Tissue factor
- OMIM: 134390
- UniProt: P13726
- MGI: 88381
Tissue factor ( factor III or tissue thromboplastin also, Eng. Well as tissue factor ) is a protein involved in blood clotting. Therefore it is included in the group of coagulation factors. It is located in the tissue ( subendothelium ), in platelets and leukocytes ( white blood cells).
Genetics
The gene for the tissue factor is located on chromosome 1 p22 p21 gene locus.
Construction
Tissue factor is a protein that consists of three domains:
A first domain, which is outside the cell. This binds through protein-protein interactions to the activated Proconvertin (factor VIIa). Proconvertin also consists of different domains. One of these domains, the γ - carboxylated carboxyglutamate domain, binds in the presence of calcium to negatively charged phospholipids. This increases the binding protein-protein bonding between proconvertin and Thrombokinase (factor X).
A second domain that penetrates the membrane hydrophobic.
3, a domain of 21 amino acids in length within the cell, which takes over the functions of signal thromboplastin.
Function
Tissue factor is the receptor on the cell membrane of activated Proconvertin (factor VIIa).
The most explored function of tissue factor is its role in blood clotting. The complex of tissue factor with Proconvertin catalyzes the conversion of the inactive Stuart - Prower factor ( factor X) to activated factor Xa. Proconvertin forms together with the tissue factor to the extrinsic pathway of blood coagulation, in which a violation of the blood vessels to be eliminated as quickly as possible through the blood coagulation (see hemostasis ). This is offset by the intrinsic pathway, in which the Stuart - Prower factor is activated by a cascade of already in the blood factors.
In addition, the tissue factor belongs to a group of proteins that are grouped under the generic term " cytokine receptor class II". The members of this group of cytokines, small proteins that affect the behavior of the white blood cells is activated. Furthermore, it was found that the binding of activated Proconvertin the tissue factor signaling processes within the cell triggers. These signaling processes play a role in the formation of new blood vessels (angiogenesis) and in the inhibition of programmed cell death (apoptosis).
Occurrence
Tissue factor is expressed by cells that are not normally associated with flowing blood in the compound, such as for example cells in the subendothelium ( connective tissue ) and the cells that surround blood vessels (e.g., fibroblasts). That changes when the blood vessels are damaged (eg by injury ). The cells with Thrombokinase come into contact with Proconvertin that circulates in the blood. This thousand-fold the activity of the Proconvertins.
The inner wall of blood vessels is composed of endothelial cells, which form the only tissue factor when they are exposed to anti -forming molecules, such as tumor necrosis factor alpha (TNF- alpha). Also monocytes form the tissue factor out after contact with anti- forming molecules.
Tissue factor can also be found on circulating microparticles. Which are membrane vesicles, which are composed of membrane fragments that are released from various cells such as blood platelets or monocytes. They are loaded with tissue factor, and other proteins such as adhesion receptors (for example, P-selectin ), and play an important role in blood clotting.