Prothrombin is the circulating zymogen of alpha-thrombin, a vitamin K-dependent serine protease made in the liver and secreted into plasma. The zymogen carries an N-terminal Gla domain whose gamma-carboxyglutamate residues bind calcium and tether the protein to negatively charged phospholipid surfaces, two kringle domains, and a chymotrypsin-like protease domain. Activation by the prothrombinase complex releases alpha-thrombin, which cleaves after Arg and Lys residues to convert fibrinogen to fibrin, activates factors V, VII, VIII, XI and XIII, and, when bound to thrombomodulin, switches to an anticoagulant mode by activating protein C. Thrombin also signals to cells by cleaving protease-activated receptors on the cell surface, which exposes a tethered ligand and triggers platelet activation and calcium signalling, and C-terminal fragments released by proteolysis of thrombin act as antimicrobial host defence peptides. The protein is extracellular throughout its functional life; its interactions with cells occur at the external face of the plasma membrane.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0001530 lipopolysaccharide binding | IDA PMID:20421939 Proteolysis of human thrombin generates novel host defense p... | KEEP AS NON CORE | Summary: Thrombin-derived C-terminal peptides bind and neutralise bacterial lipopolysaccharide. Reason: The binding is a property of proteolytic fragments of thrombin acting as host defence peptides, not of the coagulation protease itself, so the claim is real but peripheral to the core function. Supporting Evidence: PMID:20421939 Here we show that C-terminal peptides of thrombin, a key enzyme in the coagulation cascade, constitute a novel class of host defense peptides, released upon proteolysis of thrombin in vitro, and detected in human wounds in vivo. |
| GO:0004175 endopeptidase activity | IEA GO_REF:0000107 | TOO GENERAL | Summary: A parent of the serine-type endopeptidase activity already asserted on direct evidence. Reason: Thrombin is a chymotrypsin-family serine protease with a defined catalytic reaction, so the specific term entails this one. Supporting Evidence: file:human/F2/F2-uniprot.txt Selective cleavage of Arg-|-Gly bonds in fibrinogen to form fibrin and release fibrinopeptides A and B. |
| GO:0004252 serine-type endopeptidase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Thrombin is a serine protease of the chymotrypsin family. Reason: The ancestral assertion is sound and human thrombin has a curated catalytic reaction with an EC number and an intact catalytic triad. Supporting Evidence: file:human/F2/F2-uniprot.txt Selective cleavage of Arg-|-Gly bonds in fibrinogen to form fibrin and release fibrinopeptides A and B. |
| GO:0004252 serine-type endopeptidase activity | IDA PMID:12855810 Modulation of alpha-thrombin function by distinct interactio... | ACCEPT | Summary: Active alpha-thrombin was used and its exosites mapped structurally. Reason: The study resolves the structure of alpha-thrombin bound to platelet glycoprotein Ibalpha through its exosites, which presupposes and uses the active protease. Supporting Evidence: PMID:12855810 We have determined the structure of platelet glycoprotein Ibalpha (GpIbalpha) bound to thrombin at 2.3 angstrom resolution |
| GO:0004252 serine-type endopeptidase activity | IDA PMID:1672265 Molecular cloning of a functional thrombin receptor reveals ... | ACCEPT | Summary: Thrombin cleaves the receptor N-terminus at a defined site. Reason: The cloning of the thrombin receptor identified the LDPR/S cleavage site used by thrombin, direct evidence of its proteolytic activity on a physiological substrate. Supporting Evidence: PMID:1672265 A putative thrombin cleavage site (LDPR/S) resembling the activation cleavage site in the zymogen protein C (LDPR/I) was noted 41 amino acids carboxyl to the receptor's start methionine. |
| GO:0004252 serine-type endopeptidase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Automated inference agreeing with the curated catalytic activity. Reason: Consistent with the experimental rows and with the EC assignment. Supporting Evidence: file:human/F2/F2-uniprot.txt Selective cleavage of Arg-|-Gly bonds in fibrinogen to form fibrin and release fibrinopeptides A and B. |
| GO:0005102 signaling receptor binding | IPI PMID:12855810 Modulation of alpha-thrombin function by distinct interactio... | ACCEPT | Summary: Thrombin binds platelet glycoprotein Ibalpha through its exosites. Reason: The crystal structure defines two GpIbalpha sites engaging exosite I and exosite II of two thrombin molecules, a genuine receptor interaction that localises thrombin on the platelet surface. Supporting Evidence: PMID:12855810 defined two sites in GpIbalpha that bind to exosite II and exosite I of two distinct alpha-thrombin molecules |
| GO:0005102 signaling receptor binding | IPI PMID:8626514 Plasminogen activator inhibitor-1 and vitronectin promote th... | ACCEPT | Summary: Thrombin is bound and cleared through the LRP1 receptor after complex formation with serpins. Reason: The interaction with a cell-surface receptor is established in this study, and receptor binding is the mechanism of thrombin clearance from the cell surface. Supporting Evidence: PMID:8626514 Plasminogen activator inhibitor-1 and vitronectin promote the cellular clearance of thrombin by low density lipoprotein receptor-related proteins |
| GO:0005509 calcium ion binding | IEA GO_REF:0000002 | ACCEPT | Summary: The Gla domain binds calcium through gamma-carboxyglutamate residues. Reason: UniProt records the gamma-carboxyglutamyl residues that bind calcium and their requirement for the calcium-dependent interaction with phospholipid surfaces, which is essential for prothrombin activation. Supporting Evidence: file:human/F2/F2-uniprot.txt The gamma-carboxyglutamyl residues, which bind calcium ions, result from the carboxylation of glutamyl residues |
| GO:0005515 protein binding | IPI PMID:14691232 Two different proteins that compete for binding to thrombin ... | REMOVE | Summary: Bare protein binding for a thermodynamic comparison of two thrombomodulin-like binders. Reason: The generic term carries no functional information. Thrombin's cofactor interaction with thrombomodulin is captured functionally by the anticoagulant regulation rows, so nothing is lost. Removal does not dispute the interaction. Supporting Evidence: PMID:10761923 Thrombomodulin, a transmembrane thrombin receptor with six contiguous epidermal growth factor-like domains (TME1-6), profoundly alters the substrate specificity of thrombin from pro- to anticoagulant by activating protein C. |
| GO:0005515 protein binding | IPI PMID:16230339 Fibrinogen substrate recognition by staphylocoagulase.(pro)t... | REMOVE | Summary: Bare protein binding for the bacterial staphylocoagulase interaction. Reason: Staphylocoagulase binding converts prothrombin into an active fibrinogen-cleaving complex without proteolytic activation, which is interesting but is not conveyed by the generic term, and no informative GO molecular function exists for it. Supporting Evidence: PMID:16230339 Fibrinogen substrate recognition by staphylocoagulase.(pro)thrombin complexes. |
| GO:0005515 protein binding | IPI PMID:16230340 Novel fluorescent prothrombin analogs as probes of staphyloc... | REMOVE | Summary: Bare protein binding for the same staphylocoagulase interaction, studied with fluorescent prothrombin analogues. Reason: Same assessment as the companion row. Supporting Evidence: PMID:16230340 Novel fluorescent prothrombin analogs as probes of staphylocoagulase-prothrombin interactions. |
| GO:0005515 protein binding | IPI PMID:3279057 Localization of protease nexin-1 on the fibroblast extracell... | REMOVE | Summary: Bare protein binding for protease nexin-1 on the fibroblast matrix. Reason: The partner is a serpin that inhibits thrombin. The generic term says nothing, and the functional content is recorded by the proteolysis-regulation rows. Supporting Evidence: PMID:3279057 Localization of protease nexin-1 on the fibroblast extracellular matrix. |
| GO:0005515 protein binding | IPI PMID:32814053 Interactome Mapping Provides a Network of Neurodegenerative ... | REMOVE | Summary: An APP hit from a large interactome mapping study. Reason: A single high-throughput interaction supports no specific molecular function, and the generic term is uninformative. Supporting Evidence: PMID:32814053 Interactome Mapping Provides a Network of Neurodegenerative Disease Proteins and Uncovers Widespread Protein Aggregation in Affected Brains. |
| GO:0005515 protein binding | IPI PMID:6323392 Mechanism of inhibition of activated protein C by protein C ... | REMOVE | Summary: Bare protein binding for inhibition by protein C inhibitor (SERPINA5). Reason: UniProt records that thrombin is inhibited by SERPINA5, which is a regulatory relationship rather than a molecular function of thrombin, and the generic term adds nothing. Supporting Evidence: file:human/F2/F2-uniprot.txt Inhibited by SERPINA5 |
| GO:0005515 protein binding | IPI PMID:8530382 Molecular cloning, expression, and partial characterization ... | REMOVE | Summary: Bare protein binding for an ovalbumin-family serpin. Reason: Another inhibitory serpin interaction with no informative molecular-function term, so the generic row is uninformative. Supporting Evidence: PMID:8530382 Molecular cloning, expression, and partial characterization of two novel members of the ovalbum |
| GO:0005515 protein binding | IPI PMID:8626514 Plasminogen activator inhibitor-1 and vitronectin promote th... | REMOVE | Summary: Bare protein binding for PAI-1 in the clearance study. Reason: The functional content of this paper, receptor-mediated clearance of thrombin, is already captured by the signaling receptor binding row for LRP1. Supporting Evidence: PMID:8626514 Plasminogen activator inhibitor-1 and vitronectin promote the cellular clearance of thrombin by low density lipoprotein receptor-related proteins |
| GO:0005515 protein binding | IPI PMID:8626514 Plasminogen activator inhibitor-1 and vitronectin promote th... | REMOVE | Summary: Bare protein binding for LRP1 in the same study. Reason: The informative version of this interaction is retained as signaling receptor binding, so the generic duplicate carries no additional information. Supporting Evidence: PMID:8626514 Plasminogen activator inhibitor-1 and vitronectin promote the cellular clearance of thrombin by low density lipoprotein receptor-related proteins |
| GO:0005515 protein binding | IPI PMID:9183005 Prothrombin, albumin and immunoglobulin A form covalent comp... | REMOVE | Summary: Bare protein binding for the covalent complex with alpha-1-microglobulin. Reason: UniProt records the plasma interaction with alpha-1-microglobulin and notes that it does not prevent prothrombin activation, so no functional molecular term follows and the generic row is uninformative. Supporting Evidence: PMID:9183005 Prothrombin, albumin and immunoglobulin A form covalent complexes with alpha1-microglobulin in |
| GO:0005576 extracellular region | HDA PMID:16502470 Human colostrum: identification of minor proteins in the aqu... | ACCEPT | Summary: Prothrombin is detected in the aqueous phase of human colostrum. Reason: A plasma protein recovered in an extracellular body fluid, consistent with the curated secreted location. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | IDA PMID:20421939 Proteolysis of human thrombin generates novel host defense p... | ACCEPT | Summary: Thrombin and its derived peptides are detected extracellularly, including in human wounds. Reason: Direct detection outside cells matches the secreted nature of the protein. Supporting Evidence: PMID:20421939 released upon proteolysis of thrombin in vitro, and detected in human wounds in vivo |
| GO:0005576 extracellular region | IDA PMID:9639571 Thrombin stimulates fibroblast procollagen production via pr... | ACCEPT | Summary: Thrombin is applied to and acts on fibroblasts from the extracellular medium. Reason: The protease acts on cells from outside, which is where the secreted protein resides. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | IEA GO_REF:0000120 | ACCEPT | Summary: Automated mapping of the curated secreted location. Reason: Prothrombin is made in the liver and secreted into plasma. Supporting Evidence: file:human/F2/F2-uniprot.txt Expressed by the liver and secreted in plasma. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-114697 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-140599 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-140664 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-140696 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-140700 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-140791 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-140840 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-140872 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-141046 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-158137 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-158419 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-379048 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-381446 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-389463 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-429529 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-5578883 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-749448 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-749452 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-8852716 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-9015379 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-9603302 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-9653249 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-9666383 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-9708859 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-9921200 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-9930790 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005576 extracellular region | TAS Reactome:R-HSA-9930792 | ACCEPT | Summary: Reactome places prothrombin or thrombin in the extracellular region, which is where the protein circulates and acts. Reason: The compartment matches the curated secreted location of this plasma protease. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005788 endoplasmic reticulum lumen | IEA GO_REF:0000117 | KEEP AS NON CORE | Summary: A transit compartment on the secretory route of this plasma protein. Reason: Prothrombin passes through the ER lumen during synthesis, gamma-carboxylation and folding in hepatocytes, so the term is correct, but the protein functions after secretion. Supporting Evidence: file:human/F2/F2-uniprot.txt Expressed by the liver and secreted in plasma. |
| GO:0005788 endoplasmic reticulum lumen | TAS Reactome:R-HSA-159826 | KEEP AS NON CORE | Summary: Reactome models gamma-carboxylation of prothrombin in the ER lumen. Reason: A biosynthetic transit location rather than the site of function. Supporting Evidence: file:human/F2/F2-uniprot.txt The modified residues are necessary for the calcium-dependent interaction with a negatively charged phospholipid surface |
| GO:0005788 endoplasmic reticulum lumen | TAS Reactome:R-HSA-159843 | KEEP AS NON CORE | Summary: Reactome models transport of prothrombin out of the ER. Reason: Transit compartment, as for the companion rows. Supporting Evidence: file:human/F2/F2-uniprot.txt Expressed by the liver and secreted in plasma. |
| GO:0005796 Golgi lumen | TAS Reactome:R-HSA-159728 | KEEP AS NON CORE | Summary: Reactome models propeptide cleavage and processing of prothrombin in the Golgi lumen. Reason: A biosynthetic transit location, correct but not where the protease acts. Supporting Evidence: file:human/F2/F2-uniprot.txt Expressed by the liver and secreted in plasma. |
| GO:0005796 Golgi lumen | TAS Reactome:R-HSA-159843 | KEEP AS NON CORE | Summary: Reactome models arrival of prothrombin in the Golgi lumen. Reason: Transit compartment, as for the companion row. Supporting Evidence: file:human/F2/F2-uniprot.txt Expressed by the liver and secreted in plasma. |
| GO:0005886 plasma membrane | TAS Reactome:R-HSA-140791 | MODIFY | Summary: Thrombin is a soluble plasma protease, not a membrane protein; it acts on substrates at the outer face of the membrane. Reason: The compartment assignment comes from reactions in which thrombin cleaves receptors or binds cofactors at the cell surface. The protein itself has no transmembrane segment or lipid anchor and is curated as secreted, so the accurate term is the external side of the plasma membrane, which the gene already carries on direct evidence. Proposed replacements: external side of plasma membrane Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005886 plasma membrane | TAS Reactome:R-HSA-140870 | MODIFY | Summary: Thrombin is a soluble plasma protease, not a membrane protein; it acts on substrates at the outer face of the membrane. Reason: The compartment assignment comes from reactions in which thrombin cleaves receptors or binds cofactors at the cell surface. The protein itself has no transmembrane segment or lipid anchor and is curated as secreted, so the accurate term is the external side of the plasma membrane, which the gene already carries on direct evidence. Proposed replacements: external side of plasma membrane Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005886 plasma membrane | TAS Reactome:R-HSA-140872 | MODIFY | Summary: Thrombin is a soluble plasma protease, not a membrane protein; it acts on substrates at the outer face of the membrane. Reason: The compartment assignment comes from reactions in which thrombin cleaves receptors or binds cofactors at the cell surface. The protein itself has no transmembrane segment or lipid anchor and is curated as secreted, so the accurate term is the external side of the plasma membrane, which the gene already carries on direct evidence. Proposed replacements: external side of plasma membrane Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005886 plasma membrane | TAS Reactome:R-HSA-141040 | MODIFY | Summary: Thrombin is a soluble plasma protease, not a membrane protein; it acts on substrates at the outer face of the membrane. Reason: The compartment assignment comes from reactions in which thrombin cleaves receptors or binds cofactors at the cell surface. The protein itself has no transmembrane segment or lipid anchor and is curated as secreted, so the accurate term is the external side of the plasma membrane, which the gene already carries on direct evidence. Proposed replacements: external side of plasma membrane Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005886 plasma membrane | TAS Reactome:R-HSA-141046 | MODIFY | Summary: Thrombin is a soluble plasma protease, not a membrane protein; it acts on substrates at the outer face of the membrane. Reason: The compartment assignment comes from reactions in which thrombin cleaves receptors or binds cofactors at the cell surface. The protein itself has no transmembrane segment or lipid anchor and is curated as secreted, so the accurate term is the external side of the plasma membrane, which the gene already carries on direct evidence. Proposed replacements: external side of plasma membrane Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0005886 plasma membrane | TAS Reactome:R-HSA-5602080 | MODIFY | Summary: Thrombin is a soluble plasma protease, not a membrane protein; it acts on substrates at the outer face of the membrane. Reason: The compartment assignment comes from reactions in which thrombin cleaves receptors or binds cofactors at the cell surface. The protein itself has no transmembrane segment or lipid anchor and is curated as secreted, so the accurate term is the external side of the plasma membrane, which the gene already carries on direct evidence. Proposed replacements: external side of plasma membrane Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0006508 proteolysis | IEA GO_REF:0000002 | ACCEPT | Summary: Thrombin's biological role is executed by proteolysis of specific substrates. Reason: The protease cleaves fibrinogen, protease-activated receptors and multiple clotting factors, so participation in proteolysis is direct and central. Supporting Evidence: file:human/F2/F2-uniprot.txt Thrombin, which cleaves bonds after Arg and Lys, converts fibrinogen to fibrin and activates factors V, VII, VIII, XIII, and, in complex with thrombomodulin, protein C. |
| GO:0006508 proteolysis | TAS PMID:7507931 Changes in the structure and function of the human thrombin ... | ACCEPT | Summary: Thrombin proteolytically activates its receptor. Reason: The cited work concerns structural and functional changes of the thrombin receptor on cleavage, which is a thrombin-catalysed proteolytic event. Supporting Evidence: PMID:1672265 A putative thrombin cleavage site (LDPR/S) resembling the activation cleavage site in the zymogen protein C (LDPR/I) was noted 41 amino acids carboxyl to the receptor's start methionine. |
| GO:0007166 cell surface receptor signaling pathway | IDA PMID:1672265 Molecular cloning of a functional thrombin receptor reveals ... | ACCEPT | Summary: Thrombin signals to cells by cleaving a cell-surface receptor. Reason: The cloning paper shows that thrombin acts on a seven-transmembrane cell-surface receptor whose cleavage generates an activating tethered ligand. The ontology does not place the thrombin-activated receptor pathway under this term, so it is a separate, true statement rather than a redundant parent. Supporting Evidence: PMID:1672265 A peptide mimicking the new amino terminus created by cleavage at R41 was a potent agonist for both thrombin receptor activation and platelet activation. |
| GO:0007186 G protein-coupled receptor signaling pathway | IEA GO_REF:0000107 | TOO GENERAL | Summary: A parent of the thrombin-activated receptor signaling pathway already asserted. Reason: Protease-activated receptors are seven-transmembrane G protein-coupled receptors, so the claim is true, but the specific thrombin term entails it and is more informative. Supporting Evidence: PMID:1672265 The deduced amino acid sequence revealed a new member of the seven transmembrane domain receptor family |
| GO:0007596 blood coagulation | IEA GO_REF:0000002 | ACCEPT | Summary: Thrombin is the central protease of the coagulation cascade. Reason: It converts fibrinogen to fibrin and activates several clotting factors, which is the defining role of the gene product. Supporting Evidence: file:human/F2/F2-uniprot.txt Thrombin, which cleaves bonds after Arg and Lys, converts fibrinogen to fibrin and activates factors V, VII, VIII, XIII, and, in complex with thrombomodulin, protein C. |
| GO:0007596 blood coagulation | TAS PMID:7592664 Inhibition of ADP-induced platelet responses by covalent mod... | ACCEPT | Summary: Author statement of the coagulation role. Reason: Independently established by the curated catalytic activity and the clinical biology of prothrombin deficiency. Supporting Evidence: file:human/F2/F2-uniprot.txt Functions in blood homeostasis, inflammation and wound healing. |
| GO:0008083 growth factor activity | TAS PMID:8626514 Plasminogen activator inhibitor-1 and vitronectin promote th... | MARK AS OVER ANNOTATED | Summary: Thrombin is mitogenic for some cells, but it is a protease acting through receptor cleavage rather than a growth factor. Reason: The mitogenic effects of thrombin are produced by proteolytic activation of protease-activated receptors, which is captured by the protease and receptor-signalling annotations. Calling the molecular function growth factor activity attributes an agonist-ligand mechanism that thrombin does not use. Supporting Evidence: PMID:10692450 These properties of thrombin rely on its action as a serine protease, which cleaves the N-terminal region of a 7-transmembrane G protein receptor (protease-activated receptor, PAR-1), thus exposing a tethered end hexapeptide sequence capable of activating its receptor. |
| GO:0008201 heparin binding | IDA PMID:20421939 Proteolysis of human thrombin generates novel host defense p... | KEEP AS NON CORE | Summary: Thrombin and its derived peptides bind glycosaminoglycans. Reason: Heparin binding through exosite II is a real property of thrombin that underlies antithrombin-mediated inhibition and surface localisation, but it is accessory to the catalytic function. Supporting Evidence: PMID:20421939 the two C-terminal, heparin-binding peptides of thrombin |
| GO:0008233 peptidase activity | IEA GO_REF:0000107 | TOO GENERAL | Summary: A parent of the serine-type endopeptidase activity already asserted. Reason: The specific catalytic term is directly supported and entails this one. Supporting Evidence: file:human/F2/F2-uniprot.txt Selective cleavage of Arg-|-Gly bonds in fibrinogen to form fibrin and release fibrinopeptides A and B. |
| GO:0009611 response to wounding | IDA PMID:9639571 Thrombin stimulates fibroblast procollagen production via pr... | KEEP AS NON CORE | Summary: Thrombin participates in the tissue response to injury, stimulating fibroblast procollagen production. Reason: A genuine role recorded by UniProt, but an organismal response downstream of the protease and receptor activities rather than a core function. Supporting Evidence: file:human/F2/F2-uniprot.txt Functions in blood homeostasis, inflammation and wound healing. |
| GO:0009897 external side of plasma membrane | IDA PMID:20421939 Proteolysis of human thrombin generates novel host defense p... | ACCEPT | Summary: Thrombin and its peptides associate with the outer face of cell and bacterial membranes. Reason: This is the correct way to record a soluble protein that acts at the cell surface. The qualifier is colocalizes_with, which matches the evidence, and the antimicrobial peptides act by membrane interaction. Supporting Evidence: PMID:20421939 these peptides exert antimicrobial effects against Gram-positive and Gram-negative bacteria, mediated by membrane lysis |
| GO:0010544 negative regulation of platelet activation | TAS PMID:17379830 Protease nexin-1 interacts with thrombomodulin and modulates... | KEEP AS NON CORE | Summary: Thrombin bound to thrombomodulin, or inhibited by protease nexin-1, restrains platelet activation. Reason: Thrombin is primarily a platelet agonist; the inhibitory role appears only in specific cofactor and inhibitor contexts, so the term is retained as non-core rather than as a core function. Both directions are recorded because they occur in different complexes. Supporting Evidence: PMID:10761923 Thrombomodulin, a transmembrane thrombin receptor with six contiguous epidermal growth factor-like domains (TME1-6), profoundly alters the substrate specificity of thrombin from pro- to anticoagulant by activating protein C. |
| GO:0030168 platelet activation | IBA GO_REF:0000033 | ACCEPT | Summary: Thrombin is the most potent physiological platelet agonist. Reason: The ancestral assertion matches direct human evidence, since cleavage of the platelet thrombin receptor generates a tethered ligand that activates platelets. Supporting Evidence: PMID:1672265 A peptide mimicking the new amino terminus created by cleavage at R41 was a potent agonist for both thrombin receptor activation and platelet activation. |
| GO:0030168 platelet activation | IDA PMID:9038223 Thrombin receptors on human platelets. Initial localization ... | ACCEPT | Summary: Thrombin receptors on platelets redistribute during thrombin-induced activation. Reason: Direct platelet experiments in which thrombin drives activation and receptor redistribution. Supporting Evidence: PMID:9038223 Platelet activation by thrombin rapidly abolished the binding of the antibodies whose epitopes are sensitive to receptor cleavage and left the platelets in a state refractory to both thrombin and the agonist peptide, SFLLRN. |
| GO:0030193 regulation of blood coagulation | TAS PMID:12855810 Modulation of alpha-thrombin function by distinct interactio... | TOO GENERAL | Summary: A parent of the positive and negative regulation terms already asserted. Reason: Both directional terms are retained in this review on direct evidence, and they entail this one, which is therefore uninformative. Supporting Evidence: PMID:12855810 Thrombin bound to platelets contributes to stop bleeding and, in pathological conditions, may cause vascular thrombosis. |
| GO:0030194 positive regulation of blood coagulation | IBA GO_REF:0000033 | ACCEPT | Summary: Thrombin amplifies its own generation and drives clot formation. Reason: It activates factors V, VIII and XI and converts fibrinogen to fibrin, so it positively regulates coagulation in addition to catalysing its central step. Supporting Evidence: PMID:10761923 The serine proteinase alpha-thrombin causes blood clotting through proteolytic cleavage of fibrinogen and protease-activated receptors and amplifies its own generation by activating the essential clotting factors V and VIII. |
| GO:0030194 positive regulation of blood coagulation | IDA PMID:9038223 Thrombin receptors on human platelets. Initial localization ... | ACCEPT | Summary: Thrombin positively regulates coagulation by amplifying its own generation and activating clotting factors. Reason: Thrombin amplifies the coagulation cascade. The GOA row's reference PMID:9038223 is cached abstract-only and documents thrombin-induced platelet activation; the direct procoagulant mechanism is quoted here from PMID:10761923, which also supports this term's IBA row. Supporting Evidence: PMID:10761923 The serine proteinase alpha-thrombin causes blood clotting through proteolytic cleavage of fibrinogen and protease-activated receptors and amplifies its own generation by activating the essential clotting factors V and VIII. |
| GO:0030195 negative regulation of blood coagulation | IDA PMID:10761923 Structural basis for the anticoagulant activity of the throm... | ACCEPT | Summary: Thrombin bound to thrombomodulin becomes an anticoagulant by activating protein C. Reason: The structure of the thrombin-thrombomodulin complex shows how cofactor binding switches substrate specificity, and activated protein C then degrades factors Va and VIIIa. Both directional annotations are correct because they describe thrombin in different complexes. Supporting Evidence: PMID:10761923 Thrombomodulin, a transmembrane thrombin receptor with six contiguous epidermal growth factor-like domains (TME1-6), profoundly alters the substrate specificity of thrombin from pro- to anticoagulant by activating protein C. |
| GO:0031012 extracellular matrix | HDA PMID:28327460 Comprehensive proteomic characterization of stem cell-derive... | KEEP AS NON CORE | Summary: Prothrombin is recovered in proteomic preparations of cell-derived extracellular matrix. Reason: A plasma protein adsorbed to or retained in matrix preparations. Credible but not functionally informative. Supporting Evidence: PMID:28327460 Comprehensive proteomic characterization of stem cell-derived extracellular matrices. |
| GO:0031012 extracellular matrix | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Coagulation proteases act in the extracellular space including the matrix around injured tissue. Reason: The inherited assertion is defensible for secreted proteases, and thrombin does act on matrix-associated substrates, but the extracellular region term already captures the functional location. Supporting Evidence: file:human/F2/F2-uniprot.txt Secreted, extracellular space. |
| GO:0032967 positive regulation of collagen biosynthetic process | IDA PMID:9639571 Thrombin stimulates fibroblast procollagen production via pr... | KEEP AS NON CORE | Summary: Thrombin stimulates fibroblast procollagen production through protease-activated receptor cleavage. Reason: A downstream cellular response to receptor activation rather than an activity of thrombin itself. Retained as non-core. Supporting Evidence: PMID:9639571 Thrombin stimulates fibroblast procollagen production via proteolytic activation of protease-ac |
| GO:0042730 fibrinolysis | IDA PMID:12855810 Modulation of alpha-thrombin function by distinct interactio... | MODIFY | Summary: Thrombin influences fibrinolysis, chiefly by activating the thrombin-activatable fibrinolysis inhibitor. Reason: Thrombin does not perform the lysis of fibrin, so the bare fibrinolysis term is the wrong one; its contribution is regulatory and mostly inhibitory, via thrombin-thrombomodulin activation of TAFI. Replace with negative regulation of fibrinolysis (GO:0051918), which thrombin genuinely does and which the gene already carries (ACCEPTed elsewhere in this review). Proposed replacements: negative regulation of fibrinolysis Supporting Evidence: PMID:10761923 The thrombin-thrombomodulin complex inhibits fibrinolysis by activating the procarboxypeptidase thrombin-acti |
| GO:0045861 negative regulation of proteolysis | IDA PMID:1695900 Alteration of serpin specificity by a protein cofactor. Vitr... | MARK AS OVER ANNOTATED | Summary: Thrombin is the protease being regulated here, not the regulator. Reason: The underlying experiments concern vitronectin changing serpin specificity towards thrombin, so thrombin is the target of the negative regulation, not the entity performing it. involved_in negative regulation of proteolysis misassigns the regulator role to the substrate, so this is an over-annotation. |
| GO:0046427 positive regulation of receptor signaling pathway via JAK-STAT | NAS PMID:10692450 Thrombin inhibits tumor cell growth in association with up-r... | KEEP AS NON CORE | Summary: An author statement about downstream signalling in tumour cells treated with thrombin. Reason: The cited study concerns thrombin inhibition of tumour cell growth with upregulation of p21; any JAK-STAT effect is a downstream cellular response to receptor cleavage, not an activity of thrombin, and the evidence is a non-traceable author statement. Retained as non-core rather than removed. Supporting Evidence: PMID:10692450 These properties of thrombin rely on its action as a serine protease, which cleaves the N-terminal region of a 7-transmembrane G protein receptor (protease-activated receptor, PAR-1) |
| GO:0048018 receptor ligand activity | IDA PMID:10761923 Structural basis for the anticoagulant activity of the throm... | MARK AS OVER ANNOTATED | Summary: Thrombin activates its receptors by cleaving them, not by acting as an agonist ligand. Reason: Protease-activated receptors are switched on by a tethered ligand that is part of the receptor's own N-terminus, exposed by thrombin cleavage, and the cited structure concerns thrombomodulin acting as a cofactor on thrombin rather than thrombin acting as its ligand. The accurate functions, serine-type endopeptidase activity and signaling receptor binding, are annotated separately. Supporting Evidence: PMID:10692450 thus exposing a tethered end hexapeptide sequence capable of activating its receptor |
| GO:0048712 negative regulation of astrocyte differentiation | IDA PMID:1691280 Reciprocal modulation of astrocyte stellation by thrombin an... | KEEP AS NON CORE | Summary: Thrombin reverses astrocyte stellation, an effect opposed by protease nexin-1. Reason: A cell-biological response to receptor cleavage in a specific cell type, well outside the coagulation role and downstream of the protease activity. Supporting Evidence: PMID:1691280 Reciprocal modulation of astrocyte stellation by thrombin and protease nexin-1. |
| GO:0050878 regulation of body fluid levels | IEA GO_REF:0000117 | TOO GENERAL | Summary: A high-level grouping that the coagulation annotations already entail. Reason: Blood coagulation, accepted here, sits under regulation of body fluid levels, so this rule-based row adds nothing. Supporting Evidence: file:human/F2/F2-uniprot.txt Functions in blood homeostasis, inflammation and wound healing. |
| GO:0051281 positive regulation of release of sequestered calcium ion into cytosol | IDA PMID:1672265 Molecular cloning of a functional thrombin receptor reveals ... | KEEP AS NON CORE | Summary: Receptor cleavage by thrombin triggers calcium mobilisation in responding cells. Reason: A second-messenger response downstream of protease-activated receptor signalling rather than an activity of thrombin. Retained as non-core. Supporting Evidence: PMID:1672265 A peptide mimicking the new amino terminus created by cleavage at R41 was a potent agonist for both thrombin receptor activation and platelet activation. |
| GO:0051281 positive regulation of release of sequestered calcium ion into cytosol | IDA PMID:19052258 Caveolin-1 scaffold domain interacts with TRPC1 and IP3R3 to... | KEEP AS NON CORE | Summary: Thrombin is used to trigger store release in this caveolin and TRPC1 study. Reason: Same assessment as the companion row; the calcium response is downstream of receptor activation. Supporting Evidence: PMID:19052258 Caveolin-1 scaffold domain interacts with TRPC1 and IP3R3 to regulate Ca2+ store release-induce |
| GO:0051480 regulation of cytosolic calcium ion concentration | IDA PMID:19052258 Caveolin-1 scaffold domain interacts with TRPC1 and IP3R3 to... | KEEP AS NON CORE | Summary: Thrombin stimulation changes cytosolic calcium in endothelial cells. Reason: Downstream of receptor cleavage, as for the store-release rows. Supporting Evidence: PMID:19052258 Caveolin-1 scaffold domain interacts with TRPC1 and IP3R3 to regulate Ca2+ store release-induce |
| GO:0051918 negative regulation of fibrinolysis | TAS PMID:17379830 Protease nexin-1 interacts with thrombomodulin and modulates... | ACCEPT | Summary: The thrombin-thrombomodulin complex activates the thrombin-activatable fibrinolysis inhibitor and so suppresses clot lysis. Reason: Thrombin itself performs the activating cleavage of procarboxypeptidase, so it does part of the work of this regulatory process. Supporting Evidence: PMID:10761923 The thrombin-thrombomodulin complex inhibits fibrinolysis by activating the procarboxypeptidase thrombin-acti |
| GO:0061844 antimicrobial humoral immune response mediated by antimicrobial peptide | IDA PMID:20421939 Proteolysis of human thrombin generates novel host defense p... | KEEP AS NON CORE | Summary: C-terminal peptides released from thrombin are antimicrobial host defence peptides. Reason: Well demonstrated, including detection in human wounds, but the activity belongs to proteolytic fragments of thrombin rather than to the coagulation protease, so it is retained as a non-core role. Supporting Evidence: PMID:20421939 these peptides exert antimicrobial effects against Gram-positive and Gram-negative bacteria, mediated by membrane lysis |
| GO:0070053 thrombospondin receptor activity | IDA PMID:2435757 Isolation of the thrombospondin membrane receptor. | REMOVE | Summary: The thrombospondin receptor isolated in this paper is an 88-kDa platelet membrane glycoprotein, not thrombin. Reason: Thrombin is a soluble plasma serine protease with no transmembrane segment and cannot be a membrane receptor. In the cited study thrombin appears only as the agonist used to stimulate platelets, while the thrombospondin binding site that was identified and isolated is a distinct 88-kDa membrane glycoprotein recognised by the OKM5 antibody, that is CD36. The annotation attributes the receptor's activity to the stimulus used in the experiment. Supporting Evidence: PMID:2435757 We have identified and isolated an 88-kd membrane glycoprotein present in platelets, endothelial cells, monocytes, and a variety of human tumor cell lines that is the membrane binding site for TSP. |
| GO:0070062 extracellular exosome | HDA PMID:23533145 In-depth proteomic analyses of exosomes isolated from expres... | KEEP AS NON CORE | Summary: Prothrombin is identified in an exosome proteome. Reason: Abundant plasma proteins are routinely recovered in vesicle preparations. Credible presence without functional implication. Supporting Evidence: PMID:23533145 In-depth proteomic analyses of exosomes isolated from expressed prostatic secretions in urine. |
| GO:0070493 thrombin-activated receptor signaling pathway | IDA PMID:11309392 Nuclear diacylglycerol kinase-theta is activated in response... | ACCEPT | Summary: Thrombin initiates protease-activated receptor signalling. Reason: Thrombin performs the cleavage step that starts the pathway, so it is a direct participant rather than merely an upstream stimulus. Supporting Evidence: PMID:1672265 A peptide mimicking the new amino terminus created by cleavage at R41 was a potent agonist for both thrombin receptor activation and platelet activation. |
| GO:0070493 thrombin-activated receptor signaling pathway | IDA PMID:7559487 Protein kinase C regulates pleckstrin by phosphorylation of ... | ACCEPT | Summary: Thrombin stimulation drives the signalling events measured in this study. Reason: Same assessment as the companion row; thrombin catalyses the activating cleavage. Supporting Evidence: PMID:1672265 A peptide mimicking the new amino terminus created by cleavage at R41 was a potent agonist for both thrombin receptor activation and platelet activation. |
| GO:0070945 neutrophil-mediated killing of gram-negative bacterium | IDA PMID:20421939 Proteolysis of human thrombin generates novel host defense p... | KEEP AS NON CORE | Summary: Thrombin-derived peptides contribute to killing of Gram-negative bacteria. Reason: The activity belongs to the released host defence peptides rather than to the coagulation protease, so it is retained as non-core. Supporting Evidence: PMID:20421939 these peptides exert antimicrobial effects against Gram-positive and Gram-negative bacteria, mediated by membrane lysis |
| GO:0072562 blood microparticle | HDA PMID:22516433 Proteomic analysis of microvesicles from plasma of healthy d... | KEEP AS NON CORE | Summary: Prothrombin is detected in plasma microvesicle proteomes. Reason: Expected for an abundant plasma protein; the detection carries no functional information. Supporting Evidence: PMID:22516433 Proteomic analysis of microvesicles from plasma of healthy donors reveals high individual varia |
| GO:1900016 negative regulation of cytokine production involved in inflammatory response | IDA PMID:20421939 Proteolysis of human thrombin generates novel host defense p... | KEEP AS NON CORE | Summary: Thrombin-derived peptides dampen macrophage responses to lipopolysaccharide. Reason: An immunomodulatory property of the released peptides, not of thrombin itself, and opposite in sign to the pro-inflammatory cytokine induction that intact thrombin produces in endothelial cells. Retained as non-core. Supporting Evidence: PMID:20421939 as well as immunomodulatory functions, by inhibiting macrophage responses to bacterial lipopolysa |
| GO:1900182 positive regulation of protein localization to nucleus | IDA PMID:11309392 Nuclear diacylglycerol kinase-theta is activated in response... | KEEP AS NON CORE | Summary: Thrombin treatment changes nuclear localisation of a signalling enzyme. Reason: A downstream cellular response to receptor activation rather than an activity of thrombin. Supporting Evidence: PMID:11309392 Nuclear diacylglycerol kinase-theta is activated in response to alpha-thrombin. |
| GO:1900738 positive regulation of phospholipase C-activating G protein-coupled receptor signaling pathway | IDA PMID:20164183 A novel protease-activated receptor-1 interactor, Bicaudal D... | KEEP AS NON CORE | Summary: Thrombin stimulation drives PAR1 signalling to phospholipase C. Reason: Correct, but a restatement of protease-activated receptor signalling in terms of a downstream effector, so it is secondary to the accepted pathway term. Supporting Evidence: PMID:20164183 A novel protease-activated receptor-1 interactor, Bicaudal D1, regulates G protein signaling an |
| GO:2000379 positive regulation of reactive oxygen species metabolic process | IDA PMID:17275676 NOX5 variants are functionally active in endothelial cells. | MARK AS OVER ANNOTATED | Summary: Thrombin stimulation increases NOX-dependent reactive oxygen species in endothelial cells. Reason: A downstream cellular response to PAR-receptor activation, several steps removed from thrombin's protease activity; thrombin does not perform ROS metabolism, so this is an over-annotation. The previous supporting text was the cited paper's title and did not support the claim, so it is removed. |
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Download this section (compressed HTML)Q: How much of thrombin's non-haemostatic biology, in inflammation, wound repair and the nervous system, is mediated by protease-activated receptors as opposed to other substrates?
Q: Are the antimicrobial C-terminal thrombin peptides generated at physiologically relevant concentrations in vivo, and by which proteases?
Q: Does thrombin bound to platelet GPIb-alpha have a distinct substrate profile from free thrombin, as thrombomodulin binding does?
Experiment: Measure cleavage kinetics of fibrinogen, PAR1 peptide and protein C by thrombin free and bound to recombinant GPIb-alpha fragments covering each exosite.
Hypothesis: GPIb-alpha binding, like thrombomodulin binding, alters thrombin substrate specificity rather than simply localising the enzyme.
Experiment: Quantify the C-terminal peptides in human wound fluid over time by targeted mass spectrometry and correlate with bacterial load, then test neutralisation with peptide-specific antibodies in an animal wound infection model.
Hypothesis: The antimicrobial activity of thrombin-derived peptides contributes to wound defence in vivo.
Experiment: Use surface biotinylation and acid washes on thrombin-stimulated platelets and endothelial cells to distinguish bound extracellular thrombin from any membrane-integrated pool, alongside PAR1 cleavage reporters.
Hypothesis: Thrombin annotations attributed to cell-surface receptor activity reflect its action on receptors rather than any membrane residence.
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