tropomyosiinin

Tropomyosiinin, known in English as tropomyosin, is a family of elongated coiled-coil proteins that bind along actin filaments. In muscle and non-muscle cells, tropomyosin stabilizes actin filaments and modulates interactions with other actin-binding proteins. In striated muscle, tropomyosin lies along the thin filament and, together with the troponin complex, regulates contraction. When intracellular calcium is low, troponin I and tropomyosin block myosin-binding sites on actin, preventing cross-bridge cycling. Elevation of Ca2+ leads to binding of calcium by troponin C, causing a conformational change that shifts tropomyosin away from the binding sites and permits myosin attachment and muscle contraction.

Tropomyosin is a parallel coiled-coil dimer, with two α-helical chains wrapping around each other. It forms continuous polymers along actin filaments by head-to-tail interactions. Several TPM genes (TPM1, TPM2, TPM3, TPM4) encode tissue-specific isoforms, and alternative splicing yields multiple variants. Isoform composition determines filament properties and interactions with myosin and other actin-binding proteins, contributing to differences among skeletal, cardiac, and smooth muscle, as well as non-muscle cells.

Beyond muscle, non-muscle tropomyosins help stabilize actin filaments, modulate filament dynamics, and participate in processes such as cell polarity, vesicle trafficking, and cytoskeletal remodeling. Tropomyosin interacts with numerous actin-associated proteins and can affect motor protein activity.

Mutations in tropomyosin genes can cause congenital myopathies and cardiomyopathies, including certain forms of distal arthrogryposis and fiber-type disproportion. Abnormal tropomyosin expression or misregulation has also been observed in some cancers and cytoskeletal disorders.