Fibronectin, type I repeats are one of the three repeats found in the fibronectin

Fibronectin

Fibronectin is a high-molecular weight glycoprotein of the extracellular matrix that binds to membrane-spanning receptor proteins called integrins. In addition to integrins, fibronectin also binds extracellular matrix components such as collagen, fibrin and heparan sulfate proteoglycans...

 protein. Fibronectin is a plasma protein that binds cell surfaces and various compounds including collagen

Collagen

Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...

, fibrin

Fibrin

Fibrin is a fibrous, non-globular protein involved in the clotting of blood. It is a fibrillar protein that is polymerised to form a "mesh" that forms a hemostatic plug or clot over a wound site....

, heparin

Heparin

Heparin , also known as unfractionated heparin, a highly sulfated glycosaminoglycan, is widely used as an injectable anticoagulant, and has the highest negative charge density of any known biological molecule...

, DNA, and actin

Actin

Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...

. Type I domain (FN1) is approximately 40 residues in length. Four conserved cysteines are involved in disulfide bond

Disulfide bond

In chemistry, a disulfide bond is a covalent bond, usually derived by the coupling of two thiol groups. The linkage is also called an SS-bond or disulfide bridge. The overall connectivity is therefore R-S-S-R. The terminology is widely used in biochemistry...

s. The 3D structure of the FN1 domain has been determined. It consists of two antiparallel beta-sheets, first a double-stranded one, that is linked by a disulfide bond to a triple-stranded beta-sheet. The second conserved disulfide bridge links the C-terminal adjacent strands of the domain.

In human tissue plasminogen activator chain A the FN1 domain together with the following epidermal growth factor (EGF)-like domain are involved in fibrin-binding. It has been suggested that these two modules form a single structural and functional unit. The two domains keep their specific tertiary structure, but interact intimately to bury a hydrophobic core; the inter-module linker makes up the third strand of the EGF-module's major beta-sheet.

Human proteins containing this domain

F12

Factor XII

Coagulation factor XII also known as Hageman factor is a plasma protein. It is the zymogen form of factor XIIa, an enzyme of the serine protease class. In humans, factor XII is encoded by the F12 gene.- Function :...

; FN1; HGFAC

HGFAC

Hepatocyte growth factor activator is a protein that in humans is encoded by the HGFAC gene.-Further reading:...

; PLAT

Plat

A plat in the U.S. is a map, drawn to scale, showing the divisions of a piece of land. Other English-speaking countries generally call such documents a cadastral map or plan....

;