TFPI isoform structures. Shown are the amino acid structures of TFPIα and TFPIβ. Each small circle represents an individual amino acid. Small red circles indicate the residues in K1 and K2 which bind the active sites of FVIIa and FXa, respectively; small purple circles, residues in K3 which bind protein S; small blue and orange circles, the conserved basic and hydrophobic residues, respectively, which bind the acidic region of FVa. The domains required for inhibition of TF/FVIIa, FXa, and prothrombinase (FXa/FVa) are indicated by shaded red, blue, and yellow ovals, respectively. TFPIβ is anchored to the membrane through a GPI anchor (green hexagons).