Proteolytic cleavage of single-chain pro-urokinase induces conformational change which follows activation of the zymogen and reduction of its high affinity for fibrin.

Urokinase-type plasminogen activator: proenzyme, receptor, and inhibitors

“…Single-chain pro-u-PA is converted by limited proteolysis into an active Mr 50,000 enzyme consisting of two polypeptide chains held together by one disulfide bond; this conversion can be catalyzed by plasmin. Results from several laboratories have demonstrated that single-chain u-PA is a zymogen that in contrast to the two-chain active enzyme has little or no proteolytic activity against the natural substrate plasminogen, does not react with macromolecular antiproteases, lacks amidolytic activity against synthetic plasminogen activator substrates, and is unable to react with the active site titrant diisopropylfluorophosphate (2,18,26,29,39,55,64,70). It has recently been reported (33,60), however, that certain purified preparations of single-chain u-PA may also have catalytic activity; recombinant single-chain u-PA produced in Escherichia coli had a catalytic efficiency superior to that of the two-chain enzyme, and single-chain u-PA purified from different mammalian sources had variable and low, but detectable, catalytic activity.…”

“…Pig and mouse u-PA show strong homologies with the human enzyme; mouse u-PA, however, contains no N-glycosylation site (7,37). It is the single-chain form of u-PA that is released from a variety of cultured normal and neoplastic cell types (20,29,39,55,59,64,70), and that appears to be the predominant extracellular form of u-PA in the intact organism (30,54). Single-chain pro-u-PA is converted by limited proteolysis into an active Mr 50,000 enzyme consisting of two polypeptide chains held together by one disulfide bond; this conversion can be catalyzed by plasmin.…”

Longitudinal Assessment of Cytokine Expression and Plasminogen Activation in Hantavirus Cardiopulmonary Syndrome Reveals Immune Regulatory Dysfunction in End-Stage Disease

“…The uPA-uPAR system bridges the functional gap between the plasminogen activating system and inflammation by directing the migration of T cells and antigen-presenting cells, such as dendritic cells (DCs), monocytes, and macrophages, to sites of infection [ 41 , 42 , 43 , 44 , 45 ]. IFN-γ and TNF induce a plasmin-activated two-chain form of uPA [ 39 ], which binds PAI-1 with high affinity. However, IFN-γ is known to cause the tandem secretion of pro-uPA and uPAR, which then forms the pro-uPA/uPAR but binds to PAI-1 with five-fold less affinity [ 40 ] relative to the two-chain form [ 46 ].…”

“…uPA is synthesized as a single-chain zymogen (scuPA), also known as pro-uPA [38], and activated upon binding to urokinase-type plasminogen activator receptor (uPAR). Activated pro-uPA cleaves the zymogen plasminogen to produce the protease plasmin, converting pro-uPA to its active two-chain form [39]. PAI-1 efficiently inhibits uPA activity in plasma and most tissues by binding to both free uPA and uPAR-bound active uPA but poorly interacts with the pro-uPA-uPAR complex [40][41][42][43][44].…”

“…IFN-γ and TNF induce a plasmin-activated two-chain form of uPA [39], which binds PAI-1 with high affinity. However, IFN-γ is known to cause the tandem secretion of pro-uPA and uPAR, which then forms the pro-uPA/uPAR but binds to PAI-1 with five-fold less affinity [40] relative to the two-chain form [46].…”