tropómýósín

Tropomyosin is a protein found in muscle and other cells. In muscle cells, it exists as a coiled-coil dimer that lies along the actin filaments. Tropomyosin plays a crucial role in the regulation of muscle contraction by controlling the interaction between actin and myosin.

In its relaxed state, tropomyosin partially covers the myosin-binding sites on actin filaments. This prevents myosin from binding to actin, and thus prevents muscle contraction. When a muscle cell receives a signal to contract, calcium ions are released into the cytoplasm. These calcium ions bind to troponin, a complex of proteins associated with tropomyosin. This binding causes a conformational change in troponin, which in turn shifts tropomyosin away from the myosin-binding sites on actin. With the binding sites now exposed, myosin can bind to actin, initiating the sliding filament mechanism that leads to muscle contraction.

Tropomyosin is composed of two alpha-helical subunits wound around each other. Different isoforms of tropomyosin exist, which are expressed in a tissue-specific manner, contributing to the diverse functional properties of various muscle types and non-muscle cells. In addition to its role in muscle, tropomyosin is also involved in cellular processes such as cell shape, cell adhesion, and intracellular transport in non-muscle cells. Mutations in tropomyosin genes are associated with several human diseases, including cardiomyopathies and nemaline myopathy.