Gap junction proteins, also known as connexins, are integral membrane proteins that form specialized channels between adjacent cells. These channels, called gap junctions, allow for the direct exchange of small molecules, ions, and electrical signals between cells. Gap junction proteins play a crucial role in cell communication and the synchronization of physiological processes.
Gap junction proteins are typically composed of six subunits, known as connexin proteins, which come together to form a hexameric structure. Each connexin possesses four transmembrane domains, two extracellular loops, a cytoplasmic loop, and a cytoplasmic amino and carboxyl terminus. The hexamers of connexin proteins align in the plasma membrane of adjacent cells to form a pore-like structure, creating a direct communication pathway between the cytoplasm of the connected cells.
These proteins are widely distributed in various tissues and cell types, including nerve cells, cardiac muscle cells, epithelial cells, and astrocytes. They play a prominent role in the coordination of cellular activities such as the propagation of electrical impulses, cell growth regulation, differentiation, and tissue development. The selective permeability of gap junction channels is critically regulated, allowing for the passage of specific molecules, ions, and second messengers based on size and charge considerations.
Disruptions or mutations in gap junction proteins can lead to several pathological conditions, including cardiovascular diseases, deafness, skin disorders, and certain forms of cancer. Studying the structure, function, and regulation of these proteins is essential for understanding their roles in physiology and pathology and may provide potential therapeutic targets for treating associated diseases.
