Gly222Asp and Ser379Lys — Novel Factor X Gene Mutations in severe FX Deficiency — Greifswald Registry of Factor X congenital Deficiency

Abstract

Factor X (FX) is a vitamin K-dependent plasma protein which plays a central role in blood coagulation. It is activated into the serine protease factor Xa (FXa) either by the intrinsic tenase complex (factor IXa/factor Villa) or by the tissue factor (extrinsic) pathway. FXa, in complex with its cofactor factor Va, forms the prothrombinase complex and is the important physiological activator of prothrombin. In the liver the 488-amino acid FX precursor is synthesized. Before secretion, the precursor undergoes several post-translational modifications. These steps include removal of the 40-amino acid pre-pro leader sequence (-40 to -1 ), γ-carboxylation of the first 11 glutamin acid residues, β-hydroxylation of Asp63, and excision of the Arg 140-Lys-Arg tripeptide. The resulting two chain zymogen consists of a 139-amino acid light-chain linked to a 306-amino acid heavy-chain by a single disulphide bond between Cys l32 and Cys302. The light-chain includes the amino-terminal γ-carboxy-glutamic acid (Gla) domain that contains the 11 Gla residues. A short helical stack is present downstream of the Gla domain, followed by two consecutive epidermal growth factor like domains (EGF1 and EGF2). The amino terminus of the heavy-chain includes a 52-amino acid activation peptide, followed by the protease domain which contains the active site triade of His236, Asp282, and Ser379 typical of serine proteases [1].