title: Characterization of a thrombomodulin binding site on protein C and its comparison to an activated protein C binding site for factor Va.
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.
authors.affiliation: Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, California 92037, USA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Gale
authors.forename: John H
authors.initials: JH
authors.lastname: Griffin
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D004789:Enzyme Activation / Q000187:drug effects; D015943:Factor Va / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D011486:Protein C / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits; D055672:Static Electricity; D013917:Thrombin / Q000494:pharmacology; D018180:Thrombomodulin / Q000378:metabolism*
chemical_list: D011486:Protein C; D018180:Thrombomodulin; D015943:Factor Va; D013917:Thrombin