Engineered recombinant factor VII Q217 variants with altered inhibitor specificities.

Area of Science:

• Biochemistry
• Molecular Biology
• Hematology

Background:

• Recombinant factor VII (rFVII) is a crucial hemostatic agent.
• Understanding the structure-function relationship of FVII is vital for developing improved therapeutics.
• Residue 217 plays a role in the catalytic activity and regulatory interactions of FVII.

Purpose of the Study:

• To characterize recombinant factor VII variants with mutations at residue 217 (Q217A, Q217E, Q217G).
• To investigate the impact of these mutations on clotting activity, substrate activation, and inhibitor interactions.
• To elucidate the role of residue 217 in regulating factor VIIa (FVIIa) function.

Main Methods:

• Site-directed mutagenesis to create FVII variants (VIIQ217A, VIIQ217E, VIIQ217G).
• Prothrombin time (PT) assays to assess clotting activity.
• Enzyme kinetics (kcat/KM) for factor X activation.
• Chromogenic substrate assays.
• Inhibition assays with tissue factor pathway inhibitor (TFPI) and antithrombin III (ATIII).

Main Results:

• VIIQ217E exhibited 100% clotting activity, while VIIQ217A and VIIQ217G showed 15% and <1% activity, respectively.
• All variants were activated by factor Xa; autoactivation with tissue factor (TF) was efficient for VIIQ217E but reduced for VIIQ217A and absent for VIIQ217G.
• VIIaQ217E showed a 10-fold higher kcat for chromogenic substrate cleavage, while VIIaQ217A demonstrated altered interactions with TFPI and ATIII.

Conclusions:

• Residue 217 is critical for regulating the catalytic activity of factor VIIa (FVIIa).
• Mutations at Q217 significantly impact substrate activation and interactions with key inhibitors like TFPI and ATIII.
• These findings provide insights into the molecular mechanisms governing FVIIa function and inhibitor recognition.