Tropomyosin requires an intact N-terminal coiled coil to interact with tropomodulin

Biophys J. 2002 May;82(5):2580-91. doi: 10.1016/S0006-3495(02)75600-2.

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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acetylation
  • Actins / chemistry
  • Actins / metabolism
  • Amino Acid Sequence
  • Binding Sites
  • Carrier Proteins / metabolism*
  • Circular Dichroism
  • Humans
  • Kinetics
  • Microfilament Proteins*
  • Models, Molecular
  • Molecular Sequence Data
  • Myopathies, Nemaline / genetics
  • Myopathies, Nemaline / pathology
  • Peptide Fragments / chemistry
  • Peptide Fragments / metabolism
  • Protein Conformation
  • Protein Denaturation
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / metabolism
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Thermodynamics
  • Tropomodulin
  • Tropomyosin / chemistry*
  • Tropomyosin / metabolism*

Substances

  • Actins
  • Carrier Proteins
  • Microfilament Proteins
  • Peptide Fragments
  • Recombinant Fusion Proteins
  • TMOD1 protein, human
  • Tropomodulin
  • Tropomyosin