Annexins are a group of proteins that were first discovered in the 1970s and are primarily found in eukaryotic cells. They are characterized by their ability to bind and interact with cell membranes in a calcium-dependent manner. The name "annexin" is derived from their tendency to associate with or "annex" membranes.
These proteins are highly conserved across various species, including animals, plants, and fungi, indicating their fundamental role in cellular function. Annexins are involved in a wide range of biological processes, such as membrane repair, vesicle trafficking, apoptosis (programmed cell death), cell division, and signal transduction.
Structurally, annexins possess a globular core domain composed of repeated four-helix bundles, which can bind to negatively charged phospholipids on the inner leaflet of the plasma membrane. This binding is mediated by calcium ions, which induce conformational changes in annexins, allowing them to interact with the membrane.
Several isoforms of annexins exist, each with specific functions and tissue distributions. For instance, Annexin A1 is involved in inflammation regulation, Annexin A2 participates in cellular adhesion and migration, and Annexin A5 has anticoagulant properties. These proteins have also been implicated in various diseases, including cancer, cardiovascular disorders, and neurodegenerative conditions.
Overall, annexins play critical roles in cellular physiology, allowing for the proper functioning and organization of cells. Further research into the diverse functions and mechanisms of annexins may lead to new insights into cellular processes and potential therapeutic targets.
