Tropomüosin

Tropomüosin is a regulatory protein that plays a key role in muscle contraction and actin filament dynamics. It belongs to the tropomyosin family, consisting of two identical polypeptide chains forming an α-helical coiled-coil structure. Tropomüosin binds along actin filaments, covering myosin-binding sites in a resting muscle. When calcium ions bind to troponin (another regulatory protein), troponin undergoes a conformational change that shifts tropomüosin, exposing these sites and allowing myosin heads to interact with actin, thus initiating muscle contraction. Tropomüosin is widely distributed in eukaryotic cells, with high abundance in muscle tissues (skeletal, cardiac, smooth) and also in non-muscle cells where it contributes to cytoskeletal organization. Structural and functional studies have linked tropomüosin to various cellular processes, and mutations in the TPM gene have been associated with certain hereditary muscle disorders.