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Structural basis for reduced staphylocoagulase-mediated bovine prothrombin activation.
Rainer Friedrich1, Peter Panizzi, Shun-Ichiro Kawabata
1Proteinase Research Group, Max Planck Institute of Biochemistry, Martinsried, Germany.
The Journal of Biological Chemistry
|October 19, 2005
Summary
Staphylocoagulase (SC) activates human prothrombin (ProT) by altering its shape, but poorly activates bovine ProT due to structural differences. This species-specific activation impacts fibrinogen clotting.
Area of Science:
- Biochemistry
- Molecular Biology
- Protein Structure-Function Relationships
Background:
- Staphylocoagulase (SC) from *Staphylococcus aureus* activates human prothrombin (ProT), bypassing normal coagulation.
- SC induces a conformational change in ProT, creating a functional catalytic site without cleavage.
Purpose of the Study:
- To investigate the species specificity of SC-mediated prothrombin activation.
- To elucidate the structural basis for the differential activation of human versus bovine ProT by SC.
Main Methods:
- Biochemical assays measuring enzyme kinetics (kcat/Km, Km, kcat) for SC-ProT complexes.
- Comparative analysis of SC binding and activation of human and bovine ProT.
- Structural analysis using crystal structures of SC-thrombin complexes.
Main Results:
- SC binds human and bovine ProT with similar affinity but poorly activates bovine ProT.
- SC-bovine ProT complex exhibits significantly lower catalytic activity (kcat/Km) compared to SC-human ProT.
- Species-specific differences in ProT conformational activation by SC are primarily responsible for cofactor activity differences.
Conclusions:
- The reduced activation of bovine ProT by SC is due to incomplete catalytic site formation.
- Bovine ProT residues Arg144 and Arg145 likely hinder SC N-terminus insertion, explaining poor activation.