1QRZ

Human Plasminogen is a serine protease, a member of the Trypsin superfamily. It is a zymogen that can be activated to give the serine protease plasmin. Plasmin hydrolyses fibrin and dissolves blood clots. Plasmin has broad specificity but preferentially cleaves Lys-Xaa to Arg-Xaa amide bonds and can not directly catalyse proteolytic activation of plasminogen - it activates activators instead.

Under physiological conditions, activation is mediated by limited proteolysis carried out by urokinase and tissue-type plasminogen activator.

Like most zymogens, plasminogen has an activation loop which is proteolytically cleaved between Arg 561 and Val 562 when the protein is activated, resulting in conformational changes, including formation of a new solvent-inaccessible salt bridge and a functional active site.

Plasminogen activation is known to play a role in the activation of metalloproteinases and lipoxygenase and is linked to many physiological and pathological processes involved in cell migration such as cancer metastasis, angiogenesis, ovum maturation, embryogenesis, wound healing and pathogen invasion.

The PDB code 1qrz refers to the inactive precursor plasminogen, which is activated by cleavage leading to the opening of the active site. The specificity pocket is similar to that of trypsin, with plasmin showing a preference for cleavage after aliphatic basic residues such as Lysine and Arginine.