Clotting Cascade

Tissue factor starts a cascade of interactions that lead to formation of a clot. The first step occurs when factor VII, which is found in the blood, binds to tissue factor. When it binds to tissue factor, as shown in PDB structure 1dan, it becomes almost a thousand times more active. It can then make a specific cut in factor X (shown here from PDB entries 1xka and 1iod), changing it into an active form. Factor X then activates thrombin, which then creates the fibrin that forms the fibrous structure of the clot. The trick to this cascading process is that a few molecules of tissue factor and factor VII can activate many copies of factor X, which can activate even more thrombin, which finally activates lots and lots of fibrin.