Thrombin-catalyzed activation of recombinant human factor V

Area of Science:

• Biochemistry
• Molecular Biology
• Hematology

Background:

• Human factor V (FV) is a critical cofactor in the coagulation cascade.
• Proteolytic activation of FV by thrombin involves cleavage at specific sites (Arg709, Arg1018, Arg1545).
• Understanding these activation sites is key to comprehending coagulation regulation.

Purpose of the Study:

• To determine the functional significance of specific thrombin cleavage sites in human factor V activation.
• To investigate the role of Arg709, Arg1018, and Arg1545 in FV procoagulant activity.
• To compare the activation mechanisms of thrombin and Russell's viper venom (RVV-V) on FV.

Main Methods:

• Site-directed mutagenesis was used to create FV mutants with isoleucine substitutions at key thrombin cleavage sites.
• Mutant FV proteins were expressed in COS-7 cells.
• Procoagulant activity of wild-type and mutant FV was assessed following activation by thrombin or RVV-V.

Main Results:

• Thrombin cleavage at Arg709 alone did not increase FV activity.
• Cleavage at Arg709 and Arg1018 resulted in a 3.4-fold increase in FV activity.
• Maximal FV activation by thrombin required cleavage at Arg1545, which was facilitated by prior cleavage at Arg709 and Arg1018.
• RVV-V could efficiently activate FV solely through cleavage at Arg1545.
• Mutations at thrombin cleavage sites did not drastically alter FV structure, with mutants retaining partial activity.

Conclusions:

• Cleavage at Arg709 and Arg1018 is essential for thrombin-mediated maximal activation of human factor V.
• Factor V activation pathways can differ, as demonstrated by RVV-V's ability to activate FV independently of these specific thrombin sites.
• The study provides insights into the intricate regulation of the coagulation cascade through factor V activation mechanisms.