Structural and Functional Studies of gamma-Carboxyglutamic Acid Domains of Factor VIIa and Activated Protein C: Role of Magnesium at Physiological Calcium.

(2013) J Mol Biology 425: 1961-1981

• PubMed: 23454357 Search on PubMedSearch on PubMed Central
• DOI: https://doi.org/10.1016/j.jmb.2013.02.017
• Primary Citation of Related Structures:  
  3JTC


• PubMed Abstract: 
  

  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.

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Organizational Affiliation: 
• UCLA/Orthopaedic Hospital Department of Orthopaedic Surgery, University of California, Los Angeles, CA 90095, USA.
UCLA-DOE Institute for Genomics and Proteomics, Los Angeles, CA 90095, USA.
Division of Pulmonology and Critical Care, Department of Medicine, University of California, Los Angeles, CA 90095, USA.
Department of Hematology, The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA.
Oklahoma Medical Research Foundation, Howard Hughes Medical Institute, Oklahoma City, OK 73104, USA.
Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
UCLA/Orthopaedic Hospital Department of Orthopaedic Surgery, University of California, Los Angeles, CA 90095, USA; Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA. Electronic address: pbajaj@mednet.ucla.edu.
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