Annexins

Annexins

Annexins are a family of proteins that play a crucial role in various cellular processes, including membrane trafficking, inflammation, and cell signaling. These proteins are characterized by their ability to bind to phospholipid membranes in a calcium-dependent manner. Annexins are found in a wide range of organisms, from humans to plants, and are involved in numerous physiological and pathological processes.

Structure

Annexins are typically composed of a conserved core domain and a variable N-terminal region. The core domain consists of four or eight repeats, each approximately 70 amino acids long, which form a compact, alpha-helical structure. This domain is responsible for the calcium-dependent binding to phospholipids. The N-terminal region varies among different annexins and is thought to confer specific functional properties to each annexin.

Function

Annexins are involved in a variety of cellular functions, including:

• Membrane trafficking: Annexins play a role in the transport of vesicles within cells, particularly in the endocytic and exocytic pathways.
• Inflammation: Certain annexins, such as Annexin A1, have anti-inflammatory properties and are involved in the resolution of inflammation.
• Cell signaling: Annexins can interact with other proteins and participate in signaling pathways that regulate cell growth, apoptosis, and differentiation.
• Calcium homeostasis: By binding to calcium ions, annexins help regulate intracellular calcium levels, which is crucial for various cellular processes.

Clinical Significance

Annexins have been implicated in several diseases, including cancer, cardiovascular diseases, and autoimmune disorders. For example, altered expression of annexins has been observed in various types of cancer, suggesting a role in tumor progression and metastasis. Annexin A5 is used in clinical settings as a marker for apoptosis, as it binds to phosphatidylserine, a phospholipid that is externalized on the surface of apoptotic cells.

Research and Applications

Research on annexins continues to uncover their diverse roles in health and disease. Annexins are being explored as potential therapeutic targets and diagnostic markers. For instance, annexin-based imaging techniques are being developed to detect apoptotic cells in vivo, which could have applications in cancer diagnosis and treatment monitoring.

Also see

• Phospholipids
• Calcium signaling
• Apoptosis
• Inflammation