Localization of functionally important epitopes within the second C-type domain of coagulation factor V using...

Area of Science:

• Biochemistry
• Molecular Biology
• Hematology

Background:

• Coagulation factor V is crucial for the prothrombinase complex.
• Its C-type domains are homologous to factor VIII and other proteins.
• The second C-type domain (C2) is vital for procoagulant activity and phosphatidylserine binding.

Purpose of the Study:

• To investigate the functional roles of the C2 domain of coagulation factor V.
• To determine how substitutions with homologous regions from factor VIII or BA46 affect activity.
• To map specific functional sites within the C2 domain.

Main Methods:

• Construction and analysis of chimeric factor V proteins with domain substitutions.
• Assays to measure procoagulant activity and phosphatidylserine binding.
• Antibody binding studies to probe protein function.

Main Results:

• Full substitution of the C2 domain with heterologous domains did not restore significant activity.
• Partial, exon-size substitutions yielded chimeric proteins with partial procoagulant activity (~10% of factor Va).
• The amino-terminal region of C2 is essential for phosphatidylserine binding.
• A distinct site in the central C2 region is involved in a separate function critical for activity.
• The carboxyl-terminal region of C2 contains the molecular basis for the light chain doublet.

Conclusions:

• The C2 domain of factor V has distinct functional regions.
• Specific substitutions can partially restore function, highlighting the importance of domain structure.
• The amino-terminal, central, and carboxyl-terminal regions of C2 play specific roles in factor V function and regulation.