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Role of the B domain for factor VIII and factor V expression and function
D D Pittman1, K A Marquette, R J Kaufman
1Genetics Institute, Cambridge, MA.
Blood
|December 15, 1994
Summary
The B domain of factor V is crucial for its thrombin activation, unlike factor VIII. Exchanging B domains improved factor VIII expression but not factor V activity.
Area of Science:
- Biochemistry
- Molecular Biology
- Hematology
Background:
- Factor V and factor VIII are homologous coagulation cofactors with similar domain structures (A1-A2-B-A3-C1-C2).
- Factor VIII expression is less efficient than factor V, mainly due to poor secretion and lower mRNA levels.
Purpose of the Study:
- To investigate the functional significance of the B domain in factor V and factor VIII.
- To determine the effect of B domain exchange on protein expression and activity.
Main Methods:
- Construction of chimeric cDNAs by exchanging the B domains of factor V and factor VIII.
- Expression of chimeric proteins in COS-1 monkey cells.
- Analysis of protein expression, secretion, and procoagulant activity.
Main Results:
- A factor VIII chimera with the factor V B domain showed enhanced expression and normal function, indicating the factor VIII B domain isn't responsible for inefficient secretion.
- A factor V chimera with the factor VIII B domain had reduced activity, suggesting the factor VIII B domain impairs factor V function.
- Factor V B domain deletion or replacement with the factor VIII B domain resulted in resistance to thrombin activation but retained Russell's viper venom (RVV) activation.
Conclusions:
- Thrombin activation of factor V requires sequences within its B domain, unlike factor VIII.
- The mechanisms of thrombin and RVV activation of factor V differ, with the B domain playing a key role in thrombin-mediated activation.