Pechik Igor, Yakovlev Sergiy, Mosesson Michael W, Gilliland Gary L, Medved Leonid
Center for Advanced Research in Biotechnology, University of Maryland Biotechnology Institute and National Institute of Standards and Technology, Rockville, Maryland 20850, USA.
Biochemistry. 2006 Mar 21;45(11):3588-97. doi: 10.1021/bi0525369.
Nonsubstrate interaction of thrombin with fibrinogen promotes sequential cleavage of fibrinopeptides A and B (fpA and fpB, respectively) from the latter, resulting in its conversion into fibrin. The recently established crystal structure of human thrombin in complex with the central part of human fibrin clarified the mechanism of this interaction. Here, we reveal new details of the structure and present the results of molecular modeling of the fpA- and fpB-containing portions of the Aalpha and Bbeta chains, not identified in the complex, in both fibrinogen and protofibrils. The analysis of the results reveals that in fibrinogen the fpA-containing portions are in a more favorable position to bind in the active site cleft of bound thrombin. Surface plasmon resonance experiments establish that the fpB-containing portions interact with the fibrin-derived dimeric D-D fragment, suggesting that in protofibrils they bind to the newly formed DD regions bringing fpB into the vicinity of bound thrombin. These findings provide a coherent rationale for the preferential removal of fpA from fibrinogen at the first stage of fibrin assembly and the accelerated cleavage of fpB from protofibrils and/or fibrils at the second stage.
凝血酶与纤维蛋白原的非底物相互作用促进了纤维蛋白肽A和B（分别为fpA和fpB）从后者的顺序裂解，导致其转化为纤维蛋白。最近建立的人凝血酶与人类纤维蛋白中心部分复合物的晶体结构阐明了这种相互作用的机制。在这里，我们揭示了结构的新细节，并展示了在纤维蛋白原和原纤维中未在复合物中鉴定的Aα和Bβ链含fpA和fpB部分的分子建模结果。结果分析表明，在纤维蛋白原中，含fpA的部分在结合的凝血酶活性位点裂隙中结合的位置更有利。表面等离子体共振实验表明，含fpB的部分与纤维蛋白衍生的二聚体D-D片段相互作用，这表明在原纤维中它们与新形成的DD区域结合，使fpB靠近结合的凝血酶。这些发现为纤维蛋白组装第一阶段从纤维蛋白原中优先去除fpA以及第二阶段从原纤维和/或纤维中加速裂解fpB提供了连贯的理论依据。
