A protease is an enzyme that catalyzes proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids. They do this by cleaving the peptide bonds within proteins by hydrolysis, a reaction where water breaks bonds. Proteases are involved in many biological functions, including digestion of ingested proteins, protein catabolism, and cell signalling.
Alpha-1 antitrypsin or α1-antitrypsin is a protein belonging to the serpin superfamily. It is encoded in humans by the SERPINA1 gene. A protease inhibitor, it is also known as alpha1–proteinase inhibitor (A1PI) or alpha1-antiproteinase (A1AP) because it inhibits various proteases. In older biomedical literature it was sometimes called serum trypsin inhibitor, because its capability as a trypsin inhibitor was a salient feature of its early study. As a type of enzyme inhibitor, it protects tissues from enzymes of inflammatory cells, especially neutrophil elastase, and has a reference range in blood of 0.9–2.3 g/L, but the concentration can rise manyfold upon acute inflammation.
Transcortin, also known as corticosteroid-binding globulin (CBG) or serpin A6, is a protein produced in the liver in animals. In humans it is encoded by the SERPINA6 gene. It is an alpha-globulin.
In biology and biochemistry, protease inhibitors, or antiproteases, are molecules that inhibit the function of proteases. Many naturally occurring protease inhibitors are proteins.
Serpins are a superfamily of proteins with similar structures that were first identified for their protease inhibition activity and are found in all kingdoms of life. The acronym serpin was originally coined because the first serpins to be identified act on chymotrypsin-like serine proteases. They are notable for their unusual mechanism of action, in which they irreversibly inhibit their target protease by undergoing a large conformational change to disrupt its active site. This contrasts with the more common competitive mechanism for protease inhibitors that bind to and block access to the protease active site.
C1-inhibitor is a protease inhibitor belonging to the serpin superfamily. Its main function is the inhibition of the complement system to prevent spontaneous activation but also as the major regulator of the contact system. C1-inhibitor is an acute-phase protein that circulates in blood at levels of around 0.25 g/L. The levels rise ~2-fold during inflammation. C1-inhibitor irreversibly binds to and inactivates C1r and C1s proteases in the C1 complex of classical pathway of complement. MASP-1 and MASP-2 proteases in MBL complexes of the lectin pathway are also inactivated. This way, C1-inhibitor prevents the proteolytic cleavage of later complement components C4 and C2 by C1 and MBL. Although named after its complement inhibitory activity, C1-inhibitor also inhibits proteases of the fibrinolytic, clotting, and kinin pathways. Note that C1-inhibitor is the most important physiological inhibitor of plasma kallikrein, fXIa, and fXIIa.
Heparin cofactor II (HCII), a protein encoded by the SERPIND1 gene, is a coagulation factor that inhibits IIa, and is a cofactor for heparin and dermatan sulfate.
Neutrophil elastase is a serine proteinase in the same family as chymotrypsin and has broad substrate specificity. Secreted by neutrophils and macrophages during inflammation, it destroys bacteria and host tissue. It also localizes to neutrophil extracellular traps (NETs), via its high affinity for DNA, an unusual property for serine proteases.
Alpha 1-antichymotrypsin is an alpha globulin glycoprotein that is a member of the serpin superfamily. In humans, it is encoded by the SERPINA3 gene.
Protein C inhibitor is a serine protease inhibitor (serpin) that limits the activity of protein C.
Glia-derived nexin is a protein that in humans is encoded by the SERPINE2 gene.
Serpin B6 is a protein that in humans is encoded by the SERPINB6 gene.
Leukocyte elastase inhibitor (LEI) also known as serpin B1 is a protein that in humans is encoded by the SERPINB1 gene. It is a member of the clade B serpins or ov-serpins founded by ovalbumin.
Serpin B13 is a protein that in humans is encoded by the SERPINB13 gene.
Serpin B8 is a protein that in humans is encoded by the SERPINB8 gene.
Kallistatin is a protein that in humans is encoded by the SERPINA4 gene.
Serpin A9 also known as centerin or GCET1 is a protein that in humans is encoded by the SERPINA9 gene located on chromosome 14q32.1. Serpin A9 is a member of the serpin family of serine protease inhibitors.
Uterine serpins are members of the A clade of the serine protease inhibitor (serpin) superfamily of proteins and are encoded by the SERPINA14 gene. Uterine serpins are produced by the endometrium of a restricted group of mammals under the influence of progesterone or estrogen. These proteins appear to be inactive protease inhibitors and may function during pregnancy to regulate immune function or participate in transplacental transport.
Serpin peptidase inhibitor, clade B (ovalbumin), member 10 is a protein that in humans is encoded by the SERPINB10 gene.
Serpin A12 is a glycoprotein that in humans is encoded by the SERPINA12 gene. It is encoded by the SERPIN A12 gene and it is included inside the serine protease inhibitor (serpin) family, class A serpin specifically.
