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  • Title: Characterization of a thrombomodulin binding site on protein C and its comparison to an activated protein C binding site for factor Va.
    Author: Gale AJ, Griffin JH.
    Journal: Proteins; 2004 Feb 15; 54(3):433-41. PubMed ID: 14747992.
    Abstract:
    Activation of the anticoagulant human plasma serine protease zymogen, protein C, by a complex of thrombin and the membrane protein, thrombomodulin, generates activated protein C, a physiologic anti-thrombotic, anti-inflammatory and anti-apoptotic agent. Alanine-scanning site-directed mutagenesis of residues in five surface loops of an extensive basic surface on protein C was used to identify residues that play essential roles in its activation by the thrombin-thrombomodulin complex. Twenty-three residues in the protein C protease domain were mutated to alanine, singly, in pairs or in triple mutation combinations, and mutants were characterized for their effectiveness as substrates of the thrombin-thrombomodulin complex. Three protein C residues, K192, R229, and R230, in two loops, were identified that provided major contributions to interactions with thrombin-thrombomodulin, while six residues, S190, K191, K217, K218, W231, and R312, in four loops, appeared to provide minor contributions. These protein C residues delineated a positively charged area on the molecule's surface that largely overlapped the previously characterized factor Va binding site on activated protein C. Thus, the extensive basic surface of protein C and activated protein C provides distinctly different, though significantly overlapping, binding sites for recognition by thrombin-thrombomodulin and factor Va.
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