FGA
This gene encodes the alpha subunit of the coagulation factor fibrinogen, which is a component of the blood clot. Following vascular injury, the encoded preproprotein is proteolytically processed by thrombin during the conversion of fibrinogen to fibrin. Mutations in this gene lead to several disorders, including dysfibrinogenemia, hypofibrinogenemia, afibrinogenemia and renal amyloidosis. Alternative splicing results in multiple transcript variants, at least one of which encodes an isoform that undergoes proteolytic processing. [provided by RefSeq, Jan 2016]
Full Name
Fibrinogen Alpha Chain
Research Area
Cleaved by the protease thrombin to yield monomers which, together with fibrinogen beta (FGB) and fibrinogen gamma (FGG), polymerize to form an insoluble fibrin matrix. Fibrin has a major function in hemostasis as one of the primary components of blood clots. In addition, functions during the early stages of wound repair to stabilize the lesion and guide cell migration during re-epithelialization. Was originally thought to be essential for platelet aggregation, based on in vitro studies using anticoagulated blood. However, subsequent studies have shown that it is not absolutely required for thrombus formation in vivo. Enhances expression of SELP in activated platelets via an ITGB3-dependent pathway. Maternal fibrinogen is essential for successful pregnancy. Fibrin deposition is also associated with infection, where it protects against IFNG-mediated hemorrhage. May also facilitate the immune response via both innate and T-cell mediated pathways.
Biological Process
Adaptive immune response Source: UniProtKB-KW
Blood coagulation, common pathway Source: BHF-UCL
Blood coagulation, fibrin clot formation Source: UniProtKB
Cell-matrix adhesion Source: BHF-UCL
Cellular protein-containing complex assembly Source: BHF-UCL
Fibrinolysis Source: UniProtKB
Induction of bacterial agglutination Source: CACAO
Innate immune response Source: UniProtKB-KW
Negative regulation of blood coagulation, common pathway Source: BHF-UCL
Negative regulation of endothelial cell apoptotic process Source: BHF-UCL
Negative regulation of extrinsic apoptotic signaling pathway via death domain receptors Source: BHF-UCL
Plasminogen activation Source: UniProtKB
Platelet aggregation Source: BHF-UCL
Positive regulation of ERK1 and ERK2 cascade Source: BHF-UCL
Positive regulation of exocytosis Source: BHF-UCL
Positive regulation of heterotypic cell-cell adhesion Source: BHF-UCL
Positive regulation of peptide hormone secretion Source: BHF-UCL
Positive regulation of protein secretion Source: BHF-UCL
Positive regulation of substrate adhesion-dependent cell spreading Source: BHF-UCL
Positive regulation of vasoconstriction Source: BHF-UCL
Protein-containing complex assembly Source: UniProtKB
Protein polymerization Source: BHF-UCL
Response to calcium ion Source: BHF-UCL
Cellular Location
Secreted
Involvement in disease
Congenital afibrinogenemia (CAFBN):
The disease is caused by variants affecting the gene represented in this entry. The majority of cases of afibrinogenemia are due to truncating mutations. Variations in position Arg-35 (the site of cleavage of fibrinopeptide a by thrombin) leads to alpha-dysfibrinogenemias. Rare autosomal recessive disorder is characterized by bleeding that varies from mild to severe and by complete absence or extremely low levels of plasma and platelet fibrinogen.
Amyloidosis 8 (AMYL8):
A form of hereditary generalized amyloidosis. Clinical features include extensive visceral amyloid deposits, renal amyloidosis resulting in nephrotic syndrome, arterial hypertension, hepatosplenomegaly, cholestasis, petechial skin rash. There is no involvement of the nervous system.
Dysfibrinogenemia, congenital (DYSFIBRIN):
A disorder characterized by qualitative abnormalities (dysfibrinogenemia) of the circulating fibrinogen. Affected individuals are frequently asymptomatic, but some patients have bleeding diathesis, thromboembolic complications, or both. In some cases, dysfibrinogenemia is associated with low circulating fibrinogen levels (hypodysfibrinogenemia).
PTM
The alpha chain is normally not N-glycosylated (PubMed:23151259), even though glycosylation at Asn-686 was observed when a fragment of the protein was expressed in insect cells (PubMed:9689040). It is well known that heterologous expression of isolated domains can lead to adventitious protein modifications. Besides, glycosylation at Asn-686 is supported by large-scale glycoproteomics studies (PubMed:16335952 and PubMed:19159218), but the evidence is still quite tenuous. Most likely, Asn-686 is not glycosylated in the healthy human body, or only with low efficiency.
O-glycosylated.
Forms F13A-mediated cross-links between a glutamine and the epsilon-amino group of a lysine residue, forming fibronectin-fibrinogen heteropolymers.
About one-third of the alpha chains in the molecules in blood were found to be phosphorylated.
Conversion of fibrinogen to fibrin is triggered by thrombin, which cleaves fibrinopeptides A and B from alpha and beta chains, and thus exposes the N-terminal polymerization sites responsible for the formation of the soft clot. The soft clot is converted into the hard clot by factor XIIIA which catalyzes the epsilon-(gamma-glutamyl)lysine cross-linking between gamma chains (stronger) and between alpha chains (weaker) of different monomers.
Phosphorylated by FAM20C in the extracellular medium.
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