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J. Biol. Chem., Vol. 277, Issue 38, 35124-35132, September 20, 2002

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Ophioluxin, a Convulxin-like C-type Lectin from Ophiophagus hannah (King Cobra) Is a Powerful Platelet Activator via Glycoprotein VI^*

Xiao-Yan Du, Jeannine M. Clemetson, Alexei Navdaev, Edith M. Magnenat^§, Timothy N. C. Wells^§, and Kenneth J. Clemetson^¶

From the  Theodor Kocher Institute, University of Berne, CH-3012 Berne, Switzerland and ^§ Serono Pharmaceutical Research Institute, SA, CH-1228 Geneva, Switzerland

Ophioluxin, a potent platelet agonist, was purified from the venom of Ophiophagus hannah (King cobra). Under nonreducing conditions it has a mass of 85 kDa, similar to convulxin, and on reduction gives two subunits with masses of 16 and 17 kDa, slightly larger than those of convulxin. The N-terminal sequences of both subunits are very similar to those of convulxin and other C-type lectins. Ophioluxin induces a pattern of tyrosine-phosphorylated proteins in platelets like that caused by convulxin, when using appropriate concentrations based on aggregation response, because it is about 2-4 times more powerful as agonist than the latter. Ophioluxin and convulxin induce [Ca²⁺]_i elevation both in platelets and in Dami megakaryocytic cells, and each of these C-type lectins desensitizes responses to the other. Convulxin agglutinates fixed platelets at 2 µg/ml, whereas ophioluxin does not, even at 80 µg/ml. Ophioluxin resembles convulxin more than echicetin or alboaggregin B because polyclonal anti-ophioluxin antibodies recognize both ophioluxin and convulxin, but not echicetin, and platelets adhere to and spread on ophioluxin- or convulxin-precoated surfaces in the same way that is clearly different from their behavior on an alboaggregin B surface. Immobilized ophioluxin was used to isolate the glycoprotein VI-Fc complex from resting platelets, which also contained Fyn, Lyn, Syk, LAT, and SLP76. Ophioluxin is the first multiheterodimeric, convulxin-like snake C-type lectin, as well as the first platelet agonist, to be described from the Elapidae snake family.

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