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Amphipathic helices support function of blood coagulation factor IXa
M D Blostein1, A C Rigby, B C Furie
1Center for Hemostasis and Thrombosis Research, Beth Israel Deaconess Medical Center, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02215, USA.
Biochemistry
|September 29, 2000
Summary
A novel peptide from factor VIII enhances blood coagulation factor IXa activity by mimicking phospholipid membranes. This effect, dependent on gamma-carboxyglutamic acid domains and calcium, highlights the role of amphipathic helices in coagulation.
Area of Science:
- Biochemistry
- Molecular Biology
- Hematology
Background:
- Blood coagulation factor IXa (FXIa) activity is typically enhanced by phospholipid membranes.
- The C2 domain of factor VIII (fVIII) contains a membrane-binding peptide.
Purpose of the Study:
- To investigate the effect of a specific peptide from fVIII (fVIII(2303)(-23)) on FXIa proteolytic efficiency.
- To elucidate the mechanism and structural requirements for this enhancement.
Main Methods:
- Assays measuring FXIa proteolytic activity on factor X.
- Use of synthetic peptides, antibodies, and diastereomeric analogues to probe molecular interactions.
- Calcium ion dependency studies.
- Analysis of alpha-helical content and peptide length.
Main Results:
- fVIII(2303)(-23) significantly enhances FXIa activity in the absence of membranes by reducing the K(M) for factor X.
- This enhancement requires intact gamma-carboxyglutamic acid domains of both FXIa and factor X, and is calcium-dependent.
- Amphipathic, alpha-helical structure is critical, as demonstrated by similar effects from other helical peptides (e.g., melittin) and loss of activity with non-helical analogues or truncated peptides.
- fVIII(2303)(-23) does not provide additional enhancement when phospholipid vesicles are present.
Conclusions:
- Amphipathic helical peptides can mimic phospholipid membranes in supporting FXIa function.
- The fVIII(2303)(-23) peptide demonstrates a novel, membrane-mimetic role in blood coagulation.
- A minimum alpha-helical length is necessary for this peptide-mediated enhancement of FXIa activity.