<p>Kringles are autonomous structural domains, found throughout the blood clotting and fibrinolytic proteins.Kringle domains are believed to play a role in binding mediators (e.g., membranes,other proteins or phospholipids), and in the regulation of proteolytic activity[<cite idref="PUB00002414"/>, <cite idref="PUB00001541"/>, <cite idref="PUB00003257"/>]. Kringle domains [<cite idref="PUB00003400"/>, <cite idref="PUB00000803"/>, <cite idref="PUB00001620"/>] are characterised by a triple loop, 3-disulphide bridge structure, whose conformation is defined by a number of hydrogen bonds and small pieces of anti-parallel beta-sheet. They are found in a varying number of copies in some plasma proteins including prothrombin and urokinase-type plasminogen activator, which are serine proteases belonging to MEROPS peptidase family S1A.</p><p>This entry represents a conserved site within the kringle domain that contains two of the cysteines involved in disulphide bonds.</p>