Nucleotide sequence of cDNA encoding human alpha 2-macroglobulin and assignment of the chromosomal locus.

Abstract

Six a2-macroglobulin (a2M) cDNA clones were isolated from a human liver cDNA library by using synthetic oligonucleotides as hybridization probes. One of these, pa2M1, carries a 4.6-kilobase-pair insert, which was sequenced. The insert contains the coding sequences for the mature a2M polypeptide (1451 amino acids) and for a 23-amino acid signal peptide at the NH2 terminus of the precursor proa2M. At the 3' end of the insert a poly(A) addition signal A-A-T-A-A-A and part of the poly(A) tail of the messenger RNA were found. The protein sequence deduced from the nucleotide sequence agrees with the published a2M amino acid sequence for all except three residues. The a2M locus was assigned to human chromosome 12 by Southern blot analysis with DNA from a panel of mouse/human somatic cell hybrids, using a2M cDNA as a hybridization probe.a2-Macroglobulin (a2M) is a serum glycoprotein and a major plasma proteinase inhibitor with a wide specificity. a2M-related proteins are present in all vertebrate species (1-4). Human a2M is a tetramer of four identical 185-kDa subunits, arranged as a pair of dimers each consisting of two disulfidelinked monomers (5, 6). The a2M polypeptide has a so-called bait region and an internal thiol ester bond, which account for its properties as a proteinase inhibitor. The bait region, composed of a series of target peptide bonds for plasma proteinases (7, 8) (13,14).This suggests that the conformational change, which accompanies the complex formation between a2M and proteinases and the hydrolysis of the thiol ester bond, exposes regions of the a2M molecule that are recognized by these receptors. Receptor-mediated endocytosis of proteinase-a2M complexes by macrophages and liver cells leads to clearance of the complexes from the circulation.Internal thiol ester bonds are also found in the complement proteins C3 and C4 (15), which are derived from precursor polypeptides of size similar to a2M (180-200 kDa). Their thiol ester sites are found in positions comparable to those in a2M, and the amino acid sequences of all three thiol ester sites are conserved. These observations led to the proposal that the C3, C4, and a2M genes are derived from a common ancestral gene (16). The sequences of murine and human C3 and human C4 and partial cDNA sequences of murine C4 have recently been determined (17-21). Comparison of human a2M with murine C3 revealed a 25% overall sequence homology (17,18,22

Localization of the Binding Site for Transforming Growth Factor-β in Human α2-Macroglobulin to a 20-kDa Peptide That Also Contains the Bait Region

“…Preparation of Constructs Encoding GST-␣ 2 M-Peptide Fusion Proteins-The human ␣ 2 M cDNA in pAT153/PvuII/8 (pAT-␣ 2 M) was obtained from the ATCC (16). Restriction digest analysis revealed an additional SacI cleavage site, which was not predicted by the published sequence (16), due to a single base substitution at nucleotide 2431 (C 3 T).…”

Identification and sequencing of cDNA clones for the rodent negative acute‐phase protein α1‐inhibitor 3

“…Approximately 70% homology at the amino acid level is revealed by a comparison of pI3cDNA6 sequence with the partially known rat a2-macroglobulin sequence [4, 121. A similar degree of homology was found to the human a2-macroglobulin for which both the complete amino acid [15] and cDNA sequences [16] have been published.…”

Synthesis and secretion of α2‐macroglobulin by human hepatocytes in culture

“…Thus, hepatocytes exhibit a2-M receptors and the removal of the a2-M-proteinase complex is mainly accounted for by hepatocytes [21,22]. Furthermore, malignant cell lines and tumours of hepatic origin synthesize ~(2-M and recently M~-M-cDNA was isolated from human liver [ 19,20,29].…”