Tropomodulin (TMOD) is a protein which binds and caps the minus end of actin (the "pointed" end), regulating the length of actin filaments in muscle and non-muscle cells.
The protein functions by physically blocking the spontaneous dissociation of ADP-bound actin monomers from the minus end of the actin fibre. This, along with plus end capping proteins, such as capZ stabilise the structure of the actin filament. End capping is particularly important when long-lived actin filaments are necessary, for example: in myofibrils. Inhibition of tropomodulin capping activity leads to dramatic increase in thin filament length from its pointed end.
Actin filaments have two differing ends where one is the fast-acting barbed end and the other is the slow growing pointed end. Since TMOD binds to the pointed end of actin it is essential in cell morphology, cell movement, and muscle contraction. TMOD has been identified as an erythrocyte with 359 amino acids and it is a globular protein. When tropomyosin is not present Tropomodulin also assists in partially inhibiting elongation and depolymerization at the pointed filament ends. The N-terminal of Tropomodulin is rod shaped. This portion then binds to the N-terminal part of the two tropomyosin that are on the opposite part of the actin filaments in the muscle and nonmuscle cells. TMOD is able to have high-affinity binding through low-affinity interactions because of its ability to control subunit exchange of the pointed end of the actin filaments. When looking at epithelial cells Tropomodulin sustains F-actin in the lateral cell membranes and the adherens junction. Tropomodulin binds exclusively to the pointed filament ends and not to actin monomers or alongside actin filaments. Tropomodulin is a 40-kD tropomyosin-binding protein that was originally isolated from the red blood cell membrane skeleton. Tropomodulin is associated with Leiomodin as homologous proteins because both proteins play a role in muscle sarcomere thin filament formation and maintenance. An ortholog that is identified with TMOD and structurally similar  is UNC-94. Where the UNC-94 protein is capping on the minus end of the actin filament. This protein like TMOD depends on the presence of tropomyosin in order to function properly.
Genes.
The TMOD genes are important for cell morphology, cell movement, and muscle contraction. There are 4 identified Tropomodulin genes identified in humans: TMOD1, TMOD2, TMOD3, and TMOD4. The 4 identified genes are also recognized as Isoforms. There are also known orthologs of these isoforms in mice. Known tropomodulin homologs have been identified in flies (Drosophila), worms (C.elegans), rats, chicks, and mice. The TMOD genes are expressed at different levels in human tissue. The different levels can be identified as: the first level is heart and skeletal muscle, then the next level is found  in brain, lung, and pancreas, then the last level in placenta, liver, and kidney. Using the lab technique PCR TMOD gene was isolated and identified to have a total of 9 exons, allowing for the assumption that alternative promoters for tissue-specific expression and regulation. TMOD1, TMOD3, and TMOD4 are the only isoforms that are found in muscles. TMOD2 is the only identified isoform that is only found in the brain and not in any muscles like the other isoforms. The two isoforms that are associated with neurons are TMOD1 and TMOD2. The functions of each isoform can vary depending on the location of the Tropomyosin and actin filaments. Since the TMOD isoforms can influence stability of skeleton cells and regulate actin it can then be seen as essential for embryonic development.
References.
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