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.
Antithrombin (AT) is a small glycoprotein that inactivates several enzymes of the coagulation system. It is a 464-amino-acid protein produced by the liver. It contains three disulfide bonds and a total of four possible glycosylation sites. α-Antithrombin is the dominant form of antithrombin found in blood plasma and has an oligosaccharide occupying each of its four glycosylation sites. A single glycosylation site remains consistently un-occupied in the minor form of antithrombin, β-antithrombin. Its activity is increased manyfold by the anticoagulant drug heparin, which enhances the binding of antithrombin to factor IIa (thrombin) and factor Xa.
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 the target's active site. This contrasts with the more common competitive mechanism for protease inhibitors that bind to and block access to the protease active site.
Plasmin is an important enzyme present in blood that degrades many blood plasma proteins, including fibrin clots. The degradation of fibrin is termed fibrinolysis. In humans, the plasmin protein is encoded by the PLG gene.
Hereditary angioedema (HAE) is a disorder that results in recurrent attacks of severe swelling. The swelling most commonly affects the arms, legs, face, intestinal tract, and airway. If the intestinal tract is affected, abdominal pain and vomiting may occur. Swelling of the airway can result in its obstruction and trouble breathing. Without preventive treatment, attacks typically occur every two weeks and last for a few days.
Angioedema is an area of swelling (edema) of the lower layer of skin and tissue just under the skin or mucous membranes. The swelling may occur in the face, tongue, larynx, abdomen, or arms and legs. Often it is associated with hives, which are swelling within the upper skin. Onset is typically over minutes to hours.
The classical complement pathway is one of three pathways which activate the complement system, which is part of the immune system. The classical complement pathway is initiated by antigen-antibody complexes with the antibody isotypes IgG and IgM.
Alpha 2-antiplasmin is a serine protease inhibitor (serpin) responsible for inactivating plasmin. Plasmin is an important enzyme that participates in fibrinolysis and degradation of various other proteins. This protein is encoded by the SERPINF2 gene.
Complement C1r subcomponent is a protein involved in the complement system of the innate immune system. In humans, C1r is encoded by the C1R gene.
Complement component 1s is a protein involved in the complement system. C1s is part of the C1 complex. In humans, it is encoded by the C1S gene.
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.
Plasminogen activator inhibitor-2, a serine protease inhibitor of the serpin superfamily, is a coagulation factor that inactivates tissue plasminogen activator and urokinase. It is present in most cells, especially monocytes/macrophages. PAI-2 exists in two forms, a 60-kDa extracellular glycosylated form and a 43-kDa intracellular form.
Neutrophil elastase is a serine proteinase in the same family as chymotrypsin and has broad substrate specificity. Neutrophil elastase is secreted by neutrophils during inflammation, and 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.
Protein C inhibitor is a serine protease inhibitor (serpin) that limits the activity of protein C.
Complement factor I, also known as C3b/C4b inactivator, is a protein that in humans is encoded by the CFI gene. Complement factor I is a protein of the complement system, first isolated in 1966 in guinea pig serum, that regulates complement activation by cleaving cell-bound or fluid phase C3b and C4b. It is a soluble glycoprotein that circulates in human blood at an average concentration of 35 μg/mL.
Complement deficiency is an immunodeficiency of absent or suboptimal functioning of one of the complement system proteins. Because of redundancies in the immune system, many complement disorders are never diagnosed. Some studies estimate that less than 10% are identified. Hypocomplementemia may be used more generally to refer to decreased complement levels, while secondary complement disorder means decreased complement levels that are not directly due to a genetic cause but secondary to another medical condition.
Pancreatic secretory trypsin inhibitor (PSTI) also known as serine protease inhibitor Kazal-type 1 (SPINK1) or tumor-associated trypsin inhibitor (TATI) is a protein that in humans is encoded by the SPINK1 gene.
Ecallantide is a drug used for the treatment of hereditary angioedema (HAE) and in the prevention of blood loss in cardiothoracic surgery. It is an inhibitor of the protein kallikrein and a 60-amino acid polypeptide which was developed from a Kunitz domain through phage display to mimic antibodies inhibiting kallikrein.
Acquired C1 esterase inhibitor deficiency, also referred to as acquired angioedema (AAE), is a rare medical condition that presents as body swelling that can be life-threatening and manifests due to another underlying medical condition. The acquired form of this disease can occur from a deficiency or abnormal function of the enzyme C1 esterase inhibitor (C1-INH). This disease is also abbreviated in medical literature as C1INH-AAE. This form of angioedema is considered acquired due to its association with lymphatic malignancies, immune system disorders, or infections. Typically, acquired angioedema presents later in adulthood, in contrast to hereditary angioedema which usually presents from early childhood and with similar symptoms.
Kunitz domains are the active domains of proteins that inhibit the function of protein degrading enzymes or, more specifically, domains of Kunitz-type are protease inhibitors. They are relatively small with a length of about 50 to 60 amino acids and a molecular weight of 6 kDa. Examples of Kunitz-type protease inhibitors are aprotinin, Alzheimer's amyloid precursor protein (APP), and tissue factor pathway inhibitor (TFPI). Kunitz STI protease inhibitor, the trypsin inhibitor initially studied by Moses Kunitz, was extracted from soybeans.
