Site-specific functional roles of the Factor X activation peptide in the intrinsic tenase-mediated Factor X activation.

The conversion of zymogen Factor X (FX) to an active protease involves the removal of a 52-residue long activation peptide (AP). Through site-directed mutagenesis, we investigate the role of the AP and demonstrate that the high abundance of proline residues is important for efficient proteolysis of FX. Moreover, we identify an essential interaction site for Factor IXa (FIXa) between residues 22 and 30 (AP numbering) and find that the residues between 31 and 41 may provide an important interaction site for the intrinsic tenase complex, composed of Factor IXa (FIXa) and Factor VIIIa (FVIIIa).

The functional role of the autolysis loop in the regulation of factor X upon hemostatic response.

Background: The regulation of factor X (FX) is critical to maintain the balance between blood coagulation and fluidity.

Objectives: To functionally characterize the role of the FX autolysis loop in the regulation of the zymogen and active form of FX.

Methods: We introduced novel N-linked glycosylations on the surface-exposed loop spanning residues 143-150 (chymotrypsin numbering) of FX.