Factor V is a substrate for the transamidase factor XIIIa.

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Chemistry

Background:

• Coagulation Factor V is a key protein in the blood clotting cascade.
• Thrombin cleaves Factor V to produce the active cofactor, Factor Va.
• Factor V activation involves subunit cleavage and the generation of fragments with unknown functions.

Purpose of the Study:

• To investigate the covalent incorporation of lysine analogs into human and bovine Factor V by Factor XIIIa.
• To compare the incorporation rates and extents in activated versus unactivated Factor V.
• To identify the specific sites and fragments of Factor V involved in the transamidation reaction.

Main Methods:

• Incubation of Factor V (human and bovine, activated and unactivated) with Factor XIIIa and radiolabeled or fluorescent lysine analogs ([3H]putrescine, dansylcadaverine).
• Quantification of probe incorporation using liquid scintillation counting and fluorography.
• Identification of labeled protein fragments and polymers using polyacrylamide gel electrophoresis, immunoaffinity chromatography, and immunoprecipitation.

Main Results:

• Factor XIIIa incorporated lysine analogs into both activated and unactivated Factor V.
• Activated Factor V showed approximately twice the initial incorporation rate compared to unactivated Factor V.
• Specific fragments of human (150,000 Mr) and bovine (120,000 Mr) Factor V were identified as incorporation sites.
• Factor XIIIa mediated the formation of high molecular weight covalent polymers of Factor V.

Conclusions:

• Factor XIIIa can covalently modify Coagulation Factor V at specific sites, particularly within larger activation fragments.
• Factor V activation influences the rate of Factor XIIIa-mediated lysine analog incorporation.
• Factor XIIIa promotes the polymerization of Factor V, suggesting a potential role in coagulation complex stabilization or regulation.