Interaction between FVIIa and FX protease domains in the model primarily involves the substrate-binding pocket of FVIIa. All snapshots were taken at the end of the equilibrium simulations (totaling 550 nanoseconds). FX is shown in purple, and FVIIa in orange. Key residues are illustrated as sticks, labeled and colored according to their respective molecules. The corresponding chymotrypsinogen numbering for critical residues is provided in black with an asterisk (∗). The catalytic triad residues H193, D242, and S344 (H57, D102, and S195 in chymotrypsinogen numbering) are emphasized in bold. Carbon atoms follow their respective molecule color schemes, while oxygen is red, nitrogen is blue, and hydrogen is white. (A) Close-up view of the FVIIa protease domain with the P1 residue of FX (R194) docked into the primary specificity pocket of FVIIa, comprising residues D338, G265, and G275 (corresponding to D189, G216, and G226 in chymotrypsinogen numbering).^71-73 Because residues G265 and G275 lack side chains, the backbone of FVIIa at these locations was colored in gray. (B) A 90° rotated view of the specificity pocket in FVIIa, focusing on the 140s loop in FVIIa (residues W284-A294 and W142-A152 in chymotrypsinogen numbering, highlighted in yellow).