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

Summary

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 α_IIbβ₃ inhibited the aggregation response to stejnulxin, indicating that activation of α_IIbβ₃ 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.

Keywords

Stejnulxin - platelet aggregation - GPVI - tyrosine phosphorylation

• References

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