Abstract
FVIII is synthesized as a single chain precursor of approximately 280 kD with the domain structure of A1-A2-B-A3-C1-C2 and it circulates as a series of metal ion-linked heterodimers that result from cleavages at B-A3 junction as well as additional cleavages within B domain. Factor VIII is converted to its active form, factor VIIIa, upon proteolytic cleavages by thrombin and is a heterotrimer composed of the A1, A2, and A3-C1-C2 subunits. A1 subunits of factor VIIIa terminates with 36 residue segment (Met337-Arg372) rich in acidic residues. This segment is removed after cleavages at Arg336 by activated protein C, which results in inactivation of the cofactor. In the present study, site-directed mutagenesis of FVIII at Arg336 to Gln336 was performed in order to produce an inactivation resistant mutant rFVIII (rFVIIIm) with an extended physiological stability. A recombinant mutant heavy chain of FVIII (rFVIII-Hm; Arg336 to Gln336) and wild-type light chain of FVIII (rFVIII-L) were expressed in Baculovirus-insect cell (Sf9) system, and a biologically active recombinant mutant FVIII (rFVIIIm) was reconstituted from rFVIII-Hm and rFVIII-L in the FVIII-depleted human plasma containing 40 mM CaCl2. The rFVIIIm exhibited cofactor activity of FVIIIa (2.85 x 10(-2) units/mg protein) that sustained the high level activity during in vitro incubation at 37 degrees C for 24 h, while the cofactor activity of normal plasma was declined steadily for the period. These results indicate that rFVIIIm (Arg336 to Gln336) expressed in Baculovirus-insect cell system is inactivation resistant in the plasma coagulation milieu and may be useful for the treatment of hemophilia A.
Highlights
Factor VIII (FVIII) is a plasma glycoprotein cofactor that accelerates the activation of factor X by FIXa in the core reaction of blood coagulation cascade
ለThe recombinant mutant factor VIII (rFVIIIm) exhibited cofactor activity of FVIIIa (2.85 10-2 units/mg protein) that sustained the high level activity during in vitro incubation at 37 ̊C for 24 h, while the cofactor activity of normal plasma was declined steadily for the period. These results indicate that rFVIIIm (Arg336 to Gln 336) expressed in Baculovirus-insect cell system is inactivation resistant in the plasma coagulation milieu and may be useful for the treatment of hemophilia A
FVIII is synthesized as a 2,351-aa single-chain glycoprotein of 280 kDa with the domain structure of A1-A2-B-A3-C1C2 and it circulates as a series of metal ion-linked heterodimers that result from cleavages at B-A3 junction as well as additional cleavages within B domain
Summary
Factor VIII (FVIII) is a plasma glycoprotein cofactor that accelerates the activation of factor X by FIXa in the core reaction of blood coagulation cascade. Hemophilia A is an X-linked, recessive bleeding disorder (Anatonarakis et al, 1985), which affects 1 in 10,000 males, resulting in defective or deficient human clotting factor VIII molecules, necessitating exogenous replacement by either plasma- or recombinant-derived FVIII preparations. FVIII is converted to its active form, factor VIIIa, upon proteolytic cleavages by thrombin and is a heterotrimer composed of the A1, A2, and A3-C1-C2 subunits. A1 subunits of factor VIIIa terminates with 36 residue segment (Met337-Arg372) rich in acidic residues. This segment is removed after cleavages at Arg 336 by activated protein C (APC). Recent observation suggests that cleavage at Arg1719 or Arg1721 in the light chain may be unrelated to FVIII inactivation (Fay, 1993).
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