Annexin A5

Annexin A5 (or annexin V) is a is_associated_with::cellular protein in the is_associated_with::annexin group. The function of the is_associated_with::protein is unknown; however, annexin A5 has been proposed to play a role in the inhibition of blood is_associated_with::coagulation by competing for is_associated_with::phosphatidylserine binding sites with is_associated_with::prothrombin and also to inhibit the activity of phospholipase A1. These properties have been found by is_associated_with::in vitro experiments.

Annexin A5 in pathology
is_associated_with::Antibodies directed against annexin A5 are found in patients with a disease called the is_associated_with::antiphospholipid syndrome (APS), a thrombophilic disease associated with autoantibodies against phospholipid compounds.

Annexin A5 forms a shield around negatively charged phospholipid molecules. The formation of an annexin A5 shield blocks the entry of phospholipids into is_associated_with::coagulation (clotting) reactions. In the antiphospholipid antibody syndrome, the formation of the shield is disrupted by antibodies. Without the shield, there is an increased quantity of phospholipid molecules on cell membranes, speeding up coagulation reactions and causing the blood-clotting characteristic of the antiphospholipid antibody syndrome.

Annexin A5 showed upregulation in is_associated_with::papillary thyroid carcinoma.

Laboratory use of annexin A5
Annexin A5 is used as a non-quantitative probe to detect cells that have expressed is_associated_with::phosphatidylserine (PS) on the cell surface, an event found in is_associated_with::apoptosis as well as other forms of cell death. is_associated_with::Platelets also expose PS and PE on their surface when activated, which serves as binding site for various coagulation factors.

The is_associated_with::annexin A5 affinity assay typically uses a conjugate of annexin V and a fluorescent or enzymatic label, biotin or other tags, or a radioelement, in a suitable buffer (annexin V binding to aminophospholipids is Ca2+ dependent). The assay combines annexin V staining of PS and PE membrane events with the staining of proteins in the cell nucleus with is_associated_with::propidium iodide (PI) or is_associated_with::7-Aminoactinomycin D (AAD-7), distinguishing viable cells from is_associated_with::apoptotic cells and is_associated_with::necrotic cells. Detection occurs by is_associated_with::flow cytometry or a is_associated_with::fluorescence microscope.

Interactions
Annexin A5 has been shown to interact with is_associated_with::Kinase insert domain receptor and is_associated_with::Integrin, beta 5.