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Structural features mediating fibrin selectivity of vampire bat plasminogen activators
P Bringmann1, D Gruber, A Liese
1Research Laboratories, Schering AG Berlin, Federal Republic of Germany.
The Journal of Biological Chemistry
|October 27, 1995
Summary
Vampire bat salivary plasminogen activators (DSPAs) show a strong fibrin requirement, unlike tissue-type plasminogen activator (t-PA). This fibrin dependence is mediated by specific domains and the absence of a plasmin-sensitive site, enhancing clot lysis.
Area of Science:
- Biochemistry and Molecular Biology
- Enzymology
- Thrombosis and Hemostasis
Background:
- Plasminogen activators (PAs) are crucial for fibrinolysis, the breakdown of blood clots.
- Vampire bat salivary plasminogen activators (DSPAs) are unique PAs with a strict fibrin requirement.
- Structural comparison with urokinase (u-PA) and tissue-type plasminogen activator (t-PA) reveals conserved domains (F, E, K, P) but distinct functional properties.
Purpose of the Study:
- To elucidate the molecular mechanisms underlying the fibrin dependence and fibrin selectivity of DSPAs.
- To compare the catalytic efficiency and fibrin interaction of DSPAs with t-PA.
- To identify the structural determinants responsible for the unique fibrin cofactor requirement of DSPAs.
Main Methods:
- Biochemical characterization of four DSPA isoenzymes (DSPA α1, α2, β, γ) and t-PA.
- Plasminogen activation assays in the presence and absence of fibrin.
- Determination of catalytic efficiency (kcat/Km) and fibrin selectivity ratios.
Main Results:
- All four DSPAs exhibit significantly enhanced activity in the presence of fibrin, with DSPA α1 showing a 10^5-fold increase in catalytic efficiency.
- DSPAs demonstrate markedly higher fibrin selectivity compared to t-PA, with ratios ranging from 90 to 13,000 versus 72 for t-PA.
- Fibrin binding involves the F domain and other determinants in the K and P domains, while the absence of a plasmin-sensitive activation site contributes to fibrin dependence.
Conclusions:
- DSPAs possess a unique fibrin-binding mechanism and lack a plasmin-sensitive activation site, leading to their pronounced fibrin dependence and selectivity.
- These findings expand the understanding of fibrin-mediated plasminogen activation, highlighting the role of specific protein-protein interactions in stabilizing the active enzyme conformation.
- The structural features of DSPAs offer insights into the evolution of fibrinolytic enzymes and potential therapeutic applications.