Fibronectin type I domain

Fibronectin, type I repeats are one of the three repeats found in the fibronectin protein. Fibronectin is a plasma protein that binds cell surfaces and various compounds including collagen, fibrin, heparin, DNA, and actin. Type I domain (FN1) is approximately 40 residues in length. Four conserved cysteines are involved in disulfide bonds. The 3D structure of the FN1 domain has been determined.^[1][2][3] 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.^[4] It has been suggested that these two modules form a single structural and functional unit.^[3] 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.