Crystal structures of the membrane-binding C2 domain of human coagulation factor V.
Rapid and controlled clot formation is achieved through sequential activation of circulating serine proteinase precursors on phosphatidylserine-rich procoagulant membranes of activated platelets and endothelial cells. The homologous complexes Xase and prothrombinase, each consisting of an active proteinase and a non-enzymatic cofactor, perform critical steps within this coagulation cascade. The activated cofactors VIIIa and Va, highly specific for their cognate proteinases, are each derived from precursors with the same A1-A2-B-A3-C1-C2 architecture. Membrane binding is mediated by the C2 domains of both cofactors. Here we report two crystal structures of the C2 domain of human factor Va. The conserved beta-barrel framework provides a scaffold for three protruding loops, one of which adopts markedly different conformations in the two crystal forms. We propose a mechanism of calcium-independent, stereospecific binding of factors Va and VIIIa to phospholipid membranes, on the basis of (1) immersion of hydrophobic residues at the apices of these loops in the apolar membrane core; (2) specific interactions with phosphatidylserine head groups in the groove enclosed by these loops; and (3) favourable electrostatic contacts of basic side chains with negatively charged membrane phosphate groups.
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Related Subject Headings
- Stereoisomerism
- Sequence Alignment
- Protein Structure, Tertiary
- Protein Conformation
- Protein Binding
- Molecular Sequence Data
- Models, Molecular
- Humans
- General Science & Technology
- Factor Va
Citation
Published In
DOI
ISSN
Publication Date
Volume
Issue
Start / End Page
Location
Related Subject Headings
- Stereoisomerism
- Sequence Alignment
- Protein Structure, Tertiary
- Protein Conformation
- Protein Binding
- Molecular Sequence Data
- Models, Molecular
- Humans
- General Science & Technology
- Factor Va