Annexin V (ANXA5)

(or annexin V) is a cellular protein in the annexin group. The function of the protein is unknown, however annexin A5 has been proposed to play a role in the inhibition of blood coagulation by competing for phosphatidylserine binding sites with prothrombin and also to inhibit the activity of phospholipase A1. These properties have been found by in vitro experiments. Antibodies directed against annexin A5 are the cause of a syndrome called the antiphospholipid syndrome. Annexin A5 is used as a probe in the annexin A5 affinity assay to detect cells that have expressed phosphatidylserine on the cell surface, a feature found in apoptosis as well as other forms of cell death. Platelets also expose phosphatidylserine on their surface when activated, which serves as binding site for various coagulation factors.