Cancer Institute A national cancer institute
designated cancer center

Lawrence Leung

Publication Details

  • Thrombin activation of factor XI on activated platelets requires the interaction of factor XI and platelet glycoprotein Ib alpha with thrombin anion-binding exosites I and II, respectively (Retracted Article. See vol 282, pg 29067, 2007) JOURNAL OF BIOLOGICAL CHEMISTRY Yun, T. H., Baglia, F. A., Myles, T., Navaneetham, D., Lopez, J. A., Walsh, P. N., Leung, L. L. 2003; 278 (48): 48112-48119


    Activation of factor XI (FXI) by thrombin on stimulated platelets plays a physiological role in hemostasis, providing additional thrombin generation required in cases of severe hemostatic challenge. Using a collection of 53 thrombin mutants, we identified 16 mutants with <50% of the wild-type thrombin FXI-activating activity in the presence of dextran sulfate. These mutants mapped to anion-binding exosite (ABE) I, ABE-II, the Na+-binding site, and the 50-insertion loop. Only the ABE-II mutants showed reduced binding to dextran sulfate-linked agarose. Selected thrombin mutants in ABE-I (R68A, R70A, and R73A), ABE-II (R98A, R245A, and K248A), the 50-insertion loop (W50A), and the Na+-binding site (E229A and R233A) with <10% of the wild-type activity also showed a markedly reduced ability to activate FXI in the presence of stimulated platelets. The ABE-I, 50-insertion loop, and Na+-binding site mutants had impaired binding to FXI, but normal binding to glycocalicin, the soluble form of glycoprotein Ibalpha (GPIb alpha). In contrast, the ABE-II mutants were defective in binding to glycocalicin, but displayed normal binding to FXI. Our data support a quaternary complex model of thrombin activation of FXI on stimulated platelets. Thrombin bound to one GPIb alpha molecule, via ABE-II on its posterior surface, is properly oriented for its activation of FXI bound to a neighboring GPI alpha molecule, via ABE-I on its anterior surface. GPIb alpha plays a critical role in the co-localization of thrombin and FXI and the resultant efficient activation of FXI.

    View details for DOI 10.1074/jbc.M306925200

    View details for Web of Science ID 000186731400092

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