Plasminogen Activation & SK: Structure-Function

描述（由申请人提供）：纤溶酶原（Pg）系统溶解引起心脏病发作和中风的血栓（血凝块）。Pg系统通过与抑制剂、激活剂、底物等的蛋白质-蛋白质相互作用来严格调节。链激酶（SK）和其他Pg激活剂将Pg裂解为纤溶酶，启动纤维蛋白溶解（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，机械的见解Pg系统的调节，可以进一步降低心脏病发作的死亡率，并改善中风，肺栓塞等的治疗，因为它的生理和治疗的重要性，我们的长期目标是帮助阐明蛋白质-蛋白质相互作用，调节和修改的Pg系统的活动。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接触。在第一阶段进行的研究，这项赠款已帮助描绘优雅的互动，通过SK转换PG已经对定义以下机制进行了深入研究：1）SK与Pg形成紧密稳定的“激活剂复合物”2）SK非蛋白水解地在Pg中产生潜在活性位点，产生“原始酶”（Pg*），和3）SK修饰Pg* 或纤溶酶的底物特异性，使得复合物可以切割Pg分子。这个延续的建议是针对进一步解剖的过程中的间接Pg激活，以确定新的机制，其中SK成为纤维蛋白依赖性（或t-PA样酶），以确定纤维蛋白依赖性SK是否具有成为上级纤维蛋白溶解剂的潜力，以了解Pg kringle结构域在间接Pg激活中的作用，定义SK型机制所需的SK-Pg复合物中发生的分子间相互作用。从广泛的科学意义上说，对这一独特的间接Pg激活过程的了解将扩大我们对Pg系统的催化活性和特异性如何调节的理解，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.