L-amino acid oxidase from Naja atra venom activates and binds to human platelets

Li, Rui; Zhu, Shaowen; Wu, Jianbo; Wang, Wanyu; Lu, Qiumin; Clemetson, Kenneth J (2008). L-amino acid oxidase from Naja atra venom activates and binds to human platelets. Acta biochimica et biophysica Sinica - ABBS, 40(1), pp. 19-26. Shanghai: Inst. of Biochemistry and Cell Biology 10.1111/j.1745-7270.2008.00372.x

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An L-amino acid oxidase (LAAO), NA-LAAO, was purified from the venom of Naja atra. Its N-terminal sequence shows great similarity with LAAOs from other snake venoms. NA-LAAO dose-dependently induced aggregation of washed human platelets. However, it had no activity on platelets in platelet-rich plasma. A low concentration of NA-LAAO greatly promoted the effect of hydrogen peroxide, whereas hydrogen peroxide itself had little activation effect on platelets. NA-LAAO induced tyrosine phosphorylation of a number of platelet proteins including Src kinase, spleen tyrosine kinase, and phospholipase Cgamma2. Unlike convulxin, Fc receptor gamma chain and T lymphocyte adapter protein are not phosphorylated in NA-LAAO-activated platelets, suggesting an activation mechanism different from the glycoprotein VI pathway. Catalase inhibited the platelet aggregation and platelet protein phosphorylation induced by NA-LAAO. NA-LAAO bound to fixed platelets as well as to platelet lysates of Western blots. Furthermore, affinity chromatography of platelet proteins on an NA-LAAO-Sepharose 4B column isolated a few platelet membrane proteins, suggesting that binding of NA-LAAO to the platelet membrane might play a role in its action on platelets.

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