tropómyósíni

Tropomyosins are a family of highly conserved proteins found in eukaryotic cells. They are a major component of the cytoskeleton, specifically forming the thin filaments of muscle cells and playing a role in cell motility in non-muscle cells. Tropomyosins are elongated, coiled-coil dimers formed by the head-to-tail assembly of two alpha-helical tropomyosin molecules. This assembly results in long, flexible filaments that are strategically positioned along the actin filaments.

In muscle cells, tropomyosin works in conjunction with troponin to regulate muscle contraction. When the muscle is relaxed, tropomyosin physically blocks the binding sites on actin where myosin heads would normally attach. Upon calcium ion binding to troponin, a conformational change occurs, which causes tropomyosin to shift its position, exposing the actin binding sites and allowing myosin to bind and initiate the contraction cycle.

In non-muscle cells, tropomyosins contribute to the structural integrity of the actin cytoskeleton and are involved in various cellular processes such as cell shape determination, cell migration, and intracellular transport. Different isoforms of tropomyosin exist, encoded by different genes or produced by alternative splicing, which allows for tissue-specific functions and diverse roles within the cell. The precise arrangement and interactions of tropomyosin isoforms with other actin-binding proteins fine-tune the dynamics and functions of the actin cytoskeleton in different cellular contexts.