Structural alignment of the ABE I regions of Prothrombin (4HZH), thrombin-PAR3 (2PUX), and PPACK-thrombin (1PPB). Regions encompassing exosite I (residues F34-M84, thrombin straight numbering) were selected and then a backbone alignment was performed using MolMol. The backbone ABE I RMSD values for the different protein-protein comparisons were then determined: ProT and thrombin-PAR3 0.79 A, PPACK-thrombin and thrombin-PAR3 0.47A, ProT and PPACK-thrombin 0.63 Å. This analysis reveals no striking differences for the backbone atoms located in ABE I.