Tropomyosin is a two-stranded alpha-helical, coiled coil protein found in many animal and fungal cells. In animals, it is an important component of the muscular system which works in conjunction with troponin to regulate muscle contraction. It is present in smooth and striated muscle tissues, which can be found in various organs and body systems, including the heart, blood vessels, respiratory system, and digestive system. In fungi, tropomyosin is found in cell walls and helps maintain the structural integrity of cells.

Tropomyosin is found in other eukaryotes too, but not in plants. Overall, tropomyosin is an important protein that plays a vital role in the proper functioning of many different organisms.

The cytoskeleton, an organelle system responsible for providing physical integrity to cells, includes actin filaments. Tropomyosins, a large family of proteins, are integral components of actin filaments in animals and play a critical role in regulating their function in muscle and nonmuscle cells. Tropomyosins can be categorized into muscle and nonmuscle isoforms. Higher eukaryotes, like humans, express more protein isoforms than genes through alternative splicing. In mammals, four genes generate over 40 different tropomyosin isoforms, which are highly regulated and involved in numerous cellular processes. Tropomyosin isoform sorting is complex and highly regulated, influenced by mRNA sorting and actin isoform composition of microfilaments. Studies have shown that tropomyosins perform essential functions in a diverse range of species, and isoforms are not functionally redundant.

Isoforms of tropomyosins are essential for various cellular functions in species ranging from yeast to complex mammals. TPM1 and TPM2 genes display overlapping functions, but TPM2 cannot fully compensate for the loss of TPM1, suggesting unique functions for TPM1. Tropomyosin isoforms influence the binding of actin-binding proteins to actin filaments and participate in various cellular functions, including skeletal muscle contraction, smooth muscle contraction, cytoskeleton function, and diseases such as cancer and autoimmunity. The expression and complement of tropomyosin isoforms are integral to cancer and cancer progression, with cells becoming more reliant on low molecular weight tropomyosins as high molecular weight tropomyosins disappear with increasing malignancy. Tropomyosin isoforms have also been implicated in autoimmune diseases and muscle disorders.