| 1. |
- Maurissen, Lisbeth F A, et al.
(författare)
-
Re-evaluation of the role of the protein S-C4b binding protein complex in activated protein C-catalyzed factor Va-inactivation
- 2008
-
Ingår i: Blood. - : American Society of Hematology. - 1528-0020 .- 0006-4971. ; 111:6, s. 3034-3041
-
Tidskriftsartikel (refereegranskat)abstract
- Protein S expresses cofactor activity for activated protein C (APC) by enhancing the APC-catalyzed proteolysis at R-306 in factor Va. It is generally accepted that only free protein S is active and that complex formation with C4b-binding protein (C4BP) inhibits the APC-cofactor activity of protein S. However, the present study shows that protein S-C4BP expresses APC-cofactor activity and stimulates APC-catalyzed proteolysis at R-306 more than 10-fold, but instead inhibits proteolysis at R-506 by APC 3- to 4-fold. Free protein S stimulates APC-catalyzed cleavage at R-306 approximately 20-fold and has no effect on cleavage at R-506. The resulting net effect of protein S-C4BP complex formation on APC-catalyzed factor Va inactivation is a 6- to 8-fold reduction in factor Va inactivation when compared with free protein S, which is not explained by inhibition of APC-cofactor activity of protein S at R306, but by generation of a specific inhibitor for APC-catalyzed proteolysis at R-506 of factor Va. These results are of interest for carriers of the factor V-Leiden mutation (R(506)Q), as protein S-C4BP effectively enhances APC-catalyzed factor Va (R-306) inactivation in plasma containing factor V-Leiden.
|
|
| 2. |
|
|
| 3. |
- Segers, Kenneth, et al.
(författare)
-
Identification of surface epitopes of human coagulation factor Va that are important for interaction with activated protein C and heparin
- 2008
-
Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 283:33, s. 22573-22581
-
Tidskriftsartikel (refereegranskat)abstract
- Inactivation of factor Va (FVa) by activated protein C (APC) is a key reaction in the down- regulation of thrombin formation. FVa inactivation by APC is correlated with a loss of FXa cofactor activity as a result of three proteolytic cleavages in the FVa heavy chain at Arg(306), Arg(506), and Arg(679). Recently, we have shown that heparin specifically inhibits the APC- mediated cleavage at Arg(506) and stimulates cleavage at Arg(306). Three- dimensional molecular models of APC docked at the Arg(306) and Arg(506) cleavage sites in FVa have identified several FVa amino acids that may be important for FVa inactivation by APC in the absence and presence of heparin. Mutagenesis of Lys(320), Arg(321), and Arg(400) to Ala resulted in an increased inactivation rate by APC at Arg(306), which indicates the importance of these residues in the FVa- APC interaction. No heparin- mediated stimulation of Arg(306) cleavage was observed for these mutants, and stimulation by protein S was similar to that of wild type FVa. With this, we have now demonstrated that a cluster of basic residues in FVa comprising Lys(320), Arg(321), and Arg(400) is required for the heparin-mediated stimulation of cleavage at Arg(306) by APC. Furthermore, mutations that were introduced near the Arg(506) cleavage site had a significant but modest effect on the rate of APC- catalyzed FVa inactivation, suggesting an extended interaction surface between the FVa Arg(506) site and APC.
|
|
| 4. |
- Segers, Kenneth, et al.
(författare)
-
The role of thrombin exosites I and II in the activation of human coagulation factor V
- 2007
-
Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 282:47, s. 33915-33924
-
Tidskriftsartikel (refereegranskat)abstract
- Human blood coagulation Factor V(FV) is a plasma protein with little procoagulant activity. Limited proteolysis at Arg(709), Arg(1018), and Arg(1545) by thrombin or Factor Xa (FXa) results in the generation of activated FV, which serves as a cofactor of FXa in prothrombin activation. Both thrombin exosites I and II have been reported to be involved in FV activation, but the relative importance of these regions in the individual cleavages remains unclear. To investigate the role of each exosite in FV activation, we have used recombinant FV molecules with only one of the three activation cleavage sites available, in combination with exosite I- or II-specific aptamers. In addition, structural requirements for exosite interactions located in the B-domain of FV were probed using FV B-domain deletion mutants and comparison with FV activating enzymes from the venom of Russell's viper(RVV-V) and of Levant's viper (LVV-V) known to activate FV by specific cleavage at Arg(1545). Our results indicate that thrombin exosite II is not involved in cleavage at Arg(709) and that both thrombin exosites are important for recognition and cleavage at Arg(1545). Efficient thrombin- catalyzed FV activation requires both the N- and C-terminal regions of the B-domain, whereas only the latter is required by RVV-V and LVV-V. This indicates that proteolysis of FV by thrombin at Arg(709), Arg(1018), and Arg(1545) show different cleavage requirements with respect to interactions mediated by thrombin exosites and areas that surround the respective cleavage sites. In addition, interactions between exosite I of thrombin and FV are primarily responsible for the different cleavage site specificity as compared with activation by RVV-V or LVV-V.
|
|
