Functional and Molecular Characterization of C91S Mutation in the Second Epidermal Growth Factor-like Domain of Factor VII

Coagulation Factor VII is a vitamin K-dependent serine protease which has a pivotal role in the initiation of the coagulation cascade. The congenital Factor VII deficiency is a recessive hemorrhagic disorder that occurs due to mutations of F7 gene. In the present study C91S (p.C91S) substitution was detected in a patient with FVII deficiency. This mutation has not been characterized by a functional study.
In this study, we aimed to evaluate the impact of C91S substitution on factor VII expression and function.
The F7 complete cDNA was isolated from HepG2 cell line and inserted into the pcDNA3.1 mammalian expression vector. The desired mutation was generated by the site-directed mutagenesis and the wild-type and mutated constructs were transfected into CHO-K1 cells. The protein activity and antigen level (antigen concentration) were validated in the culture medium and cell lysate of the transiently transformed cells. An immunocytochemistry procedure was also performed to evaluate the intracellular localization of the mutated and the wild-type FVII, as well.
The present in vitro study has demonstrated that C91S antigen expression was increased in the transfected CHO-K1 cells compared to the wild-type (WT) protein. Despite an increased protein secretion, the factor VII coagulant activity was diminished following C91S substitution when it was assessed by a standard one-stage analysis. In addition, the immunocytochemistry procedure revealed that there was no difference in the intracellular localization of the C91S mutated FVII compared to the WT protein.
Our results present that C91S mutation has an effect on the coagulation activity, secretion, biosynthesis, and probably folding of the FVII leading to the FVII deficiency.