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Factor XII Structure-Function Relationships.

Aleksandr Shamanaev1, Maxim Litvak1, Ivan Ivanov1

  • 1Department of Pathology, Microbiology and Immunology, Vanderbilt University Medical Center, Nashville, Tennessee.

Seminars in Thrombosis and Hemostasis
|June 5, 2023
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Summary
This summary is machine-generated.

Factor XII (FXII) circulates in a closed, inactive form, but surface binding via its EGF1 domain opens it for activation. This impacts angioedema and thrombosis, offering new therapeutic targets.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Hemostasis and Thrombosis

Background:

  • Factor XII (FXII) is a zymogen protease involved in angioedema and thrombosis.
  • FXII activation and activity increase upon surface binding.
  • FXII shares homology with pro-hepatocyte growth factor activator (pro-HGFA).

Purpose of the Study:

  • To investigate the structural and enzymological basis of FXII activation and its role in pathology.
  • To elucidate the mechanism by which surface binding enhances FXII activity.
  • To explore the implications for treating FXII-related disorders.

Main Methods:

  • Structural and enzymological analysis of FXII.
  • Creation and testing of FXII-pro-HGFA domain-swapped variants.
  • Assays for FXII activation and activity in fluid and surface-bound states.

Main Results:

  • FXII heavy chain normally restricts reciprocal activation with prekallikrein.
  • Pro-HGFA replacements in FXII domains 2 or kringle accelerate activation, disrupting heavy chain regulation.
  • Loss of surface-enhanced activation when FXII EGF1 domain is replaced with pro-HGFA EGF1.
  • FXII exists in a closed, inactive form stabilized by intramolecular interactions.

Conclusions:

  • FXII's closed conformation, maintained by fibronectin type 2 and kringle domains, resists activation.
  • Surface binding via the EGF1 domain disrupts these interactions, leading to an open, activatable conformation.
  • Understanding this mechanism is crucial for developing treatments for hereditary angioedema and thrombosis.