Fibronectin exhibits diverse recognition functions located on distinct fragments or domains, so FN can interact with a variety of macromolecules including/on :
● extracellular matrix – collagen, glycosaminoglycans, proteoglycans, tenascin, fibulin and thrombospondin
● circulating coagulation factors – Fn is covalently incorporated into fibrin clots through the transglutaminase action of coagulation factor XIII, improving fibroblast adhesion
● fibrinolytic system
● acute phase proteins
● complement system
● cell-surface receptors on a variety of cells including fibroblasts, neurons, phagocytes and bacteria – integrins (through RGD tripeptide)
● itself, forming fibrillar entities
● small molecules such as gangliosides, sugars, and Ca ions.
Fibronectin (FN) participates in tissue repair, embryogenesis, blood clotting, and cell migration/adhesion. Cells of most tissues synthesize fibronectin. Soluble fibronectin is produced by hepatocytes and circulates, in its disulfide-bonded dimeric form, in the plasma. The soluble protomer is a compact, flexible dimer that can be converted into an insoluble, fibrillar network. The soluble-to-fibrillar conversion is a highly regulated process involving integrins and possibly other cell-surface receptors [ref] including uPAR (urokinase-type plasminogen activator receptor) [ref] and a cell-surface proteoglycan [ref].[s]
The insoluble fibronectin dimer is synthesized by fibroblasts, chondrocytes, endothelial cells, macrophages, as well as certain epithelial cells. Electron microscopic analyses of natural thin fibrils (5-18nm diameter), made by fibroblasts in culture, clearly indicate an ordered arrangement and suggest a model in which extended protomers (130nm long) are arranged end-to-end with an overlap of about 14 nm [ref]. As an extracellular adhesion molecule, FN binds to integrins and participates in wound healing.
Cell-surface receptors or fibrinogen, collagen and fibrin (as extracellular matrix proteins) facilitate the adherence of microorganisms to host tissues [ref]. The Hep-2 domain of fibronectin interacts with envelope glycoproteins on some retroviruses. Fibronectin is able to bind both the virus and cell-surface receptors, concentrating viruses on the surface of the cells, enhancing viral uptake by cells.
The structural isoforms of fibronectin arise from alternative splicing of a single gene, and possess a variable region plus three types of repeated internal regions (homologous, repeating modules I, II and III) +/- disulfide bonds.
[more]  The Type I module of fibronectin  The Type II module (F2)  segment of fibronectin , four Type III modules 
tags [Proteins] [fibronectin]