van Wijnen M, Stam J G, van't Veer C, Meijers J C, Reitsma P H, Bertina R M, Bouma B N
Department of Haematology, University Hospital Utrecht, The Netherlands.
Thromb Haemost. 1996 Sep;76(3):397-403.
Protein S is a vitamin-K dependent glycoprotein involved in the regulation of the anticoagulant activity of activated protein C (APC). Recent data showed a direct anticoagulant role of protein S independent of APC, as demonstrated by the inhibition of prothrombinase and tenase activity both in plasma and in purified systems. This anticoagulant effect of protein S can be explained either by a direct interaction of protein S with one of the components of the complexes and/or by the interference with the binding of these components to phospholipid surfaces. During our investigation we noted that protein S preparations purified in different ways and derived from different sources, expressed discrepant APC cofactor and direct anticoagulant activity. In order to elucidate these differences and to study the mechanism of the APC-independent activity of protein S, we compared the protein S preparations in phospholipid-binding properties and anticoagulant activity. The dissociation constant for the binding of protein S to immobilized phospholipids ranged from 7 to 74 nM for the different protein S preparations. APC-independent inhibition of both prothrombinase and tenase activity performed on phospholipid vesicles and in plasma showed a strong correlation with the affinity for phospholipids. The APC-independent activity could be abolished by monoclonal antibodies that were either calcium-dependent and/or directed against epitopes in the Gla-region of protein S, suggesting that the protein S-phospholipid interaction is crucial for the APC-independent anticoagulant function of protein S. Protein S preparations with a low APC-independent activity expressed a high APC-cofactor activity suggesting that the affinity of protein S for phospholipids is of less importance in the expression of APC-cofactor activity of protein S. We conclude that high affinity interactions of protein S with the membrane surface are essential for the direct anticoagulant activity of protein S and we suggest that inhibition of the prothrombinase and the tenase complex by protein S is a consequence of the occupation of the phospholipid surface by protein S molecules.
蛋白S是一种维生素K依赖的糖蛋白，参与活化蛋白C（APC）抗凝活性的调节。近期数据显示，蛋白S具有不依赖于APC的直接抗凝作用，这在血浆和纯化系统中对凝血酶原酶和凝血活酶活性的抑制作用中得到了证实。蛋白S的这种抗凝作用可以通过蛋白S与复合物中的一种成分直接相互作用和/或通过干扰这些成分与磷脂表面的结合来解释。在我们的研究过程中，我们注意到以不同方式纯化且来源于不同来源的蛋白S制剂表现出不同的APC辅因子和直接抗凝活性。为了阐明这些差异并研究蛋白S不依赖于APC的活性机制，我们比较了蛋白S制剂在磷脂结合特性和抗凝活性方面的差异。不同蛋白S制剂中蛋白S与固定化磷脂结合的解离常数范围为7至74 nM。在磷脂囊泡和血浆中对凝血酶原酶和凝血活酶活性进行的不依赖于APC的抑制作用与对磷脂的亲和力密切相关。不依赖于APC的活性可被钙依赖性和/或针对蛋白S Gla区域表位的单克隆抗体所消除，这表明蛋白S与磷脂的相互作用对于蛋白S不依赖于APC的抗凝功能至关重要。不依赖于APC活性较低的蛋白S制剂表现出较高的APC辅因子活性，这表明蛋白S对磷脂的亲和力在蛋白S的APC辅因子活性表达中不太重要。我们得出结论，蛋白S与膜表面的高亲和力相互作用对于蛋白S的直接抗凝活性至关重要，并且我们认为蛋白S对凝血酶原酶和凝血活酶复合物的抑制作用是蛋白S分子占据磷脂表面的结果。
