Inhibition of cofactor activity of protein S by a complex of protein S and C4b-binding protein. Evidence for inactive ternary complex formation between protein S, C4b-binding protein, and activated protein C.
To elucidate the mechanism by which C4b-binding protein inhibits the cofactor activity of protein S for anticoagulant-activated protein C, the interactions between protein S, activated protein C, and C4b-binding protein were studied using solid-phase enzyme immunoassays. Both activated protein C and C4b-binding protein bound to protein S fixed to microplate wells. C4b-binding protein did not inhibit the binding of activated protein C to protein S, nor did activated protein C inhibit the binding of C4b-binding protein to protein S. Activated protein C bound to a protein S-C4b-binding protein complex which was cross-linked with a chemical reagent as well as it bound to free protein S. Protein S-C4b-binding protein complex competitively inhibited activated protein C-binding to free protein S and also the cofactor activity of free protein S. Immunoblotting analysis showed ternary complex formation with protein S, C4b-binding protein, and activated protein C in the liquid phase by treatment with the cross-linking reagent. These findings suggest that the protein S-C4b-binding protein complex inhibits the cofactor activity of free protein S probably by inhibition of functionally active protein S-activated protein C complex formation by the apparent competitive formation of an inactive ternary complex with protein S, C4b-binding protein, and activated protein C.
Nishioka
J
J
Department of Laboratory Medicine, Mie University School of Medicine, Japan.
Suzuki
K
K
D000911:Antibodies, Monoclonal; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000378:metabolism* / Q000494:pharmacology; D003169:Complement Inactivator Proteins; D003432:Cross-Linking Reagents; D004591:Electrophoresis, Polyacrylamide Gel; D006023:Glycoproteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006801:Humans; D007118:Immunoassay; D015151:Immunoblotting; D010314:Partial Thromboplastin Time; D011486:Protein C / Q000378:metabolism* / Q000494:pharmacology; D017293:Protein S; D013388:Succinimides
D000911:Antibodies, Monoclonal; D002352:Carrier Proteins; D003169:Complement Inactivator Proteins; D003432:Cross-Linking Reagents; D006023:Glycoproteins; D011486:Protein C; D017293:Protein S; D013388:Succinimides; C035760:bis(sulfosuccinimidyl)suberate