Key protein-protein interactions between the TF/FVIIa complex and the FX light chain portion of XK1. (A) The TF/FVIIa/XK1 cryo-EM density map, together with the atomic model, is repeated here from Figure 3A for orientation purposes. Color scheme: FVIIa, orange; TF, purple; and XK1, light sea green. (B) Close-up view of the interaction between TF residue R200 and FX residue E51 (in the EGF1 domain of XK1), shown with (left) and without (right) the cryo-EM density map. (C) Close-up view of the GLA domains of FVIIa and XK1 in proximity to the TF 4×Ser loop (indicated by purple arrow), shown with (left) and without (right) the cryo-EM density map. (D) Another close-up view highlighting interactions between the two GLA domains, and between the GLA domains and TF, shown with and without the density map. Interactions between TF residue K165, FVIIa residues γ35 and R36, and XK1 residue K45 are highlighted. (E) A close-up view (from a different angle relative to panels C-D), revealing interactions between the XK1 GLA domain and the TF exosite, shown with (left) and without (right) the cryo-EM density map. Interactions between XK1 residues γ14 and γ19 with TF residues K159, K166, and Y185 are highlighted.