Stejnulxin, a novel snake C-type lectin-like protein from Trimeresurus stejnegeri venom is a potent platelet agonist acting specifically via GPVI

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Abstract
Stejnulxin, a novel snake C-type lectin-like protein with potent platelet activating activity, was purified and characterized from Trimeresurus stejnegeri venom. Under non-reducing conditions, it migrated on a SDS-polyacrylamide gel with an apparent molecular mass of 120 kDa. On reduction, it separated into three polypeptide subunits with apparent molecular masses of 16 kDa (α), 20 kDa (β1) and 22 kDa (β2), respectively. The complete amino acid sequences of its subunits were deduced from cloned cDNAs. The N-terminal sequencing and cDNA cloning indicated that β1 and β2 subunits of stejnulxin have identical amino acid sequences and each contains two N-glycosylation sites. Accordingly, the molecular mass difference between β1 and β2 is caused by glycosylation heterogenity. The subunit amino acid sequences of stejnulxin are similar to those of convulxin, with sequence identities of 52.6% and 66.4% for the α and β, respectively. Stejnulxin induced human platelet aggregation in a dose-dependent manner. Antibodies against αIIbβ3 inhibited the aggregation response to stejnulxin, indicating that activation of αIIbβ3 and binding of fibrinogen are involved in stejnulxin-induced platelet aggregation. Antibodies against GPIbα or α2β1 as well as echicetin or rhodocetin had no significant effect on stejnulxin-induced platelet aggregation. However, platelet activation induced by stejnulxin was blocked by anti-GPVI antibodies. In addition, stejnulxin induced a tyrosine phosphorylation profile in platelets that resembled that produced by convulxin. Biotinylated stejnulxin bound specifically to platelet membrane GPVI.

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