title: A novel viper venom metalloproteinase, alborhagin, is an agonist at the platelet collagen receptor GPVI.
abstract: The interaction of platelet membrane glycoprotein VI (GPVI) with collagen can initiate (patho)physiological thrombus formation. The viper venom C-type lectin family proteins convulxin and alboaggregin-A activate platelets by interacting with GPVI. In this study, we isolated from white-lipped tree viper (Trimeresurus albolabris) venom, alborhagin, which is functionally related to convulxin because it activates platelets but is structurally different and related to venom metalloproteinases. Alborhagin-induced platelet aggregation (EC50, <7.5 microg/ml) was inhibitable by an anti-alphaIIbbeta3 antibody, CRC64, and the Src family kinase inhibitor PP1, suggesting that alborhagin activates platelets, leading to alphaIIbbeta3-dependent aggregation. Additional evidence suggested that, like convulxin, alborhagin activated platelets by a mechanism involving GPVI. First, alborhagin- and convulxin-treated platelets showed a similar tyrosine phosphorylation pattern, including a similar level of phospholipase Cgamma2 phosphorylation. Second, alborhagin induced GPVI-dependent responses in GPVI-transfected K562 and Jurkat cells. Third, alborhagin-dependent aggregation of mouse platelets was inhibited by the anti-GPVI monoclonal antibody JAQ1. Alborhagin had minimal effect on convulxin binding to GPVI-expressing cells, indicating that these venom proteins may recognize distinct binding sites. Characterization of alborhagin as a GPVI agonist that is structurally distinct from convulxin demonstrates the versatility of snake venom toxins and provides a novel probe for GPVI-dependent platelet activation.
authors.affiliation: Hazel and Pip Appel Vascular Biology Laboratory and the Peptide Biology Laboratory, Baker Medical Research Institute, Melbourne 8008, Australia. rkandrews@hotmail.com
authors.forename: R K
authors.initials: RK
authors.lastname: Andrews
authors.forename: E E
authors.initials: EE
authors.lastname: Gardiner
authors.forename: N
authors.initials: N
authors.lastname: Asazuma
authors.forename: O
authors.initials: O
authors.lastname: Berlanga
authors.forename: D
authors.initials: D
authors.lastname: Tulasne
authors.forename: B
authors.initials: B
authors.lastname: Nieswandt
authors.forename: A I
authors.initials: AI
authors.lastname: Smith
authors.forename: M C
authors.initials: MC
authors.lastname: Berndt
authors.forename: S P
authors.initials: SP
authors.lastname: Watson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000378:metabolism; D001665:Binding Sites; D001667:Binding, Competitive; D001792:Blood Platelets / Q000378:metabolism; D002460:Cell Line; D003435:Crotalid Venoms / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000378:metabolism; D005340:Fibrinogen / Q000378:metabolism; D006801:Humans; D019169:Jurkat Cells; D020014:K562 Cells; D037102:Lectins / Q000737:chemistry; D037181:Lectins, C-Type; D008666:Metalloendopeptidases / Q000737:chemistry* / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010940:Plant Proteins / Q000378:metabolism; D015539:Platelet Activation; D010980:Platelet Membrane Glycoproteins / Q000819:agonists*; D011233:Precipitin Tests; D011485:Protein Binding; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012910:Snake Venoms; D013696:Temperature; D014162:Transfection; D014757:Viper Venoms / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D000906:Antibodies; D003435:Crotalid Venoms; D004268:DNA-Binding Proteins; D037102:Lectins; D037181:Lectins, C-Type; C083693:PP1 protein, Physcomitrella patens; D010940:Plant Proteins; D010980:Platelet Membrane Glycoproteins; D012910:Snake Venoms; D014757:Viper Venoms; C098341:platelet membrane glycoprotein VI; C028890:convulxin; D005340:Fibrinogen; D008666:Metalloendopeptidases; C433245:alborhagin