fibrolase

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0035821 modulation of process of another organism	IEA GO_REF:0000108	ACCEPT	Summary: This annotation correctly identifies fibrolase's role in inter-organism interaction through venom. As a venom component, fibrolase directly affects hemostasis in prey/victim organisms by degrading fibrin/fibrinogen, thus modulating coagulation processes in the target organism. Reason: Fibrolase is a venom metalloproteinase that directly affects another organism's physiology by disrupting hemostasis through fibrinolytic activity. This is a core function as it represents the primary biological role of this venom component [PMID:1898066, PMID:1304358]. Supporting Evidence: PMID:1898066 The enzyme exhibits direct fibrinolytic activity and does not activate plasminogen. In vitro studies revealed that fibrolase dissolves clots made either from purified fibrinogen or from whole blood. PMID:1304358 This is the first report of the sequence of a direct-acting, nonhemorrhagic fibrinolytic enzyme found in snake venom.
GO:0004222 metalloendopeptidase activity	IEA GO_REF:0000120	ACCEPT	Summary: This annotation correctly identifies the molecular function as a metalloendopeptidase. Fibrolase is classified as EC 3.4.24.72, a zinc metalloproteinase that cleaves peptide bonds in fibrin/fibrinogen. The term accurately captures the enzymatic mechanism. Reason: The term accurately describes the core catalytic activity - fibrolase is indeed a zinc-dependent metalloendopeptidase (EC 3.4.24.72) that hydrolyzes internal peptide bonds. This is supported by extensive biochemical characterization showing zinc dependency and specific cleavage patterns [PMID:1898066]. Supporting Evidence: PMID:1898066 the enzyme is a metalloproteinase since it is inhibited by EDTA, o-phenanthroline and tetraethylenepentamine (a specific zinc chelator). Metal analysis revealed 1 mol of zinc/mol of protein. PMID:1898066 Study of cleavage site preference of the fibrinolytic enzyme using the oxidized B chain of insulin revealed that specificity is similar to other snake venom metalloproteinases with cleavage primarily directed to an X-Leu bond.
GO:0005576 extracellular region	IEA GO_REF:0000044	ACCEPT	Summary: Correct annotation - fibrolase is a secreted venom protein found in the extracellular space after envenomation. The protein is secreted from venom glands and acts extracellularly on fibrin/fibrinogen substrates. Reason: Fibrolase is definitively a secreted protein that functions in the extracellular environment. It is produced by venom glands and secreted as part of the venom to act on extracellular targets (fibrin/fibrinogen in blood) [PMID:1304358, PMID:1898066]. Supporting Evidence: PMID:1304358 fibrolase, a fibrinolytic enzyme from southern copperhead (Agkistrodon contortrix contortrix) venom PMID:1898066 A fibrinolytic enzyme present in Agkistrodon contortrix contortrix (southern copperhead) venom has been purified
GO:0005886 plasma membrane	IEA GO_REF:0000118	REMOVE	Summary: This annotation is incorrect. Fibrolase is a secreted venom protein that acts in the extracellular space, not a plasma membrane-associated protein. There is no evidence for membrane localization. Reason: Fibrolase is a secreted soluble enzyme that functions in the extracellular environment (blood plasma) after envenomation. It has no transmembrane domains or membrane-association motifs, and all functional studies show it acting as a soluble enzyme on soluble or fibrin-bound substrates. The UniProt entry clearly states it is "Secreted" with no membrane association [PMID:1304358, PMID:1898066]. Supporting Evidence: PMID:1898066 The enzyme, fibrolase, has a molecular weight of 23,000-24,000 and an isoelectric point of pH 6.8. It is composed of approximately 200 amino acids PMID:1304358 Fibrolase is composed of 203 residues in a single polypeptide chain with a molecular weight of 22,891
GO:0006508 proteolysis	IEA GO_REF:0000120	MODIFY	Summary: Correct but could be more specific. Fibrolase performs proteolysis specifically on fibrin/fibrinogen substrates. A more specific term like 'venom-mediated fibrinolysis' (GO:0044484) would better capture the biological context. Reason: While proteolysis is correct, it's too general for this specialized venom enzyme. Fibrolase specifically performs fibrinolytic proteolysis as part of venom action. The term 'venom-mediated fibrinolysis' (GO:0044484) more accurately describes the biological process [PMID:1898066]. Proposed replacements: venom-mediated fibrinolysis Supporting Evidence: PMID:1898066 The enzyme exhibits direct fibrinolytic activity and does not activate plasminogen. In vitro studies revealed that fibrolase dissolves clots made either from purified fibrinogen or from whole blood. PMID:1304358 a direct-acting, nonhemorrhagic fibrinolytic enzyme found in snake venom
GO:0008233 peptidase activity	IEA GO_REF:0000043	REMOVE	Summary: This term is correct but too general. Fibrolase is specifically a metalloendopeptidase with defined substrate specificity, not just any peptidase. Reason: This overly broad term adds no information beyond the more specific 'metalloendopeptidase activity' (GO:0004222) already present. The general peptidase activity is redundant with the more specific metallopeptidase annotations and doesn't capture the enzyme's specific catalytic mechanism or substrate specificity [PMID:1898066]. Supporting Evidence: PMID:1898066 the enzyme is a metalloproteinase since it is inhibited by EDTA, o-phenanthroline and tetraethylenepentamine (a specific zinc chelator)
GO:0008237 metallopeptidase activity	IEA GO_REF:0000120	REMOVE	Summary: Correct annotation that captures the metal-dependent peptidase activity. However, this is somewhat redundant with the more specific 'metalloendopeptidase activity' (GO:0004222) annotation. Reason: This term is redundant with the more specific 'metalloendopeptidase activity' (GO:0004222) which better describes the enzyme's function. Metalloendopeptidase is a child term of metallopeptidase, so keeping both is unnecessary. The more specific term provides more information about the cleavage pattern (internal bonds) [PMID:1898066]. Supporting Evidence: PMID:1898066 Study of cleavage site preference of the fibrinolytic enzyme using the oxidized B chain of insulin revealed that specificity is similar to other snake venom metalloproteinases with cleavage primarily directed to an X-Leu bond.
GO:0016787 hydrolase activity	IEA GO_REF:0000043	REMOVE	Summary: This extremely broad term is technically correct but uninformative. Fibrolase has much more specific annotations that describe its actual function. Reason: This is an overly general parent term that provides no useful information beyond the specific metalloendopeptidase activity already annotated. Hydrolase activity is an ancestor of peptidase activity, which itself is an ancestor of metalloendopeptidase activity. Keeping this broad term adds no value [PMID:1898066]. Supporting Evidence: PMID:1898066 the enzyme is a metalloproteinase
GO:0046872 metal ion binding	IEA GO_REF:0000043	MODIFY	Summary: Correct but could be more specific. Fibrolase specifically binds zinc ions, not just any metal ion. The more specific term 'zinc ion binding' (GO:0008270) would be more accurate. Reason: While metal ion binding is correct, fibrolase specifically requires zinc for catalytic activity. Metal analysis confirmed 1 mol of zinc per mol of protein, and the enzyme is inhibited by zinc-specific chelators. The term 'zinc ion binding' (GO:0008270) more precisely describes this molecular function [PMID:1898066]. Proposed replacements: zinc ion binding Supporting Evidence: PMID:1898066 Metal analysis revealed 1 mol of zinc/mol of protein PMID:1898066 the enzyme is a metalloproteinase since it is inhibited by EDTA, o-phenanthroline and tetraethylenepentamine (a specific zinc chelator)
GO:0090729 toxin activity	IEA GO_REF:0000043	ACCEPT	Summary: Correct annotation. Fibrolase is a venom toxin that disrupts hemostasis in envenomated organisms through its fibrinolytic activity, representing a key component of copperhead venom's toxic effects. Reason: Fibrolase is indeed a toxin - it's a venom component that causes pathological effects in envenomated organisms by disrupting normal hemostasis through direct fibrinolysis. This is a core function as it represents the protein's primary biological role in the context of envenomation [PMID:1304358, PMID:1898066]. Supporting Evidence: PMID:1304358 fibrolase, a fibrinolytic enzyme from southern copperhead (Agkistrodon contortrix contortrix) venom PMID:1898066 A fibrinolytic enzyme present in Agkistrodon contortrix contortrix (southern copperhead) venom
GO:0044484 venom-mediated fibrinolysis	IEA	NEW	Summary: Core function of fibrolase in venom-mediated fibrinolysis Reason: Fibrolase specifically performs fibrinolytic proteolysis as part of venom action to dissolve blood clots. This biological process is core to its function but was missing from existing annotations. Supporting Evidence: PMID:1898066 A fibrinolytic enzyme present in Agkistrodon contortrix contortrix (southern copperhead) venom