Plasminogen activation by streptokinase via a unique mechanism.
The mechanism of human plasminogen (HPlg) activation by streptokinase (SK)-type activator was investigated with recombinant truncated SK peptides. An enzyme-substrate intermediate of HPlg.SK. HPlg ternary complex was demonstrated by a sandwich-binding experiment. Formation of the ternary complex was saturable, HPlg-specific, and inhibited by 6-aminocaproic acid. Three interaction sites between SK and HPlg were demonstrated. SK-(220-414) bound to HPlg with two binding sites: one to the micro-HPlg region, the catalytic domain of HPlg, and one to the kringle 1-5 region, with Kd values of 1.50 x 10(-7) and 2.44 x 10(-6) M, respectively. SK-(16-251) bound to a single site on the kringle 1-5 region of HPlg with a Kd of 4.09 x 10(-7) M. SK-(220-414) and SK-(16-251) competed for binding on the same or nearby location on the human kringle 1-5 domain. Combination of SK-(220-414) and SK-(16-251), but not either peptide alone, could effectively activate HPlg. In addition, SK-(16-251) dose-dependently enhanced the activation of HPlg by SK-(16-414), while the HPlg activation by SK-(16-414) was inhibited by SK-(220-414). We conclude that the HPlg that binds to the COOH-terminal domains of SK functions as an enzyme to catalyze the conversion of substrate HPlg that binds to the NH2-terminal domain of SK to human plasmin.
Young
K C
KC
Department of Biochemistry, Medical College, National Cheng Kung University, Tainan, Taiwan 701, Republic of China.
Shi
G Y
GY
Wu
D H
DH
Chang
L C
LC
Chang
B I
BI
Ou
C P
CP
Wu
H L
HL
D015119:Aminocaproic Acid / Q000494:pharmacology; D001665:Binding Sites; D001667:Binding, Competitive; D006801:Humans; D018082:Kringles; D010960:Plasminogen Activators / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000494:pharmacology; D013300:Streptokinase / Q000494:pharmacology*
D011994:Recombinant Proteins; D013300:Streptokinase; D010960:Plasminogen Activators; D015119:Aminocaproic Acid