title: A tetrameric glycoprotein Ib-binding protein, agglucetin, from Formosan pit viper: structure and interaction with human platelets.
abstract: 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 (alpha(1), alpha(2), beta(1) and beta(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 alpha(IIb)beta(3) with a GPIb-dependent manner in washed platelets, based on the observation that the enhanced expression of functional alpha(IIb)beta(3) was suppressed by a GPIb-cleaving metalloproteinase, crotalin. Pretreating platelets with staurosporine or BAPTA-AM also completely blocked the exposure of functional alpha(IIb)beta(3), 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 alpha(IIb)beta(3)-dependent manner, respectively, implying that other cofactors may amplify platelet activation to trigger aggregation.
authors.affiliation: Department of Nursing, Chang-Gung Institute of Technology, Kwei-Shan, Tao-Yuan, Taiwan.
authors.forename: Wen-Jeng
authors.initials: WJ
authors.lastname: Wang
authors.forename: Qing-Dong
authors.initials: QD
authors.lastname: Ling
authors.forename: Ming-Yi
authors.initials: MY
authors.lastname: Liau
authors.forename: Tur-Fu
authors.initials: TF
authors.lastname: Huang
mesh_terms: D000818:Animals; D001483:Base Sequence; D001792:Blood Platelets / Q000187:drug effects*; D003001:Cloning, Molecular; D003435:Crotalid Venoms / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology*; D006801:Humans; D008969:Molecular Sequence Data; D010974:Platelet Aggregation / Q000187:drug effects; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000187:drug effects; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000819:agonists; D010980:Platelet Membrane Glycoproteins; D020836:Protein Structure, Quaternary; D017422:Sequence Analysis, DNA
chemical_list: D003435:Crotalid Venoms; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; C453260:agglucetin; C032193:glycoprotein receptor GPIb-IX