Proteins, proteomics


Fibronectin (FN) is a high molecular weight, multidomain glycoprotein, comprising about 5% by weight of carbohydrate.

Fibronectin exhibits diverse recognition functions located on distinct fragments or domains, so FN can interact with a variety of macromolecules including/on :
extracellular matrixcollagen, 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 []


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