EPCR structure. The soluble EPCR molecule (yellow ribbon) with a portion of the protein C Gla domain (green ribbon), and a lipid molecule (the space filling balls in the center). In EPCR, 2 α-helices and an 8-strand β-sheet create a groove that is filled with the phospholipid. Binding of calcium ions (magenta spheres) to the protein C Gla domain exposes the N-terminal ω-loop to interact with EPCR (reproduced from Oganesyan et al., J Biol Chem. 2002;277:24851-24854).³