Title: Primary structure of human alpha 2-antiplasmin, a serine protease inhibitor (serpin).
Abstract: The plasma protein a,-antiplasmin is the main physiological inhibitor of the serine protease plasmin, which is responsible for the dissolution of fibrin clots.We have determined the primary structure of mature human a2-antiplasmin by DNA sequencing of overlapping cDNA fragments prepared from human liver mRNA.cDNA clones were identified by hybridization with a 48-base pair deoxyoligonucleotide probe deduced from the sequence of a 16-amino acid peptide of a,-antiplasmin.Mature human a,-antiplasmin contains 452 amino acids.It is homologous (2348%) with five other proteins belonging to the serine protease inhibitor (serpin) superfamily.Its reactive site, Le. the peptide bond cleaved by reaction with its primary target enzyme, plasmin, consists of ArgS64-Met366.This dipeptide corresponds to the reactive site Met36s-Ser36s of the archetypal serpin, al-antitrypsin. ~~~Serine proteases play a key role in the biochemical pathways responsible for such biological phenomena as fibrin formation and its dissolution, complement activation, and inflammation.These pathways are composed of inactive zymogens which, by limited enzymatic hydrolysis, are converted to active serine proteases, capable of a variety of specific and nonspecific functions.Uncontrolled proteolysis which can lead to system collapse is opposed by the presence in plasma of specific inhibitors.Congenital deficiencies of these inhibitors are associated with serious disease states.Structural homology between a,-antitrypsin (al-protease inhibitor), human antithrombin 111, and chicken ovalbumin was first recognized by Hunt and Dayhoff (1) and subsequently extended to human a,-antichymotrypsin (2), rat angiotensinogen (3), barley protein Z (4), mouse contrapsin ( 5 ) , and human a,-antiplasmin (6).Ci-inhibitor has been shown to be functionally homologous (7).This superfamily of serine protease inhibitors has recently been termed serpins (8).The serpins react with their target enzymes by presenting substrate-like regions allowing direct binding of the enzyme (9).Their reactive sites contain an amino acid designated the P1 residue (lo), that is specifically recognized by the active site of the target serine protease.A very stable 1:l stoichiometric enzymatically inactive complex is then formed, resulting in Onderzoeksactie (Projects 80-85/3 and 85-90/78).The costs of pub-