Tropomyosin alpha-1 chain is aprotein that in humans is encoded by theTPM1gene.[5] This gene is a member of the tropomyosin (Tm) family of highly conserved, widely distributed actin-binding proteins involved in the contractile system of striated and smooth muscles and the cytoskeleton of non-muscle cells.
Tm is a 32.7 kDa protein composed of 284 amino acids.[6] Tm is a flexible protein homodimer or heterodimer composed of twoalpha-helical chains, which adopt a bentcoiled coil conformation to wrap around the sevenactin molecules in a functional unit of muscle.[7] It is polymerized end to end along the two grooves of actin filaments and provides stability to the filaments. Human striated muscles express protein from theTPM1 (α-Tm),TPM2 (β-Tm) andTPM3 (γ-Tm) genes, with α-Tm being the predominant isoform in striated muscle. In human cardiac muscle the ratio of α-Tm toβ-Tm is roughly 5:1.[8]
Tm functions in association with the troponin complex to regulate the calcium-dependent interaction ofactin andmyosin during muscle contraction. Tm molecules are arranged head-to-tail along the actin thin filament, and are a key component in cooperative activation of muscle. A three state model has been proposed by McKillop and Geeves,[9] which describes the positions of Tm during a cardiac cycle. The blocked (B) state occurs in diastole when intracellular calcium is low and Tm blocks themyosin binding site on actin. The closed (C) state is when Tm is positioned on the inner groove ofactin; in this statemyosin is in a "cocked" position where heads are weakly bound and not generating force. Themyosin binding (M) state is when Tm is further displaced fromactin bymyosin crossbridges that are strongly-bound and actively generating force. In addition to actin, Tm bindstroponin T (TnT). TnT tethers the region of head-to-tail overlap of subsequent Tm molecules toactin.
^"Human PubMed Reference:".National Center for Biotechnology Information, U.S. National Library of Medicine.
^"Mouse PubMed Reference:".National Center for Biotechnology Information, U.S. National Library of Medicine.
^Mogensen J, Kruse TA, Børglum AD (Jun 1999). "Refined localization of the human alpha-tropomyosin gene (TPM1) by genetic mapping".Cytogenetics and Cell Genetics.84 (1–2):35–36.doi:10.1159/000015207.PMID10343096.S2CID84901339.
^"Protein Information".Cardiac Organellar Protein Atlas Knowledgebase (COPaKB). Archived from the original on September 24, 2015. Retrieved25 May 2023.
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Gunning P, Weinberger R, Jeffrey P (April 1997). "Actin and tropomyosin isoforms in morphogenesis".Anatomy and Embryology.195 (4):311–315.doi:10.1007/s004290050050.PMID9108196.S2CID9692297.
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Mische SM, Manjula BN, Fischetti VA (February 1987). "Relation of streptococcal M protein with human and rabbit tropomyosin: the complete amino acid sequence of human cardiac alpha tropomyosin, a highly conserved contractile protein".Biochemical and Biophysical Research Communications.142 (3):813–818.Bibcode:1987BBRC..142..813M.doi:10.1016/0006-291X(87)91486-0.PMID3548719.
