Synthesis of Biologically Active Vitamin K-Dependent Coagulation Factors

Abstract

Several of the vitamin K-dependent proteins of blood coagulation have elicited interest as potential therapeutic agents for disorders of hemostasis or thrombosis. In particular, there has been interest in producing recombinant factor IX for treatment of hemophilia B, factor VII for treatment of hemophilia A patients with inhibitors and recombinant protein C for treatment of thrombotic disorders. Since these proteins undergo a unique posttranslational modification, the vitamin K-dependent carboxylation of specific glutamic acid residues in their amino termini to γ-carboxyglutamic acid, their expression in recombinant systems has been more difficult than that of proteins that undergo less extensive processing. A great deal of experience has been accrued on optimal expression systems and methods of growth for the vitamin K-dependent proteins. While some of these proteins are now produced on a scale that makes consideration of therapeutic use feasible, obstacles still remain to the practical production of others. For example, it remains difficult to produce fully carboxylated factor IX at high levels of expression in recombinant systems. Some of these obstacles may be surmountable with an increased understanding of the basic biological processes involved in the synthesis of the vitamin K-dependent proteins. Considerable interest has been focused on two fundamental problems: what are the factors that control the efficient γ-carboxylation of a vitamin K-dependent protein and, what effects efficient cleavage of the propeptide of a vitamin K-dependent protein? Our current understanding of the former, the process of γ-carboxylation, is the subject of this review.