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Related Experiment Videos

Intermolecular interactions between protein C inhibitor and coagulation proteases

S T Cooper1, H C Whinna, T P Jackson

  • 1Department of Pathology, University of North Carolina School of Medicine, Chapel Hill 27599-7035, USA.

Biochemistry
|October 10, 1995
PubMed
Summary

Protein C inhibitor (PCI) mutations reveal key residues for protease specificity. Specific substitutions enhance inhibition of thrombin, activated protein C (APC), and factor Xa by altering interactions within the reactive site loop.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Structural Biology

Background:

  • Protein C inhibitor (PCI) is a crucial plasma serine protease inhibitor.
  • Understanding PCI's specificity is vital for elucidating serpin-protease interactions.
  • Previous studies lacked detailed residue-specific insights into PCI's broad inhibitory activity.

Purpose of the Study:

  • To identify specific residues in the PCI reactive site loop that dictate its inhibition specificity.
  • To investigate the molecular interactions governing PCI's kinetics with thrombin, activated protein C (APC), and factor Xa.
  • To correlate mutational effects with structural insights derived from molecular modeling.

Main Methods:

  • Generated 19 mutations within the PCI reactive site loop (Thr352 to Arg357).

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  • Assayed inhibitory activity of mutant PCI against thrombin, APC, and factor Xa.
  • Constructed a molecular model of PCI and performed docking simulations with target proteases.

    • Main Results:

    • Mutations at the P2 position (Phe353) with Pro or Gly significantly enhanced thrombin inhibition (2- and 7-fold increases).
    • Substitutions at the P3 position (Thr352) with Arg increased inhibition rates for APC (2-fold) and factor Xa (5-fold).
    • Molecular modeling predicted specific interactions, such as salt bridges, explaining the observed kinetic changes.

    Conclusions:

    • Specific residues in the PCI reactive site loop, particularly at P2 and P3 positions, are critical for protease specificity.
    • Mutations altering steric hindrance and forming new interactions (e.g., salt bridges) modulate inhibitory potency.
    • PCI serves as a valuable model system for studying serpin-protease interactions through combined mutagenesis and molecular modeling.