A novel viper venom metalloproteinase, alborhagin, is an agonist at the platelet collagen receptor GPVI.
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.
Andrews
R K
RK
Hazel and Pip Appel Vascular Biology Laboratory and the Peptide Biology Laboratory, Baker Medical Research Institute, Melbourne 8008, Australia. rkandrews@hotmail.com
Gardiner
E E
EE
Asazuma
N
N
Berlanga
O
O
Tulasne
D
D
Nieswandt
B
B
Smith
A I
AI
Berndt
M C
MC
Watson
S P
SP
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*
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