Fibronectins Connect Cells with ECM

Fibronectins are adhesive glycoproteins present in the extracellular matrix. Their primary role is to connect cells with the matrix.

Fibronectins consist of two large subunits that are joined at their C-terminal by a couple of disulfide bonds, forming a dimer. Both the subunits contain various repeating domains that can bind to collagen fibrils, heparin of proteoglycans, and integrins - the cell-adhesion receptors. In this way, fibronectins connect cells with the matrix components.

Binding with integrin is greatly influenced by the presence of arginine, glycine, and aspartate residues, or RGD repeats, as seen in type III domains - one of the major repeating domains in fibronectins.

Once bound to fibronectin, integrins can bind to actin filaments, forming a bridge between the extracellular components and the cell's cytoskeleton. This binding transmits the tension, stretching the fibronectins and exposing their cryptic binding sites to which multiple fibronectin dimers can then bind, forming fibronectin fibrils.

These fibronectin fibrils help in epidermal cell migration and proliferation, facilitating various biological processes like wound healing.