title: Human protein S cleavage and inactivation by coagulation factor Xa.
abstract: Human factor Xa specifically cleaves the anticoagulant protein S within the thrombin-sensitive domain. Amino-terminal amino acid sequencing of the heavy chain cleavage product indicates cleavage of protein S by factor Xa at Arg60, a site that is distinct from those utilized by alpha-thrombin. Cleavage by factor Xa is unaffected by the presence of hirudin and is completely blocked by tick-anticoagulant-peptide and D-Glu-Gly-Arg-chloromethyl ketone, the latter two being specific inhibitors of factor Xa. The cleavage requires the presence of phospholipid and Ca2+, and is markedly inhibited by the presence of factor Va. Factor Xa-cleaved protein S no longer possesses its activated protein C-dependent or -independent anticoagulant activity, as measured in a factor VIII-based activated partial thromboplastin time clot assay. The apparent binding constant for protein S binding to phospholipid (Kd approximately 4 nM +/- 1.0) is unaffected by factor Xa or thrombin cleavage, suggesting that the loss of anticoagulant activity resulting from cleavage is not primarily due to the loss of membrane binding ability. Cleavage and inactivation of protein S by factor Xa may be an additional way in which factor Xa exerts its procoagulant effect, after the initial stages of clot formation.
authors.affiliation: Department of Biochemistry, University of Vermont College of Medicine, Burlington, Vermont 05405-0068, USA. glong@zoo.uvm.edu
authors.forename: G L
authors.initials: GL
authors.lastname: Long
authors.forename: D
authors.initials: D
authors.lastname: Lu
authors.forename: R L
authors.initials: RL
authors.lastname: Xie
authors.forename: M
authors.initials: M
authors.lastname: Kalafatis
mesh_terms: D000595:Amino Acid Sequence; D001777:Blood Coagulation; D002474:Cell-Free System; D004220:Disulfides; D005169:Factor VIII / Q000378:metabolism; D015951:Factor Xa / Q000378:metabolism*; D006487:Hemostasis; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D010743:Phospholipids / Q000378:metabolism; D011485:Protein Binding; D011486:Protein C / Q000378:metabolism; D017293:Protein S / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011994:Recombinant Proteins; D013917:Thrombin / Q000378:metabolism
chemical_list: D004220:Disulfides; D010743:Phospholipids; D011486:Protein C; D017293:Protein S; D011994:Recombinant Proteins; D005169:Factor VIII; D013917:Thrombin; D015951:Factor Xa