Multiple inhibitory kinetics reveal an allosteric interplay among thrombin functional sites

Area of Science:

• Biochemistry
• Pharmacology
• Enzymology

Background:

• Thrombin is a critical enzyme in blood coagulation, making its inhibitors a focus of antithrombotic drug development.
• Most thrombin inhibitors are characterized by amidolytic assays, potentially overlooking effects on fibrinogen binding.

Discussion:

• An improved turbidimetric assay was employed to study the effect of various thrombin inhibitors on fibrinogen hydrolysis.
• This technique allows for efficient determination of inhibition types and kinetic constants for diverse inhibitors, including proteins, peptides, and peptidomimetics.
• The study characterized protein (recombinant hirudin, antithrombin III), peptide (bivalirudin, hirugen), and peptidomimetic (argatroban, PPACK) inhibitors for the first time regarding their inhibition types on fibrinogen hydrolysis.

Key Insights:

• The assay revealed distinct inhibition types for various thrombin inhibitors, including unexpected partial inhibition for heparin and an RNA aptamer (Toggle-25t), suggesting allosteric interactions.
• The kinetic characterization of GPRP-peptide, an inhibitor of fibrin association, was performed for the first time.
• The findings highlight a range of inhibition mechanisms and intricate allosteric interplay within thrombin.

Outlook:

• The improved turbidimetric assay is a valuable tool for studying fibrinogen hydrolysis and fibrin association inhibitors.
• The detailed kinetic characterization provides crucial insights into enzyme activity regulation.
• This research facilitates the rational design and development of novel antithrombotic agents.