Domain Structure of Protein S: GLA Region: contains g-carboxyglutamic acid residues, EGF Region: contains sequences homologous to human epidermal growth factor, TSR = Thrombin sensitive region, Region of unknown function which replaces the catalytic triad found in vitamin K-dependent serine proteases. Protein S is a single chain vitamin K-dependent protein which is thought to function in both the coagulation and complement cascades (1,2). Approximately 60% of protein S circulating in plasma is complexed to C4b binding protein (C4BP). It has been suggested that g-carboxyglutamic acid (gla) dependent binding of protein S to negatively charged phospholipids may function to concentrate C4BP at cell surfaces following injury. In the coagulation system, Protein S functions as an anticoagulant cofactor protein. Activated Protein C (APC) forms a 1:1 stoichiometric complex with Protein S in the presence of Ca2+ and phospholipid vesicles (Kd=6x10e-9M) (3). In the presence of Protein S, a moderate increase (3-10 fold) in the rate of factor Va and factor VIIIa inactivation by APC is observed in plasma and on the surface of unstimulated platelets. Protein S bound to C4BP does not possess APC cofactor activity. Recently, an additional binding protein which enhances the activity of Protein S has been described (4). Proteolytic inactivation of Protein S by thrombin has been proposed as a regulatory mechanism in this system. A single cleavage by thrombin abolishes Protein S cofactor activity by removing an NH2-terminal peptide (Mr=8000) which contains the gla domain. The domain structure of Protein S is similar to that of the other vitamin K-dependent coagulation factors with the exception that Protein S does not possess the catalytic triad. Protein S is a single chain protein containing 10 gla residues in the NH2-terminal domain and 4 epidermal growth factor (EGF) domains. Localization: Plasma, free and complexed to C4BP Plasma Concentration: 10ug/ml (free) (6) Mode of Action: Cofactor for Activated Protein C Extinction Coefficient: E1%1cm, 280nm=9.5 (7) Isoelectric Point: 5.0-5.5 (7) Structure: Single chain, NH2-terminal gla domain, four EGF domains Percent Carbohydrate: 7% (7) Post-translational Modifications: One b-hydroxyaspartate (8) ten gla residues (7), three b-hydroxyasparagine (8). Amyloid A, Serum, Human
Molecular Weight:
69
Purity:
95% by SDS-PAGE. Human Protein S is isolated from fresh frozen plasma by a combination of conventional methods and immunoaffinity chromatography as described by Jenny, et al. Purity is determined by SDS-PAGE analysis.
Form:
Supplied as a liquid in 50% glycerol, H2O.
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