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Measurement of Factor V Activity in Human Plasma Using a Microplate Coagulation Assay
Published on: September 9, 2012
Membrane-dependent interaction of factor Xa and prothrombin with factor Va in the prothrombinase complex
Shabir H Qureshi1, Likui Yang, Chandrashekhara Manithody
1Edward A. Doisy Department of Biochemistry and Molecular Biology, St. Louis University School of Medicine, St. Louis, Missouri 63104, USA.
Biochemistry
|April 22, 2009
Summary
Membrane phospholipids significantly enhance the prothrombinase reaction by improving factor Va binding to substrate. This interaction involves conformational changes in factor Xa, facilitating efficient thrombin generation.
Area of Science:
- Biochemistry
- Molecular Biology
- Hemostasis
Background:
- The prothrombinase complex, crucial for blood coagulation, involves factors Xa, Va, and prothrombin.
- The role of membrane phospholipids in the prothrombinase reaction remains incompletely understood despite protein-membrane interactions.
Purpose of the Study:
- To elucidate the specific role of membrane phospholipids in the prothrombinase reaction.
- To investigate how phospholipids influence the interaction between factor Va, factor Xa, and prothrombin.
Main Methods:
- Preparation of deletion derivatives of factor Xa (E2-fXa) and prothrombin (prethrombin-2).
- Analysis of catalytic activity using kinetic studies in the presence and absence of phosphatidylcholine/phosphatidylserine (PCPS) phospholipids.
- Competitive kinetic studies with exosite-1 specific ligands and direct binding assays.
Main Results:
- Phospholipids (PCPS) markedly accelerated prethrombin-2 activation by E2-fXa, with cofactor saturation observed only in phospholipid presence.
- Exosite-1 specific ligands were ineffective inhibitors in the presence of phospholipids, unlike in their absence.
- Binding studies showed phospholipids induce conformational changes in factor Xa's Gla domain, enhancing factor Va interaction.
Conclusions:
- Factor Va interaction with phospholipids is critical for enhancing the prothrombinase complex's affinity for prothrombin's exosite-1.
- Membrane phospholipids facilitate efficient thrombin generation by modulating protein-protein interactions within the prothrombinase complex.
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