The domain within your query sequence starts at position 49 and ends at position 193; the E-value for the Fib_alpha domain shown below is 1.29e-69.



Fibrinogen alpha/beta chain family
SMART accession number:SM01212
Description: Fibrinogen is a protein involved in platelet aggregation and is essential for the coagulation of blood. This domain forms part of the central coiled coiled region of the protein which is formed from two sets of three non-identical chains (alpha, beta and gamma).
Interpro abstract (IPR012290):

Fibrinogen plays key roles in both blood clotting and platelet aggregation. During blood clot formation, the conversion of soluble fibrinogen to insoluble fibrin is triggered by thrombin, resulting in the polymerisation of fibrin, which forms a soft clot; this is then converted to a hard clot by factor XIIIA, which cross-links fibrin molecules. Platelet aggregation involves the binding of the platelet protein receptor integrin alpha(IIb)-beta(3) to the C-terminal D domain of fibrinogen [ (PUBMED:12799374) ]. In addition to platelet aggregation, platelet-fibrinogen interaction mediates both adhesion and fibrin clot retraction.

Fibrinogen occurs as a dimer, where each monomer is composed of three non-identical chains, alpha, beta and gamma, linked together by several disulphide bonds [ (PUBMED:11460466) ]. The N-terminals of all six chains come together to form the centre of the molecule (E domain), from which the monomers extend in opposite directions as coiled coils, followed by C-terminal globular domains (D domains). Therefore, the domain composition is: D-coil-E-coil-D. At each end, the C-terminal of the alpha chain extends beyond the D domain as a protuberance that is important for cross-linking the molecule.

During clot formation, the N-terminal fragments of the alpha and beta chains (within the E domain) in fibrinogen are cleaved by thrombin, releasing fibrinopeptides A and B, respectively, and producing fibrin. This cleavage results in the exposure of four binding sites on the E domain, each of which can bind to a D domain from different fibrin molecules. The binding of fibrin molecules produces a polymer consisting of a lattice network of fibrins that form a long, branching, flexible fibre [ (PUBMED:11593005) (PUBMED:15837518) ]. Fibrin fibres interact with platelets to increase the size of the clot, as well as with several different proteins and cells, thereby promoting the inflammatory response and concentrating the cells required for wound repair at the site of damage.

This entry represents the coiled-coil domain and part of the N-terminal E domain found in all three fibrinogen polypeptides, namely the alpha, beta and gamma chains.

GO process:platelet activation (GO:0030168), protein polymerization (GO:0051258)
GO component:fibrinogen complex (GO:0005577)
GO function:signaling receptor binding (GO:0005102)
Family alignment:
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There are 882 Fib_alpha domains in 870 proteins in SMART's nrdb database.

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