Wojta J, Beckmann R, Turcu L, Wagner O F, van Zonneveld A J, Binder B R
Department of Medical Physiology, University of Vienna, Austria.
J Biol Chem. 1989 May 15;264(14):7957-61.
Fibrin interacts with tissue-type plasminogen activator (tPA) via the finger and the kringle 2 domains. Three monoclonal antibodies against tPA, designated MPW3VPA, MPW6VPA, and MPW7VPA, which react with epitopes in the tPA molecule involved in fibrin binding, were characterized. The IgM monoclonal antibody MPW6VPA, directed against an epitope close to the finger and epidermal growth factor domains, stimulated plasminogen activation only in the absence of CNBr-fibrinogen fragments by increasing kcat in a dose-dependent fashion, an effect which was not restricted to the intact molecule. These results suggest that MPW6VPA mimics the initial effect of fibrin bound to the tPA molecule, which results in a change of kcat values. The MPW6VPA effect was reversed by another antibody, MPW3VPA, also directed against epidermal growth factor and finger domains. The latter antibody also inhibited plasminogen activation by tPA in the presence of CNBr-fibrinogen fragments in a dose-dependent, apparently noncompetitive way. No effect of MPW3VPA was seen in the absence of CNBr-fibrinogen fragments. MPW7VPA directed against kringle 2 of tPA inhibited plasminogen activation by tPA only when CNBr-fibrinogen fragments were present. This inhibition was apparently competitive and dose-dependent. These data suggest that MPW3VPA interferes with the first phase of fibrin binding to tPA, whereas MPW7VPA interferes with the second phase of fibrin binding to the tPA molecule via kringle 2, resulting in Km changes.
纤维蛋白通过指状结构域和kringle 2结构域与组织型纤溶酶原激活剂（tPA）相互作用。对三种针对tPA的单克隆抗体（分别命名为MPW3VPA、MPW6VPA和MPW7VPA）进行了特性鉴定，它们与tPA分子中参与纤维蛋白结合的表位发生反应。IgM单克隆抗体MPW6VPA针对靠近指状结构域和表皮生长因子结构域的一个表位，仅在不存在CNBr - 纤维蛋白原片段的情况下，通过剂量依赖性增加kcat来刺激纤溶酶原激活，这种效应并不局限于完整分子。这些结果表明，MPW6VPA模拟了与tPA分子结合的纤维蛋白的初始效应，这导致了kcat值的变化。MPW6VPA的效应被另一种同样针对表皮生长因子和指状结构域的抗体MPW3VPA逆转。后一种抗体在存在CNBr - 纤维蛋白原片段的情况下，也以剂量依赖性、明显非竞争性的方式抑制tPA介导的纤溶酶原激活。在不存在CNBr - 纤维蛋白原片段的情况下未观察到MPW3VPA的作用。针对tPA的kringle 2的MPW7VPA仅在存在CNBr - 纤维蛋白原片段时抑制tPA介导的纤溶酶原激活。这种抑制显然是竞争性的且呈剂量依赖性。这些数据表明，MPW3VPA干扰纤维蛋白与tPA结合的第一阶段，而MPW7VPA通过kringle 2干扰纤维蛋白与tPA分子结合的第二阶段，导致Km值改变。
