The role of fragment X polymers in the fibrin enhancement of tissue plasminogen activator-catalyzed plasmin formation.
When thrombin-mediated fibrin formation and tissue plasminogen activator (t-PA)-mediated fibrinolysis proceed in dynamic interaction, desA-(desB beta 1-42)-fragment X polymers are shown to be the predominant fibrin derivatives present during the rapid second phase of Glu1- and Lys78-plasminogen activation. To further investigate the effect of this intermediate, a method was developed for the production and purification of fibrinogen-derived desA-(desB beta 1-42)-fragment X, deprived of both COOH-terminal A alpha-chains, but still capable of thrombin-mediated polymerization. DesA-(desB beta 1-42)-fragment X polymer was compared to intact fibrin with regard to its stimulatory effect on Glu1-, Lys78-, and Val443-plasminogen activation, and its binding of Glu1- and Lys78-plasminogen. Pure fragment X polymer gave rise to a biphasic activation pattern like that of fibrin, demonstrating similar kinetics of rapid phase activation. The dissociation constant for the binding of plasminogen to the effector decreases by a factor of 14, and the stoichiometry increases by a factor of 2 upon plasmin-catalyzed cleavage of both native Glu1- to Lys78-plasminogen, and fibrin to fragment X polymer. We conclude that desA-fibrin protofibril formation is sufficient to initiate fibrin enhancement of t-PA-catalyzed plasminogen activation, and that optimal stimulation depends on further plasmin-mediated modification of the fibrin effector to desA-fragment X-related moieties. Optimal stimulation is dependent on the presence of the kringle 1-4 domains of plasminogen and probably results from altered and increased binding of both plasminogen and t-PA to the modified effector.
Suenson
E
E
Department of Clinical Chemistry, Rigshospitalet, University of Copenhagen, Denmark.
Bjerrum
P
P
Holm
A
A
Lind
B
B
Meldal
M
M
Selmer
J
J
Petersen
L C
LC
D000595:Amino Acid Sequence; D005337:Fibrin / Q000378:metabolism*; D005338:Fibrin Fibrinogen Degradation Products / Q000378:metabolism*; D005341:Fibrinolysin / Q000378:metabolism*; D005342:Fibrinolysis; D007700:Kinetics; D008969:Molecular Sequence Data; D010959:Tissue Plasminogen Activator / Q000378:metabolism*
D005338:Fibrin Fibrinogen Degradation Products; C030568:fibrinogen fragment X; D005337:Fibrin; D010959:Tissue Plasminogen Activator; D005341:Fibrinolysin