Tropomyosin requires an intact N-terminal coiled coil to interact with tropomodulin.
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.
Greenfield
Norma J
NJ
University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854-5635, USA. greenfie@rwja.umdnj.edu
Fowler
Velia M
VM
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*
D000199:Actins; D002352:Carrier Proteins; D008840:Microfilament Proteins; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; C495829:TMOD1 protein, human; D051348:Tropomodulin; D014335:Tropomyosin