Effects of Introducing Fibrinogen Aα Character into the Factor XIII Activation Peptide Segment

摘要

The formation of a blood clot involves the interplay of thrombin, fibrinogen, and Factor XIII. Thrombin cleaves fibrinopeptides A and B from the N-termini of the fibrinogen Aα and Bβ chains. Fibrin monomers are generated that then polymerize into a noncovalently associated network. By hydrolyzing the Factor XIII activation peptide segment at the R37-G38 peptide bond, thrombin assists in activating the transglutaminase FXIIIa that incorporates cross links into the fibrin clot. In the current research, the kinetic effects of introducing fibrinogen Aα character into the FXIII AP segment were examined. About 25% of fibrinogen Aα is phosphorylated at Ser 3 producing a segment with improved binding to thrombin. FXIII AP (²²AEDDL²⁶) has sequence properties in common with Fbg Aα (¹ADSpGE⁵). Kinetic benefits to FXIII AP cleavage were explored by extending FXIII AP (28–41) to FXIII AP (22–41) and examining peptides with D24, D24S, D24Sp, and D24Sp P27G. These modifications did not provide the same kinetic advantages as observed with Fbg Aα (1–20) S3p. Such results further emphasize that FXIII AP derives most of its substrate specificity from the P9-P1 segment. To enhance the kinetic properties of FXIII AP (28–41), substitutions were introduced at the P9, P4, and P3 positions. Studies reveal that FXIII AP (28–41) V29F, V34G, V35G exhibits kinetic improvements that are comparable to FXIII AP V29F, V34L and approach those of Fbg Aα (7–20). Selective changes to the FXIII AP segment sequence may be used to design FXIII species that can be activated more or less readily.