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Wen-Jeng Wang, Qing-Dong Ling, Ming-Yi Liau, Tur-Fu Huang
A tetrameric glycoprotein Ib-binding protein, agglucetin, from Formosan pit viper: structure and interaction with human platelets
Agglucetin, a tetrameric agglutination inducer from the Formosan pit viper, has been identified as a platelet membrane glycoprotein (GP) Ib agonist and directly agglutinated fixed-platelets in the absence of von Willebrand factor (vWf). Here, we resolved the complete cDNA sequences of agglucetin subunits (1, 2, 1 and 2) by molecular cloning. Each cloned cDNA encoding the leader peptide (23 residues) and the mature subunit (131/135/123/126 residues) shares a high degree of homology to each other and the C-type lectin-like GP Ib-binding proteins (BPs). Furthermore, agglucetin specifically caused platelet agglutination and surface exposure of integrin IIb3 with a GPIb-dependent manner in washed platelets, based on the observation that the enhanced expression of functional IIb3 was suppressed by a GPIb-cleaving metalloproteinase, crotalin. Pretreating platelets with staurosporine or BAPTA-AM also completely blocked the exposure of functional IIb3, suggesting that the activation of protein kinase C and intracellular calcium mobilization are involved in the GPIb-dependent signaling. In human platelet-rich plasma (PRP), agglucetin elicited sequential biphasic responses of platelet agglutination and aggregation in a GPIb- and IIb3-dependent manner, respectively, implying that other cofactors may amplify platelet activation to trigger aggregation.
Thrombosis and Haemostasis, Schattauer
Print ISSN: 0340-6245
Volume: 90, 09/2003
Pages: 465 - 475