CDNA CLONING AND SEQUENCING OF RAT ALPHA-1-MACROGLOBULIN

cDNA clones coding for the plasma protease inhibitor alpha-1-macroglobulin were isolated from a rat liver library. The obtained cDNA sequence contained 4701 nucleotides and had an open reading frame coding for a 1500 amino acid long protein, including a 24 amino acid signal peptide. The identity of the deduced protein sequence as alpha-1-macroglobulin was established by comparison with published peptide sequences of the protein. The mature protein shares 53% and 57% overall amino acid identity with the two other identified members of the rat alpha-macroglobulin family, alpha-1-inhibitor 3 and alpha-2-macroglobulin. A sequence typical for an internal thiol ester was identified. Of the 24 cysteines, 23 are conserved with alpha-2-macroglobulin. However, instead of the two most C-terminal cysteines in alpha-2-macroglobulin, which forms a disulfide bridge in the receptor binding domain, alpha-1-macroglobulin contains phenylalanine. One mRNA species hybridizing with the alpha-1-macroglobulin probe was observed in rat and mouse liver RNA (approximately 6.2 kb), whereas no corresponding transcript was detected in RNA from human liver.