Direct anticoagulant activity of protein S-C4b binding protein complex in Heerlen heterozygotes and normals.

Abstract

BACKGROUND:

Plasma protein S normally circulates free (40%) or complexed with C4b-binding protein (PS-C4BP); only free protein S is a cofactor for activated protein C during factor (F) Va inactivation. Protein S-Heerlen lacks a carbohydrate group, leading to low plasma free protein S levels, but normal levels of PS-C4BP.

OBJECTIVES:

Because protein S-Heerlen is not associated with thrombosis, we investigated whether PS-C4BP is directly anticoagulant in plasma and whether PS-Heerlen-C4BP has enhanced direct anticoagulant activity.

METHODS:

An assay for protein S direct activity was applied to Heerlen-heterozygous plasmas. Free and complexed protein S were repeatedly isolated from normal and Heerlen-heterozygous plasmas and tested for direct anticoagulant activity in prothrombinase assays and in plasma.

RESULTS:

Heerlen-heterozygous plasmas were deficient in free and total protein S antigen but had normal to high protein S direct anticoagulant activity. Purified Heerlen-heterozygous PS-C4BP was 7-fold more potent than normal PS-C4BP in inhibiting full prothrombinase activity, and 22-fold more potent in inhibiting prothrombin activation in the absence of FVa; it also specifically prolonged plasma clotting times 14-fold more than normal PS-C4BP. Heerlen-heterozygous PS-C4BP did not compete for limiting phospholipids any better than normal PS-C4BP. However, ligand blots and surface plasmon resonance studies showed that Heerlen-heterozygous PS-C4BP bound more avidly to FXa than did normal PS-C4BP (apparent Kd = 4.3 nm vs. 82 nm).

CONCLUSIONS:

Plasma-derived PS-C4BP has direct anticoagulant activity in plasma and in purified systems. Enhanced direct activity of PS-Heerlen-C4BP may compensate for low free protein S levels and low cofactor activity in individuals with protein S-Heerlen.

• Authors: M J Heeb, R R Koenen, J A Fernández, T M Hackeng
• Journal: Journal of thrombosis and haemostasis : JTH (J Thromb Haemost) Vol. 2 Issue 10 Pg. 1766-73 (Oct 2004) ISSN: 1538-7933 [Print] England
• PMID: 15456488 (Publication Type: Comparative Study, Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Anticoagulants
• C4BPA protein, human
• Complement C4b-Binding Protein
• Histocompatibility Antigens
• Phospholipids
• Protein S
• protein S Heerlen
• Prothrombin
• Thromboplastin
• Factor Xa

Topics

• Adult
• Anticoagulants
• Blood Coagulation Tests
• Blood Platelets
• Complement C4b-Binding Protein
• Factor Xa (metabolism)
• Family Health
• Female
• Heterozygote
• Histocompatibility Antigens (metabolism, physiology)
• Humans
• Male
• Phospholipids
• Protein Binding (genetics)
• Protein S (analysis, metabolism, physiology)
• Prothrombin (antagonists & inhibitors)
• Thromboplastin (antagonists & inhibitors)