Maheshwari Neeraj, Kantipudi Satish, Maheshwari Anand, Arora Kashika, Kwatra Neha, Sahni Girish
CSIR-Institute of Microbial Technology, Chandigarh, India.
PLoS One. 2016 Mar 14;11(3):e0150315. doi: 10.1371/journal.pone.0150315. eCollection 2016.
Streptokinase (SK) is a potent clot dissolver but lacks fibrin clot specificity as it activates human plasminogen (HPG) into human plasmin (HPN) throughout the system leading to increased risk of bleeding. Another major drawback associated with all thrombolytics, including tissue plasminogen activator, is the generation of transient thrombin and release of clot-bound thrombin that promotes reformation of clots. In order to obtain anti-thrombotic as well as clot-specificity properties in SK, cDNAs encoding the EGF 4,5,6 domains of human thrombomodulin were fused with that of streptokinase, either at its N- or C-termini, and expressed these in Pichia pastoris followed by purification and structural-functional characterization, including plasminogen activation, thrombin inhibition, and Protein C activation characteristics. Interestingly, the N-terminal EGF fusion construct (EGF-SK) showed plasmin-mediated plasminogen activation, whereas the C-terminal (SK-EGF) fusion construct exhibited 'spontaneous' plasminogen activation which is quite similar to SK i.e. direct activation of systemic HPG in absence of free HPN. Since HPN is normally absent in free circulation due to rapid serpin-based inactivation (such as alpha-2-antiplasmin and alpha-2-Macroglobin), but selectively present in clots, a plasmin-dependent mode of HPG activation is expected to lead to a desirable fibrin clot-specific response by the thrombolytic. Both the N- and C-terminal fusion constructs showed strong thrombin inhibition and Protein C activation properties as well, and significantly prevented re-occlusion in a specially designed assay. The EGF-SK construct exhibited fibrin clot dissolution properties with much-lowered levels of fibrinogenolysis, suggesting unmistakable promise in clot dissolver therapy with reduced hemorrhage and re-occlusion risks.
链激酶(SK)是一种有效的血栓溶解剂,但缺乏纤维蛋白凝块特异性,因为它会在整个系统中将人纤溶酶原(HPG)激活为人纤溶酶(HPN),从而增加出血风险。与所有溶栓剂(包括组织纤溶酶原激活剂)相关的另一个主要缺点是会产生短暂的凝血酶并释放与凝块结合的凝血酶,从而促进血栓的重新形成。为了使SK具有抗血栓形成以及凝块特异性的特性,编码人血栓调节蛋白EGF 4、5、6结构域的cDNA在其N端或C端与链激酶的cDNA融合,并在毕赤酵母中表达,随后进行纯化以及结构功能表征,包括纤溶酶原激活、凝血酶抑制和蛋白C激活特性。有趣的是,N端EGF融合构建体(EGF-SK)表现出纤溶酶介导的纤溶酶原激活,而C端(SK-EGF)融合构建体表现出“自发”的纤溶酶原激活,这与SK非常相似,即在没有游离HPN的情况下直接激活全身HPG。由于HPN在自由循环中通常由于基于丝氨酸蛋白酶抑制剂的快速失活(如α-2-抗纤溶酶和α-2-巨球蛋白)而不存在,但选择性地存在于凝块中,因此纤溶酶依赖性的HPG激活模式有望导致溶栓剂产生理想的纤维蛋白凝块特异性反应。N端和C端融合构建体均表现出较强的凝血酶抑制和蛋白C激活特性,并且在一项专门设计的试验中显著防止了再闭塞。EGF-SK构建体表现出纤维蛋白凝块溶解特性,同时纤维蛋白原溶解水平大大降低,这表明在降低出血和再闭塞风险的溶栓治疗中具有明确的前景。