In-depth structure-function profiling of the complex formation between clotting factor VIII and heme.

Area of Science:

• Biochemistry
• Molecular Biology
• Hematology

Background:

• Intravascular hemolysis, common in blood disorders like sickle cell disease, leads to heme accumulation.
• Heme accumulation can trigger pro-inflammatory and pro-thrombotic responses, affecting blood coagulation.
• Previous studies showed heme binding to coagulation factors like FVIII, fibrinogen, and activated protein C.

Purpose of the Study:

• To characterize the molecular interactions between factor VIII (FVIII) and heme.
• To investigate the physiological relevance of the FVIII-heme complex in blood coagulation.

Main Methods:

• Utilized biochemical, biophysical, structural biology, and bioinformatic tools.
• Employed heme binding assays with FVIII-derived peptides.
• Applied molecular docking, dynamic simulations, and cryo-electron microscopy.

Main Results:

• Factor VIII (FVIII) exhibits high heme-binding capacity, accommodating up to seven heme molecules.
• Identified three high-affinity and four moderate heme-binding motifs (HBMs) on FVIII.
• Demonstrated approximately 50% inhibition of FVIII cofactor activity upon heme complex formation in plasma.

Conclusions:

• Novel molecular insights into FVIII-heme interaction and its physiological impact.
• Heme binding to FVIII reduces intrinsic pathway activity and enhances final clotting steps in hemolytic conditions.
• Findings suggest implications for FVIII substitution therapy in hemophilia A patients during hemolytic events.