Fibronectin
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Fibronectin is a high molecular weight glycoprotein containing about 5% carbohydrate that bind to receptor proteins spanning the cell membrane called integrins and to the extracellular matrix. It can also specifically bind to other molecules such as collagen, fibrin and heparin.
Fibronectin can be found in the blood plasma in its soluble form which is composed of two 250 kDa subunits joined together by disulfide bonds. The insoluble form that was formerly called cold-insoluble globulin is a large complex of cross-linked subunits.
There are several isoforms of fibronectin all of which are the product of a single gene. The structure of these isoforms are made of three types of repeated internal regions called I, II and III which exhibit different lengths and presence or absence of disulfide bonds. Alternative splicing of the Pre-mRNA leads to the combination of these three types of regions but also to a variable region.
Fibronectin is involved in the wound healing process and so can be used as a therapeutic agent. It is also one of the few proteins for which production increases with age without any associated pathology.