Micrograph showing fibrin (dark pink amorphous material) in a blocked vein surrounded by extravasated red blood cells (right of image). An artery (left of image) and the amnion (far left of image) is also seen. Placenta in a case of fetal thrombotic vasculopathy. H&E stain.

Fibrin (also called Factor Ia) is a fibrous, non-globular protein involved in the clotting of blood. It is formed from fibrinogen by the protease thrombin, and is then polymerised to form a "mesh" that forms a hemostatic plug or clot (in conjunction with platelets) over a wound site.

Fibrin is involved in signal transduction, blood coagulation, and platelet activation.

Role in disease [link]

Excessive generation of fibrin due to activation of the coagulation cascade leads to thrombosis, the block of a vessel by an agglutination of red blood cells, platelets, polymerized fibrin and other components. Ineffective generation or premature lysis of fibrin predisposes to hemorrhage.

Dysfunction or disease of the liver can lead to a decrease in the production of fibrin's inactive precursor, fibrinogen, or to the production of abnormal fibrinogen molecules with reduced activity (dysfibrinogenaemia). Hereditary abnormalities of fibrinogen (the gene is carried on chromosome 4) are of both quantitative and qualitative in nature and include afibrinogenaemia, hypofibrinogenaemia, dysfibrinogenaemia, and hypodysfibrinogenaemia.

Consequences of reduced, absent, or dysfunctional fibrin is likely to render patients as hemophiliacs.

Physiology [link]

Cross-linking by thrombin and stabilization by activated factor XIII

Fibrin from different animal sources is generally glycosylated with complex type biantennary asparagine linked glycans. Variety is just found in the degree of core fucosylation and in the type of sialic acid and galactose linkage.^[1]

Structure [link]

Crystal structure of the double-d fragment from human fibrin

The image at the left is a crystal structure of the double-d fragment from human fibrin with two bound ligands. The experimental method used to obtain the image was X-ray diffraction, and it has a resolution of 2.30 Å. The structure is mainly made up of single alpha helices shown in red and beta sheets shown in yellow. The two blue structures are the bound ligands. The chemical structures of the ligands are Ca⁺² ion, alpha-D-mannose (C₆H₁₂O₆), and D-glucosamine (C₈H₁₅NO₆).

See also [link]

• Fibrin glue
• Fibrin scaffold

References [link]

External links [link]

• TGW1916.net, Defibrinated blood harvested from sheep (video)