Substitution of the Gla domain in factor X with that of protein C impairs its interaction with factor VIIa/tissue factor: lack of comparable effect by similar substitution in factor IX.
We previously reported that the first epidermal growth factor-like (EGF1) domain in factor X (FX) or factor IX (FIX) plays an important role in the factor VIIa/tissue factor (FVIIa/TF)-induced coagulation. To assess the role of gamma-carboxyglutamic acid (Gla) domains of FX and FIX in FVIIa/TF induced coagulation, we studied four new and two previously described replacement mutants: FX(PCGla) and FIX(PCGla) (Gla domain replaced with that of protein C), FX(PCEGF1) and FIX(PCEGF1) (EGF1 domain replaced with that of protein C), as well as FX(PCGla/EGF1) and FIX(PCGla/EGF1) (both Gla and EGF1 domains replaced with those of protein C). FVIIa/TF activation of each FX mutant and the corresponding reciprocal activation of FVII/TF by each FXa mutant were impaired. In contrast, FVIIa/TF activation of FIX(PCGla) was minimally affected, and the reciprocal activation of FVII/TF by FIXa(PCGla) was normal; however, both reactions were impaired for the FIX(PCEGF1) and FIX(PCGla/EGF1) mutants. Predictably, FXIa activation of FIX(PCEGF1) was normal, whereas it was impaired for the FIX(PCGla) and FIX(PCGla/EGF1) mutants. Molecular models reveal that alternate interactions exist for the Gla domain of protein C such that it is comparable with FIX but not FX in its binding to FVIIa/TF. Further, additional interactions exist for the EGF1 domain of FX, which are not possible for FIX. Importantly, a seven-residue insertion in the EGF1 domain of protein C prevents its interaction with FVIIa/TF. Cumulatively, our data provide a molecular framework demonstrating that the Gla and EGF1 domains of FX interact more strongly with FVIIa/TF than the corresponding domains in FIX.
Ndonwi
Matthew
M
Department of Pharmacological and Physiological Sciences, Saint Louis University School of Medicine, Saint Louis, Missouri 63104, USA.
Broze
George J
GJ
Agah
Sayeh
S
Schmidt
Amy E
AE
Bajaj
S Paul
SP
D000818:Animals; D005164:Factor IX / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015942:Factor VIIa / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D005170:Factor X / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D011485:Protein Binding / Q000235:genetics; D011486:Protein C / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013925:Thromboplastin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D011486:Protein C; D011993:Recombinant Fusion Proteins; D005164:Factor IX; D005170:Factor X; D013925:Thromboplastin; D015942:Factor VIIa