Qualitative defects observed for patients with hemophilia B with variants at residues coordinating calcium ions in the Gla and EGF-1 domains. (A) Hemophilia B cases harboring an amino acid substitution variant in the Gla, EGF-1, or EGF-2 domain classified by disease severity and evaluated for their residual FIX:Ag level in the plasma. (B) FIX:Ag/FIX:Act determined per case and grouped per unique variant in the Gla domain. Dots represent the individual case values, bars represent median values per unique variant, and residues involved in calcium coordination are marked by asterisks. (C) FIX:Ag/FIX:Act determined per case and grouped per unique variant in the EGF-1 and EGF-2 domains. (D) Zymogen FIX model with incorporation of the EGF-1 crystal structure.23 Visualization in PyMOL with colors representing functional domains and calcium ion coordination residues in the EGF-1 is in orange. (E) Graphical overview of calcium ion coordinating residues in the EGF-1 domain. (F) Amino acid sequence homology of EGF-1 domain between FIX, FVII, and FX (National Center for Biotechnology Information basic local alignment search tool EGF-1 FIX; Homo sapiens) with residues in the consensus sequence indicated by an asterisk. All hemophilia B case data are based on the EAHAD F9 Variant Database (accessed on 6 May 2024).
