Annexin A5

Annexin A5 is a phospholipid binding protein, which binds with high affinity and selectivity to PS in the presence of calcium. PS is predominantly located in membrane leaflets, which face the cytosol. However, recent findings show that each cell type has the molecular machinery to expose PS at its cell surface. This machinery is activated during the execution of apoptosis. Once PS is exposed at the cell surface it exhibits procoagulant and proinflammatory activities. Annexin A5 will bind to the PS-exposing apoptotic cell and can inhibit the procoagulant and proinflammatory activities of the dying cell. Annexin A5 has also been identified as an anticoagulant protein in the blood coagulation cascade, by acting as an inhibitor of prothrombin activation. The presence of antibodies to Annexin A5 is associated with systemic lupus erythematosus (SLE), recurrent spontaneous abortions and systemic sclerosis (SSc).