Tropomyosins are a family of highly conserved actin-binding proteins. They not only bind to actin, but also help to regulate myosin's interaction with actin's thin filaments. In striated muscle, tropomyosin forms a complex with troponin which makes the regulation of vertebrate striated muscle contraction calcium (Ca2+)-sensitive.
Alpha-tropomyosin is a two-stranded alpha-helical coiled coil that has a highly conserved N-terminal region critical for the function of striated muscle tropomyosin. This region is identical in both Drosophila and rabbit. Removal of any amino-acid residues in the N-terminus results in loss of actin affinity and the presence of troponin.
The peptide shown here, TMZip, is a chimeric model representing the N-terminus of alpha-tropomyosin. It is a dimer consisting of 2 chains, each which is 32 amino-acid residues long. Residues 1-14 are from the N-terminal residues 1-14 of rabbit alpha-tropomyosin. Residues 15-32 are from the C-terminal residues 264-281 of Saccharomyces cerevisiae (yeast) transcription factor GCN4.
The first nine residues are proposed to bind to the carboxyl-terminal nine residues to form the "overlap" region between successive Tropomyosins, which bind along the actin filament. The side chains of these residues are shown in purple.
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