Structural and Functional Studies of γ-Carboxyglutamic Acid Domains of Factor VIIa and Activated Protein C: Role of Magnesium at Physiological Calcium
| Autor: | S. Paul Bajaj, Sayeh Agah, Kanagasabai Vadivel, Madhu S. Bajaj, Kaillathe Padmanabhan, Duilio Cascio, Charles T. Esmon, Sriram Krishnaswamy, Amanda S. Messer |
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| Rok vydání: | 2013 |
| Předmět: |
Models
Molecular inorganic chemicals Conformational change Protein Conformation Protein Data Bank (RCSB PDB) Factor VIIa Crystallography X-Ray Article chemistry.chemical_compound Tissue factor Structural Biology medicine Humans Magnesium Molecular Biology Phospholipids Gla domain Endothelial protein C receptor Binding Sites Chemistry Biochemistry Biophysics Carboxyglutamic acid Phospholipid Binding Calcium 1-Carboxyglutamic Acid Protein C Protein Binding medicine.drug |
| Zdroj: | Journal of Molecular Biology. 425:1961-1981 |
| ISSN: | 0022-2836 |
| Popis: | Crystal structures of factor (F) VIIa/soluble tissue factor (TF), obtained under high Mg(2+) (50mM Mg(2+)/5mM Ca(2+)), have three of seven Ca(2+) sites in the γ-carboxyglutamic acid (Gla) domain replaced by Mg(2+) at positions 1, 4, and 7. We now report structures under low Mg(2+) (2.5mM Mg(2+)/5mM Ca(2+)) as well as under high Ca(2+) (5mM Mg(2+)/45 mM Ca(2+)). Under low Mg(2+), four Ca(2+) and three Mg(2+) occupy the same positions as in high-Mg(2+) structures. Conversely, under low Mg(2+), reexamination of the structure of Gla domain of activated Protein C (APC) complexed with soluble endothelial Protein C receptor (sEPCR) has position 4 occupied by Ca(2+) and positions 1 and 7 by Mg(2+). Nonetheless, in direct binding experiments, Mg(2+) replaced three Ca(2+) sites in the unliganded Protein C or APC. Further, the high-Ca(2+) condition was necessary to replace Mg4 in the FVIIa/soluble TF structure. In biological studies, Mg(2+) enhanced phospholipid binding to FVIIa and APC at physiological Ca(2+). Additionally, Mg(2+) potentiated phospholipid-dependent activations of FIX and FX by FVIIa/TF and inactivation of activated factor V by APC. Since APC and FVIIa bind to sEPCR involving similar interactions, we conclude that under the low-Mg(2+) condition, sEPCR binding to APC-Gla (or FVIIa-Gla) replaces Mg4 by Ca4 with an attendant conformational change in the Gla domain ω-loop. Moreover, since phospholipid and sEPCR bind to FVIIa or APC via the ω-loop, we predict that phospholipid binding also induces the functional Ca4 conformation in this loop. Cumulatively, the data illustrate that Mg(2+) and Ca(2+) act in concert to promote coagulation and anticoagulation. |
| Databáze: | OpenAIRE |
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