<p>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 disulphide bonds. The 3D structure of the FN1 domain has been determined [<cite idref="PUB00004065"/>, <cite idref="PUB00003289"/>, <cite idref="PUB00005265"/>]. It consists of two antiparallel beta-sheets, first a double-stranded one, that is linked by a disulphide bond to a triple-stranded beta-sheet. The second conserved disulphide bridge links the C-terminal adjacent strands of the domain.</p><p> 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 [<cite idref="PUB00002685"/>]. It has been suggested that these two modules form a single structural and functional unit [<cite idref="PUB00005265"/>]. 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.</p> Fibronectin, type I