Tropomyosin is a two-stranded alpha-helical, coiled coil protein found in actin-based cytoskeletons. All organisms contain organelles that provide physical integrity to their cells. These type of organelles are collectively known as the cytoskeleton, and one of the most ancient systems is based on filamentous polymers of the protein actin. A polymer of a second protein, tropomyosin, is an integral part of most actin filaments in animals.
Tropomyosins are a large family of integral components of actin filaments that play a critical role in regulating the function of actin filaments in both muscle and nonmuscle cells. These proteins consist of rod-shaped coiled-coil hetero- or homo-dimers that lie along the α-helical groove of most actin filaments. Interaction occurs along the length of the actin filament, with dimers aligning in a head-to-tail fashion.
Tropomyosins are often categorised into two groups, muscle tropomyosin isoforms and non muscle tropomyosin isoforms. Muscle tropomyosin isoforms are involved in regulating interactions between actin and myosin in the muscle sarcomere and play a pivotal role in regulated muscle contraction. Non Muscle tropomyosin isoforms function in all cells, both muscle and nonmuscle cells, and are involved in a range of cellular pathways that control and regulate the cell’s cytoskeleton and other key cellular functions.
The actin filament system that is involved in regulating these cellular pathways is more complex than the actin filament systems that regulates muscle contraction. The contractile system relies upon 4 actin filament isoforms and 5 tropomyosin isoforms,whereas the actin filament system of the cytoskeleton uses two actin filament isoforms and over 40 tropomyosin isoforms.