Current and previous models of EC differ regarding steric clash between FX and the anti-TF antibodies, 5G9 and 10H10. Models of EC from (A) this study and (B) Norledge et al (1NL8),²⁵ exhibiting very different binding modes of FX to TF:FVIIa. In all panels, FVIIa (orange) and sTF (cyan) are shown as ribbons, whereas FX (purple) is shown as spheres. TF residues K165 and K166 are also shown as spheres, to highlight the TF exosite. (C-D) The models from panels A-B, respectively, superimposed with the X-ray structure of sTF bound to the Fab of the inhibitory anti-TF antibody, 5G9 (PDB 1AHW),¹⁷ done by aligning the sTF components using PyMOL version 2.5.4, Schrodinger, LLC. Coloring is the same as in panels A-B, except that the sTF from 1AHW is colored magenta, and 5G9 Fab (yellow) is shown as ribbons, with side chains as sticks. In both models, significant steric clash occurs between 5G9 Fab and FX. (E-F) The models from panels A-B, respectively, superimposed with the X-ray structure of sTF bound to the Fab from the noninhibitory antibody, 10H10 (4M7L),⁷⁹ with the models rotated leftward to better view the bound 10H10 Fab. Coloring is the same as panels A-B except that the sTF from 4M7L is colored a darker blue, and 10H10 Fab (green) is shown as ribbons, with side chains as sticks. Note the lack of any steric clashes between 10H10 Fab and FX in the current model shown in panel E. In contrast, there is substantial steric clash between 10H10 Fab and FX in the Norledge et al model, shown in panel F.