Fibronectin is a high-molecular-weight glycoprotein containing about 5% carbohydrate that binds to membrane spanning receptor proteins called integrins. In addition to integrins, they also bind extracellular matrix components such as collagen, fibrin and heparan sulfate.

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. Plasma fibronectin is made in the liver by hepatocytes. 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. Fibronectin is also found in normal human saliva, which helps prevent colonization of the oral cavity and pharynx by potentially pathogenic bacteria.