Crystal structures of Mim8 anti-FIXa and anti-FX Fab fragments in complex with their respective targets. Crystal structures of Mim8 anti-FIXa (A) and anti-FX Fab (B) fragments in complex with EGR-chloromethylketone active-site inhibited des-(Gla-EGF1) FIXa and FXa, respectively, are shown. Surface representations of the missing Gla and EGF1 domains were included based on the crystal structure of the corresponding domains from full-length human FVIIa²⁹ and with orientations obtained from a structural alignment of the respective EGF2-catalytical domains. (C) Close-up of the anti-FIXa Fab (blue cartoon representation; complementarity-determining region [CDR] loops in gray color). Neighboring residues in FIXa are shown in yellow or red as backbone stick representations with side chains included for residues 338 to 341 and 354. The relative impact of each residue on human FIX binding was evaluated by surface plasmon resonance analysis following amino acid replacement as indicated (right panel) and with the most important residues colored red. Results are shown as residual binding (mean ± standard deviation, n = 9). For all panels, the EGR-chloromethylketone inhibitor (light gray) and calcium ions (light green) are displayed as sphere representations.