Sakurai Y, Fujimura Y, Kokubo T, Imamura K, Kawasaki T, Handa M, Suzuki M, Matsui T, Titani K, Yoshioka A
Department of Pediatrics and Blood Transfusion Medicine, Nara Medical University, Kashihara, Japan.
Thromb Haemost. 1998 Jun;79(6):1199-207.
The entire cDNA sequences of a novel snake venom platelet glycoprotein (GP) Ib-binding protein (BP) composed of an alpha/beta heterodimeric structure, termed mamushigin, from Agkistrodon halys blomhoffii were determined, that include the leader peptides (21/23 amino acid residues) and mature subunits (136/123 amino acid residues). The mature subunits of mamushigin are 37.5% identical, and showed a high degree of similarity (37.7-67.5% identity) with the respective subunits of group VII C-type lectins (19). The sequences of the leader peptides of the mamusigin subunits showed the highest similarity (alpha-73.9/beta-82.6%) with those of factor IX/X-BP from Trimeresurus flavoviridis, and the cleavage site residue in both proteins was the same Ala(-1). The GPIb-binding specificity of mamushigin is strongly supported by several lines of evidence, but mamushigin can directly aggregate normal platelets, similar to alboaggregin-B (AL-B) (1). This differs from other GPIb-BP's. In mamushigin-treated platelets, serotonin was not released, and flow cytometric analysis using a monoclonal antibody PAC-1 totally excluded platelet GPIIb/IIIa activation. Mamushigin enhanced platelet aggregation at low-shear stress, and this effect totally disappeared in the presence of GPIb-receptor blockers specific for von Willebrand factor binding, but not by GPIIb/IIIa-receptor blockers. At high-shear stress, mamushigin blocked platelet aggregation in a dose-dependent manner, as seen with other GPIb-BP's. This paper, therefore, describes the cDNA cloning and molecular characterization of mamushigin which has a different effect on platelet aggregation under different shear stress.
从日本蝮蛇中鉴定出一种新型蛇毒血小板糖蛋白（GP）Ib结合蛋白（BP）的完整cDNA序列，该蛋白由α/β异二聚体结构组成，称为mamushigin，其包括前导肽（分别为21/23个氨基酸残基）和成熟亚基（分别为136/123个氨基酸残基）。Mamushigin的成熟亚基具有37.5%的同源性，并且与VII组C型凝集素的相应亚基显示出高度相似性（同源性为37.7 - 67.5%）。Mamushigin亚基的前导肽序列与竹叶青蛇的因子IX/X - BP的前导肽序列具有最高的相似性（α - 73.9%/β - 82.6%），并且两种蛋白中的切割位点残基均为相同的丙氨酸（-1）。Mamushigin与GPIb的结合特异性得到了多条证据的有力支持，但Mamushigin可以直接使正常血小板聚集，类似于白蝮蛇毒凝集素 - B（AL - B）。这与其他GPIb - BP不同。在经Mamushigin处理的血小板中，5 - 羟色胺未释放，并且使用单克隆抗体PAC - 1进行的流式细胞术分析完全排除了血小板GPIIb/IIIa的激活。Mamushigin在低剪切应力下增强血小板聚集，并且在存在对血管性血友病因子结合具有特异性的GPIb受体阻滞剂时，这种作用完全消失，但在存在GPIIb/IIIa受体阻滞剂时则不会消失。在高剪切应力下，Mamushigin以剂量依赖性方式阻断血小板聚集，这与其他GPIb - BP的情况相同。因此，本文描述了Mamushigin的cDNA克隆和分子特征，其在不同剪切应力下对血小板聚集具有不同的作用。
