Annexin A5
Encyclopedia
Annexin A5 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.
(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 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.
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.
with Kinase insert domain receptor
and Integrin, beta 5
.
Annexin
Annexin is a common name for a group of cellular proteins. They are found in all kingdoms with the exception of the bacteria....
group. The function of the protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
is unknown; however, annexin A5 has been proposed to play a role in the inhibition of blood coagulation
Coagulation
Coagulation is a complex process by which blood forms clots. It is an important part of hemostasis, the cessation of blood loss from a damaged vessel, wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel...
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
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...
experiments.
Annexin A5 in pathology
Antibodies directed against annexin A5 are found in patients with a disease called the antiphospholipid syndromeAntiphospholipid syndrome
Antiphospholipid syndrome or antiphospholipid antibody syndrome , often also Hughes syndrome, is an autoimmune, hypercoagulable state caused by antibodies against cell-membrane phospholipids that provokes blood clots in both arteries and veins as well as pregnancy-related complications such as...
(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 coagulation
Coagulation
Coagulation is a complex process by which blood forms clots. It is an important part of hemostasis, the cessation of blood loss from a damaged vessel, wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel...
(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.
Laboratory use of annexin A5
Annexin A5 is used as a probe in the annexin A5 affinity assayAnnexin A5 affinity assay
In molecular biology, an annexin A5 affinity assay is a test to quantify the number of cells undergoing apoptosis. The assay uses the protein annexin A5 to tag apoptotic and dead cells and the numbers are then counted using either flow cytometry or a fluorescence microscope.The annexin a5 protein...
to detect cells that have expressed phosphatidylserine on the cell surface, a feature found in apoptosis
Apoptosis
Apoptosis is the process of programmed cell death that may occur in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation...
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.
Interactions
Annexin A5 has been shown to interactProtein-protein interaction
Protein–protein interactions occur when two or more proteins bind together, often to carry out their biological function. Many of the most important molecular processes in the cell such as DNA replication are carried out by large molecular machines that are built from a large number of protein...
with Kinase insert domain receptor
Kinase insert domain receptor
Kinase insert domain receptor also known as vascular endothelial growth factor receptor 2 is a VEGF receptor. KDR is the human gene encoding it. KDR has also been designated as CD309...
and Integrin, beta 5
Integrin, beta 5
Integrin beta-5 is a protein that in humans is encoded by the ITGB5 gene.-Interactions:Integrin, beta 5 has been shown to interact with PTK2, Annexin A5 and PAK4.-External links:* Info with links in the...
.