Study of propeptide mutation effect on the human factor IX expression

Factor IX as a vitamin K-dependent blood coagulation factor requires post-translational modifications such as gamma carboxylation for its biological function. Gamma carboxylation catalyzed by an enzyme called gamma carboxylase and propeptide of vitamin K dependent proteins is first recognition site of gamma carboxylase. Specific amino acids within these propeptide sequences are responsible for differences in affinity for the gamma carboxylase. Increases of Ki result in decrease of enzyme affinity but fully gamma carboxylation of protein. Since the gamma carboxylase enzyme have least affinity for prothrombin, in this study the pMT-FIX-M13 expression vector constructed contains mutant factor IX cDNA in amino acid -13 (H to P) on the basis of prothrombin propeptide. The expression and activity of the normal and mutant recombinant factor IX were investigated by ELISA and APTT after various times of transfection. The results showed that the concentrations and activity of factor IX and so gamma carboxylation in mutant factor IX is more than healthy factor IX.