Lysenin, a Sphingomyelin-Binding Protein: its Role in the Activation of Platelets

Lysenin is a novel protein of 33 kDa isolated from the earthworm, Eisenia foetida, and it binds specifically to sphingomyelin (SM) among the phospholipids located in the cell membrane. Since it is known that SM is rich inthe cell membrane of platelets, we evaluated the effects of lysenin on platelets. Flow cytometric analysis revealed that lysenin bound to platelets in a concentration dependent manner (1-100 ng/mL). Moreover, lysenin (1μg/mL) induced irreversible aggregations of platelets with formation of thromboxane B 2 . The expressions of P-selectin and platelet endothelial cell adhesion molecule-1 (PECAM-1) on the surface of platelets were increased 5 min after the incubation of platelets with lysenin (10-100 ng/mL). These results indicate that SM in the cell membrane is involved in activation of platelets by lysenin. Lysenin might be a useful tool for studying the mechanisms of the platelet activation.