Annexin
Annexin is a family of proteins that are characterized by their ability to bind to phospholipids in a calcium-dependent manner. They are found in a wide variety of organisms, including humans, and play important roles in various cellular processes such as cell division, signal transduction, and apoptosis.
Structure[edit]
Annexins are typically composed of four or eight similar domains, each of which contains a type II calcium binding site. The core of each domain is formed by five alpha-helices, while the calcium binding site is located at the end of the fifth helix. The domains are arranged in a circular fashion, creating a concave side that is responsible for phospholipid binding.
Function[edit]
The primary function of annexins is to bind to phospholipids in a calcium-dependent manner. This allows them to participate in a variety of cellular processes. For example, during cell division, annexins help to form the contractile ring that separates the two daughter cells. In signal transduction, they can act as ion channels or receptors, transmitting signals from the outside of the cell to the inside. In apoptosis, they can help to mediate the process of cell death.
Clinical significance[edit]
Due to their involvement in a variety of cellular processes, annexins have been implicated in a number of diseases. For example, mutations in the gene for annexin A5 have been associated with recurrent miscarriage, while overexpression of annexin A2 has been linked to cancer.
