Plasminogen Activation & SK: Structure-Function

描述(申请人提供)：纤溶酶原(PG)系统可溶解导致心脏病发作和中风的血栓(血栓)。PG系统受到与抑制剂、激活剂、底物等蛋白质-蛋白质相互作用的严格调控。PG被链激酶(SK)和其他PG激活剂切割成纤溶酶，启动纤溶(凝块溶解)，从而挽救心脏病发作患者的生命。最近的研究表明，对PG系统调节的机械性见解可以进一步降低心脏病发作的死亡率，并改进中风、肺栓塞等的治疗。由于PG系统的生理学和治疗重要性，我们的长期目标是帮助阐明调节和修改PG系统活性的蛋白质-蛋白质相互作用。PG和间接PG激活剂SK之间的相互作用是这些接触中最重要的生物学和医学联系之一。在这笔赠款的第一阶段进行的研究帮助描绘了SK将PG(没有切割)转化为最具催化效率的PG激活剂的优雅相互作用，洞察力已经被用来定义如下机制：1)SK与PG(或纤溶酶)形成紧密稳定的‘激活剂复合体’，2)SK非蛋白水解性地在PG中产生潜在的活性部位，产生‘处女酶’(PG*)，以及3)SK修饰PG*或纤溶酶的底物专一性，从而使该复合体能够切割PG分子。这一继续方案旨在进一步剖析PG间接激活的过程，以确定SK成为纤维蛋白依赖(或t-PA样酶)的新机制，确定纤维蛋白依赖的SK是否具有成为优秀纤溶剂的潜力，了解PG环区在PG间接激活中的作用，以及定义SK-PG复合体中发生的分子间相互作用，这是SK类型机制所必需的。在广泛的科学意义上，深入了解这一独特的间接PG激活过程将扩大我们对PG系统催化活性和特异性调节的理解，并可能提出合理的方法来改变间接PG激活剂，以提高其对血栓形成患者的治疗价值。

DESCRIPTION (provided by applicant): The plasminogen (Pg) system dissolves the thrombi (blood clots) that cause heart attacks and strokes. The Pg system is tightly regulated by protein-protein interactions with inhibitors, activators, substrates, etc. The cleavage of Pg to plasmin by streptokinase (SK), and other Pg activators, initiates fibrinolysis (clot dissolution) which saves the lives of heart attack patients. Recent studies have suggested that mechanistic insights into the regulation of the Pg system could further reduce the mortality from heart attacks, and improve the treatment of strokes, pulmonary embolism, etc. Because of its physiologic and therapeutic importance, our long term goal is to help elucidate the protein-protein interactions that regulate and modify the activity of the Pg system. The interactions between Pg and the indirect Pg activator SK are among the most biologically and medically important of these contacts. Studies performed in the first phase of this grant have helped to delineate the elegant interactions through which SK converts Pg (without cleavage) into the most catalytically efficient Pg activator, Insights have been made into defining the mechanisms through which: 1) SK forms a tight stable 'activator complex' with Pg (or plasmin), 2) SK non-proteolytically generates the latent active site in Pg creating a 'virgin enzyme' (Pg*), and 3) SK modifies the substrate specificity of Pg* or plasmin so that the complex can cleave Pg molecules. This continuation proposal is directed towards further dissecting the process of indirect Pg activation, in order to determine the novel mechanisms by which SK becomes a fibrin-dependent (or t-PA-like enzyme), to define whether fibrin-dependent SKs have the potential to be superior fibrinolytic agents, to understand the role of the Pg kringle domains in indirect Pg activation and, to define the intermolecular interactions that occur in the SK-Pg complex which are required for a SK-type of mechanism. In a broad scientific sense, insights into this unique process of indirect Pg activation should enlarge our understanding of how the catalytic activity and specificity of Pg system is regulated, and could suggest rational ways to alter the indirect Pg activators so as to improve their therapeutic value for patients with thrombosis.