Thrombin

Coagulation factor II (thrombin)
The structure of human thrombin in complex with the inhibitor hirudin.
Available structures PDB Ortholog search: PDBe, RCSB List of PDB id codes 1A2C, 1A3B, 1A3E, 1A46, 1A4W, 1A5G, 1A61, 1ABI, 1ABJ, 1AD8, 1AE8, 1AFE, 1AHT, 1AI8, 1AIX, 1AWF, 1AWH, 1AY6, 1B5G, 1B7X, 1BA8, 1BB0, 1BCU, 1BHX, 1BMM, 1BMN, 1BTH, 1C1U, 1C1V, 1C1W, 1C4U, 1C4V, 1C4Y, 1C5L, 1C5N, 1C5O, 1CA8, 1D3D, 1D3P, 1D3Q, 1D3T, 1D4P, 1D6W, 1D9I, 1DE7, 1DIT, 1DM4, 1DOJ, 1DWB, 1DWC, 1DWD, 1DWE, 1DX5, 1E0F, 1EB1, 1EOJ, 1EOL, 1FPC, 1FPH, 1G30, 1G32, 1G37, 1GHV, 1GHW, 1GHX, 1GHY, 1GJ4, 1GJ5, 1H8D, 1H8I, 1HAG, 1HAH, 1HAI, 1HAO, 1HAP, 1HBT, 1HDT, 1HGT, 1HLT, 1HUT, 1HXE, 1HXF, 1IHS, 1IHT, 1JMO, 1JOU, 1JWT, 1K21, 1K22, 1KTS, 1KTT, 1LHC, 1LHD, 1LHE, 1LHF, 1LHG, 1MH0, 1MU6, 1MU8, 1MUE, 1NM6, 1NO9, 1NRN, 1NRO, 1NRP, 1NRQ, 1NRR, 1NRS, 1NT1, 1NU7, 1NU9, 1NY2, 1NZQ, 1O0D, 1O2G, 1O5G, 1OOK, 1OYT, 1P8V, 1PPB, 1QBV, 1QHR, 1QJ1, 1QJ6, 1QJ7, 1QUR, 1RD3, 1RIW, 1SB1, 1SFQ, 1SG8, 1SGI, 1SHH, 1SL3, 1SR5, 1T4U, 1T4V, 1TA2, 1TA6, 1TB6, 1TBZ, 1THP, 1THR, 1THS, 1TMB, 1TMT, 1TMU, 1TOM, 1TQ0, 1TQ7, 1TWX, 1UMA, 1UVS, 1VR1, 1VZQ, 1W7G, 1WAY, 1WBG, 1XM1, 1XMN, 1YPE, 1YPG, 1YPJ, 1YPK, 1YPL, 1YPM, 1Z71, 1Z8I, 1Z8J, 1ZGI, 1ZGV, 1ZRB, 2A0Q, 2A2X, 2A45, 2AFQ, 2ANK, 2ANM, 2B5T, 2BDY, 2BVR, 2BVS, 2BVX, 2BXT, 2BXU, 2C8W, 2C8X, 2C8Y, 2C8Z, 2C90, 2C93, 2CF8, 2CF9, 2CN0, 2FEQ, 2FES, 2GDE, 2GP9, 2H9T, 2HGT, 2HNT, 2HPP, 2HPQ, 2HWL, 2JH0, 2JH5, 2JH6, 2OD3, 2PGB, 2PGQ, 2PKS, 2PW8, 2R2M, 2THF, 2UUF, 2UUJ, 2UUK, 2V3H, 2V3O, 2ZC9, 2ZDA, 2ZDV, 2ZF0, 2ZFF, 2ZFP, 2ZFQ, 2ZFR, 2ZG0, 2ZGB, 2ZGX, 2ZHE, 2ZHF, 2ZHQ, 2ZHW, 2ZI2, 2ZIQ, 2ZNK, 2ZO3, 3B23, 3B9F, 3BEF, 3BEI, 3BF6, 3BIU, 3BIV, 3BV9, 3C1K, 3C27, 3D49, 3DA9, 3DD2, 3DHK, 3DT0, 3DUX, 3E6P, 3EE0, 3EGK, 3EQ0, 3F68, 3GIC, 3GIS, 3HAT, 3HKJ, 3HTC, 3JZ1, 3JZ2, 3K65, 3LDX, 3LU9, 3NXP, 3P17, 3P6Z, 3P70, 3PMH, 3PO1, 3QDZ, 3QGN, 3QLP, 3QTO, 3QTV, 3QWC, 3QX5, 3R3G, 3RLW, 3RLY, 3RM0, 3RM2, 3RML, 3RMM, 3RMN, 3RMO, 3S7H, 3S7K, 3SHA, 3SHC, 3SI3, 3SI4, 3SQE, 3SQH, 3SV2, 3T5F, 3TU7, 3U69, 3U8O, 3U8R, 3U8T, 3U98, 3U9A, 3UTU, 3UWJ, 3VXE, 3VXF, 4AX9, 4AYV, 4AYY, 4AZ2, 4BAH, 4BAK, 4BAM, 4BAN, 4BAO, 4BAQ, 4BOH, 4CH2, 4CH8, 4DIH, 4DII, 4DT7, 4DY7, 4E05, 4E06, 4E7R, 4H6S, 4H6T, 4HFP, 4HTC, 4HZH, 4I7Y, 4LOY, 4LXB, 4LZ1, 4LZ4, 4MLF, 4N3L, 4NZE, 4NZQ, 4O03, 4RKJ, 4RKO, 4RN6, 4THN, 5GDS, 7KME, 8KME
Identifiers
Symbols	F2 ; PT; RPRGL2; THPH1
External IDs	OMIM: 176930 MGI: 88380 HomoloGene: 426 ChEMBL: 204 GeneCards: F2 Gene
EC number	3.4.21.5
Gene ontology Molecular function • serine-type endopeptidase activity • receptor binding • calcium ion binding • protein binding • growth factor activity • thrombospondin receptor activity Cellular component • extracellular region • extracellular space • endoplasmic reticulum lumen • Golgi lumen • cytosol • plasma membrane • extracellular matrix • extracellular exosome • blood microparticle Biological process • positive regulation of protein phosphorylation • proteolysis • acute-phase response • cell surface receptor signaling pathway • multicellular organismal development • blood coagulation • blood coagulation, intrinsic pathway • positive regulation of cell proliferation • regulation of cell shape • response to wounding • regulation of gene expression • negative regulation of platelet activation • positive regulation of phosphatidylinositol 3-kinase signaling • response to inactivity • peptidyl-glutamic acid carboxylation • platelet activation • regulation of blood coagulation • positive regulation of blood coagulation • positive regulation of cell growth • positive regulation of collagen biosynthetic process • fibrinolysis • post-translational protein modification • cellular protein metabolic process • negative regulation of proteolysis • negative regulation of astrocyte differentiation • leukocyte migration • positive regulation of release of sequestered calcium ion into cytosol • cytosolic calcium ion homeostasis • negative regulation of fibrinolysis • cellular response to mechanical stimulus • positive regulation of phospholipase C-activating G-protein coupled receptor signaling pathway • positive regulation of reactive oxygen species metabolic process Sources: Amigo / QuickGO
RNA expression pattern
More reference expression data
Orthologs
Species	Human	Mouse
Entrez	2147	14061
Ensembl	ENSG00000180210	ENSMUSG00000027249
UniProt	P00734	P19221
RefSeq (mRNA)	NM_000506	NM_010168
RefSeq (protein)	NP_000497	NP_034298
Location (UCSC)	Chr 11: 46.72 – 46.74 Mb	Chr 2: 91.63 – 91.64 Mb
PubMed search	[1]	[2]

Role of thrombin in the blood coagulation cascade

Thrombin (EC 3.4.21.5, fibrinogenase, thrombase, thrombofort, topical, thrombin-C, tropostasin, activated blood-coagulation factor II, blood-coagulation factor IIa, factor IIa, E thrombin, beta-thrombin, gamma-thrombin) is a serine protease that in humans is encoded by the F2 gene. Prothrombin (coagulation factor II) is proteolytically cleaved to form thrombin in the coagulation cascade, which ultimately results in the reduction of blood loss. Thrombin in turn acts as a serine protease that converts soluble fibrinogen into insoluble strands of fibrin, as well as catalyzing many other coagulation-related reactions.

History

After the description of fibrinogen and fibrin, Alexander Schmidt hypothesised the existence of an enzyme that converts fibrinogen into fibrin in 1872.

Physiology

Synthesis

Thrombin is produced by the enzymatic cleavage of two sites on prothrombin by activated Factor X (Xa). The activity of factor Xa is greatly enhanced by binding to activated Factor V (Va), termed the prothrombinase complex. Prothrombin is produced in the liver and is co-translationally modified in a vitamin K-dependent reaction that converts ten glutamic acids on prothrombin to gamma-carboxyglutamic acid (Gla). In the presence of calcium, the Gla residues promote the binding of prothrombin to phospholipid bilayers. Deficiency of vitamin K or administration of the anticoagulant warfarin inhibits the production of gamma-carboxyglutamic acid residues, slowing the activation of the coagulation cascade.

In human adults, the normal blood level of antithrombin activity has been measured to be around 1.1 units/mL. Newborn levels of thrombin steadily increase after birth to reach normal adult levels, from a level of around 0.5 units/mL 1 day after birth, to a level of around 0.9 units/mL after 6 months of life.

Mechanism of action

In the blood coagulation pathway, thrombin acts to convert factor XI to XIa, VIII to VIIIa, V to Va, fibrinogen to fibrin, and XIII to XIIIa.

Factor XIIIa is a transglutaminase that catalyzes the formation of covalent bonds between lysine and glutamine residues in fibrin. The covalent bonds increase the stability of the fibrin clot. Thrombin interacts with thrombomodulin.

As part of its activity in the coagulation cascade, thrombin also promotes platelet activation and aggregation via activation of protease-activated receptors on the cell membrane of the platelet.

Negative feedback

Thrombin bound to thrombomodulin activates protein C, an inhibitor of the coagulation cascade. The activation of protein C is greatly enhanced following the binding of thrombin to thrombomodulin, an integral membrane protein expressed by endothelial cells. Activated protein C inactivates factors Va and VIIIa. Binding of activated protein C to protein S leads to a modest increase in its activity. Thrombin is also inactivated by antithrombin, a serine protease inhibitor.

Protein

Anchoring of bovine prothrombin to the membrane through its Gla domain.

The molecular weight of prothrombin is approximately 72,000 Da. The catalytic domain is released from prothrombin fragment 1.2 to create the active enzyme thrombin, which has a molecular weight of 36,000 Da. Structurally, it is a member of the large PA clan of proteases.

Gene

The thrombin (prothrombin) gene is located on the eleventh chromosome (11p11-q12).

There are an estimated 30 people in the world that have been diagnosed with the congenital form of Factor II deficiency, which should not be confused with the prothrombin G20210A mutation, which is also called the factor II mutation. Prothrombin G20210A is congenital.

Prothrombin G20210A is not usually accompanied by other factor mutations (i.e., the most common is factor V Leiden). The gene may be inherited heterozygous (1 pair), or much more rarely, homozygous (2 pairs), and is not related to gender or blood type. Homozygous mutations increase the risk of thrombosis more than heterozygous mutations, but the relative increased risk is not well documented. Other potential risks for thrombosis, such as oral contraceptives may be additive. The previously reported relationship of inflammatory bowel disease (i.e., Crohn's disease or ulcerative colitis) and prothrombin G20210A or factor V Leiden mutation have been contradicted by research.

Role in disease

Activation of prothrombin is crucial in physiological and pathological coagulation. Various rare diseases involving prothrombin have been described (e.g., hypoprothrombinemia). Anti-prothrombin antibodies in autoimmune disease may be a factor in the formation of the lupus anticoagulant also known as (antiphospholipid syndrome). Hyperprothrombinemia can be caused by the G20210A mutation.

Thrombin, a potent vasoconstrictor and mitogen, is implicated as a major factor in vasospasm following subarachnoid hemorrhage. Blood from a ruptured cerebral aneurysm clots around a cerebral artery, releasing thrombin. This can induce an acute and prolonged narrowing of the blood vessel, potentially resulting in cerebral ischemia and infarction (stroke).

Beyond its key role in the dynamic process of thrombus formation, thrombin has a pronounced pro-inflammatory character, which may influence the onset and progression of atherosclerosis. Acting via its specific cell membrane receptors (protease activated receptors: PAR-1, PAR-3 and PAR-4), which are abundantly expressed in all arterial vessel wall constituents, thrombin has the potential to exert pro-atherogenic actions such as inflammation, leukocyte recruitment into the atherosclerotic plaque, enhanced oxidative stress, migration and proliferation of vascular smooth muscle cells, apoptosis and angiogenesis.

Thrombin is implicated in the physiology of blood clots. Its presence indicates the existence of a clot. In 2013 a system for detecting the presence of thrombin was developed in mice. It combines peptide-coated iron oxide attached to "reporter chemicals". When a peptide binds to a thrombin molecule, the report is released and appears in the urine where it can be detected. Human testing has not been conducted.

Applications

Research tool

Due to its high proteolytic specificity, thrombin is a valuable biochemical tool. The thrombin cleavage site (Leu-Val-Pro-Arg-Gly-Ser) is commonly included in linker regions of recombinant fusion protein constructs. Following purification of the fusion protein, thrombin can be used to selectively cleave between the Arginine and Glycine residues of the cleavage site, effectively removing the purification tag from the protein of interest with a high degree of specificity.

Medicine and surgery

Prothrombin complex concentrate and fresh frozen plasma are prothrombin-rich coagulation factor preparations that can be used to correct deficiencies (usually due to medication) of prothrombin. Indications include intractable bleeding due to warfarin.

Manipulation of prothrombin is central to the mode of action of most anticoagulants. Warfarin and related drugs inhibit vitamin K-dependent carboxylation of several coagulation factors, including prothrombin. Heparin increases the affinity of antithrombin to thrombin (as well as factor Xa). The direct thrombin inhibitors, a newer class of medication, directly inhibit thrombin by binding to its active site.

Recombinant thrombin is available as a powder for reconstitution into aqueous solution. It can be applied topically during surgery, as an aid to hemostasis. It can be useful for controlling minor bleeding from capillaries and small venules, but ineffective and not indicated for massive or brisk arterial bleeding.

Food production

Thrombin is sold under the brand name Fibrimex for use as a binding agent for meat. The thrombin in Fibrimex derives from porcine or bovine blood. According to the manufacturer it can be used to produce new kinds of mixed meats (for example combining beef and fish seamlessly). The manufacturer also states that it can be used to combine whole muscle meat, form and portion these thus cutting down on production costs without a loss in quality.

General secretary Jan Bertoft of Swedish Consumers' Association has stated that "there is danger of misleading the consumers since there is no way to tell this reconstituted meat from real meat"

See also

• Cerastocytin
• Fibrin glue
• Fibrinogen
• PA clan of proteases
• The Proteolysis Map

Further reading

• Degen S: Prothrombin. In: High K, Roberts H, eds. Molecular Basis of Thrombosis and Hemostasis. New York, NY: Marcel Dekker; 1995:75.

External links

• The MEROPS online database for peptidases and their inhibitors: S01.217
• GeneReviews/NCBI/NIH/UW entry on Prothrombin Thrombophilia
• Anti-coagulation & proteases on YouTube by The Proteolysis Map-animation
• [3] PMAP: The Proteolysis Map/Thrombin
• Thrombin: RCSB PDB Molecule of the Month