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Reversible interactions between plasminogen activators and plasminogen activator inhibitor-1.
J Mimuro1, M Kaneko, T Murakami
1Institute of Hematology, Jichi Medical School, Tochigi-Ken, Japan.
Biochimica Et Biophysica Acta
|December 28, 1992
Summary
The urokinase (UK) kringle domain has a high-affinity binding site for plasminogen activator inhibitor-1 (PAI-1), accelerating complex formation. This site, along with others in the catalytic domain, influences UK and tissue-type plasminogen activator (tPA) interactions with PAI-1.
Area of Science:
- Biochemistry
- Molecular Biology
- Protein Interactions
Background:
- Plasminogen activator inhibitor-1 (PAI-1) is a key regulator of fibrinolysis.
- Urokinase (UK) and tissue-type plasminogen activator (tPA) are serine proteases involved in clot breakdown.
- Understanding the interaction between PAs and PAI-1 is crucial for regulating thrombolytic therapy.
Purpose of the Study:
- To investigate the specific binding sites on urokinase (UK) for plasminogen activator inhibitor-1 (PAI-1).
- To elucidate the role of different UK domains in PAI-1 complex formation kinetics.
- To compare PAI-1 binding mechanisms between UK and tPA.
Main Methods:
- Peptide inhibition assays using synthetic peptides derived from UK and tPA domains.
- Analysis of complex formation rates between PAI-1 and various forms of UK and tPA.
- Use of diisopropylfluorophosphate (DFP)-inactivated enzymes to study PAI-1 binding.
Main Results:
- The UK kringle domain possesses a high-affinity PAI-1 binding site, leading to 10-fold faster complex formation with PAI-1 compared to low-molecular-weight UK (LMWUK).
- Peptides from the UK kringle and catalytic domains differentially modulated UK-PAI-1 and LMWUK-PAI-1 complex formation.
- DFP-inactivated UK and tPA inhibited PAI-1 binding to specific peptides, while single-chain UK (scuPA) did not compete.
Conclusions:
- The UK A-chain contains a reversible PAI-1 binding site critical for rapid association, comparable in importance to sites in the tPA A-chain.
- Reversible PAI-1 binding sites are exposed on UK upon conversion from scuPA, unlike in tPA.
- These findings highlight distinct mechanisms of PAI-1 regulation for UK and tPA.
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