Blood clotting reactions, such as those catalyzed by the tissue factor: factor VIIa complex (TF:
FVIIa), assemble on membrane surfaces containing anionic phospholipids such as
phosphatidylserine (PS). In fact, membrane binding is critical for the function of most of the
steps in the blood clotting cascade. In spite of this, our understanding of how the membrane
contributes to catalysis, or even how these proteins interact with phospholipids, is
incomplete. Making matters more complicated, membranes containing mixtures of PS and …