Structural snapshots of the Ixolaris-FXa complex and insights into the allosteric mechanism. (A) Top view and expansion of Ixolaris bound to FXa. Ixolaris-FXa contacts within 3Å in the HADDOCK model structure, focusing on the HBE. Residues in FXa that are in direct contact in the structure are shown in green sticks and labeled. Ixolaris residues that are in direct contact in the structure and affected in NMR experiments are shown in magenta sticks. Hydrogen bonds and salt bridges formed with the arginines and lysines in the HBE (obtained by HADDOCK output) are shown as yellow dashed lines. (B) Detail of FXa-K1 domain interface. Critical residues involved in the interface interactions are highlighted. (C) Superposition of Ixolaris/FXa (light green) binary complex with FXa apo state (blue) showing the conformation transition of the 99-loop (red), H57, D102, and R93 side chains on Ixolaris binding.