selected the region containing the two residues involved in the thiol ester bond.
Expert(s) to contact by email: Last update:May 1991 / First entry.
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PROSITE method (with tools and information) covered by this documentation:
1 | Authors | Sottrup-Jensen L. |
Title | Alpha-macroglobulins: structure, shape, and mechanism of proteinase complex formation. | |
Source | J. Biol. Chem. 264:11539-11542(1989). | |
PubMed ID | 2473064 |