Identification of individual tyrosine sulfation sites within factor VIII required for optimal activity and efficient thrombin cleavage
Factor VIII functions as an essential cofactor in the blood coagulation cascade for the factor IXa-mediated activation of factor X. Factor VIII contains 6 tyrosine residues at positions 346, 718, 719, 723, 1664, and 1680 that are modified by post-translational sulfation. This modification is require...
Saved in:
Published in | The Journal of biological chemistry Vol. 269; no. 31; pp. 20095 - 20102 |
---|---|
Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Bethesda, MD
American Society for Biochemistry and Molecular Biology
05.08.1994
|
Subjects | |
Online Access | Get full text |
Cover
Loading…
Summary: | Factor VIII functions as an essential cofactor in the blood coagulation cascade for the factor IXa-mediated activation of
factor X. Factor VIII contains 6 tyrosine residues at positions 346, 718, 719, 723, 1664, and 1680 that are modified by post-translational
sulfation. This modification is required for full factor VIII procoagulant activity. We have employed site-directed mutagenesis
to identify the individual sulfated tyrosines within factor VIII that influence activity. The molecules were expressed in
COS-1 monkey cells by transient transfection, and the resultant proteins were characterized. Metabolic incorporation of [35S]sulfate
demonstrated that all 6 tyrosine residues are sulfated in factor VIII. Sulfation at residues 346 and 1664 was required for
full activity in a factor VIII clotting assay but did not affect factor VIII activity monitored by a factor Xa generation
assay. The Tyr346-->Phe and Tyr1664-->Phe mutants displayed delayed thrombin activation that correlated with delayed cleavage
at residues 372 and 1689, respectively. In contrast, these mutants were efficiently activated by factor Xa. A triple Tyr to
Phe mutant at residues 718, 719, and 723 displayed both reduced factor VIII clotting activity and factor Xa generation activity.
Finally, a Tyr1680-->Phe mutant factor VIII displayed a 5-fold reduced affinity for von Willebrand factor. The results demonstrate
that 1) sulfation at tyrosine residues 346 and 1664 increases factor VIII activity by increasing the rate of thrombin activation
and cleavage; 2) sulfation at tyrosine residues 718, 719, and 723 increases the intrinsic activity of factor VIIIa; and 3)
sulfation at tyrosine residue 1680 increases the affinity for vWF. In addition, the results implicate that thrombin interacts
with three distinct sites within factor VIII, two of which are required for proteolytic activation. The results demonstrate
that the six sites of tyrosine sulfation modulate factor VIII activity through different mechanisms. |
---|---|
ISSN: | 0021-9258 1083-351X |
DOI: | 10.1016/S0021-9258(17)32132-4 |