title: Tropomyosin requires an intact N-terminal coiled coil to interact with tropomodulin.
abstract: Tropomodulins (Tmods) are tropomyosin (TM) binding proteins that bind to the pointed end of actin filaments and modulate thin filament dynamics. They bind to the N termini of both "long" TMs (with the N terminus encoded by exon 1a of the alpha-TM gene) and "short" nonmuscle TMs (with the N terminus encoded by exon 1b). In this present study, circular dichroism was used to study the interaction of two designed chimeric proteins, AcTM1aZip and AcTM1bZip, containing the N terminus of a long or a short TM, respectively, with protein fragments containing residues 1 to 130 of erythrocyte or skeletal muscle Tmod. The binding of either TMZip causes similar conformational changes in both Tmod fragments promoting increases in both alpha-helix and beta-structure, although they differ in binding affinity. The circular dichroism changes in the Tmod upon binding and modeling of the Tmod sequences suggest that the interface between TM and Tmod includes a three- or four-stranded coiled coil. An intact coiled coil at the N terminus of the TMs is essential for Tmod binding, as modifications that disrupt the N-terminal helix, such as removal of the N-terminal acetyl group from AcTM1aZip or striated muscle alpha-TM, or introduction of a mutation that causes nemaline myopathy, Met-8-Arg, into AcTM1aZip destroyed Tmod binding.
authors.affiliation: University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854-5635, USA. greenfie@rwja.umdnj.edu
authors.forename: Norma J
authors.initials: NJ
authors.lastname: Greenfield
authors.forename: Velia M
authors.initials: VM
authors.lastname: Fowler
mesh_terms: D000107:Acetylation; D000199:Actins / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism*; D002942:Circular Dichroism; D006801:Humans; D007700:Kinetics; D008840:Microfilament Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017696:Myopathies, Nemaline / Q000235:genetics / Q000473:pathology; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D011489:Protein Denaturation; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013816:Thermodynamics; D051348:Tropomodulin; D014335:Tropomyosin / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D000199:Actins; D002352:Carrier Proteins; D008840:Microfilament Proteins; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; C495829:TMOD1 protein, human; D051348:Tropomodulin; D014335:Tropomyosin