Binding activity of annexin B1 to externalized phosphatidylserine

Objective:To study the binding activity of anne xi n B1 to externalized phosphatidylserine.Methods:Annexin B1 was expressed in E.coli and purified with ion exchange chromatography, then ann e xin B1 labelled with FITC was used to detect the apoptosis of U937 human leukemi c cells and the activation of platelets, which were analyzed by Becton Dickinson FACS Calibur. Results: Labelled annexin B1 not only bound to apoptotic cells but also specifically activated platelets. Considering the affinity, annexin B1 was similar to annexin Ⅴ. Conclusion: Annexin B1 interacts str ongly and specifically with phosphatidylserine (PS) on the outer plasma membrane leaflet of apoptotic cells and activates platelets. Additionally, annexin B1 acts as a potent anticoagulant by binding to platelet membranous phospholipids with higher affinity.