Effect of the Structure of the N Terminus of Tropomyosin on Tropomodulin Function

Alla S. Kostyukova, Sarah E. Hitchcock-DeGregori

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55 Scopus citations

Abstract

Tropomodulins (Tmod) bind to the N terminus of tropomyosin and cap the pointed end of actin filaments. Tropomyosin alone also inhibits the rate of actin depolymerization at the pointed end of filaments. Here we have defined 1) the structural requirements of the N terminus of tropomyosin important for regulating the pointed end alone and with erythrocyte Tmod (Tmod1), and 2) the Tmod1 subdomains required for binding to tropomyosin and for regulating the pointed end. Changes in pyrene-actin fluorescence during polymerization and depolymerization were measured with actin filaments blocked at the barbed end with gelsolin. Three tropomyosin isoforms differently influence pointed end dynamics. Recombinant TM5a, a short non-muscle α-tropomyosin, inhibited depolymerization. Recombinant (unacetylated) TM2 and N-acetylated striated muscle TM (stTM), long α-tropomyosin isoforms with the same N-terminal sequence, different from TM5a, also inhibited depolymerization but were less effective than TM5a. All blocked the pointed end with Tmod1 in the order of effectiveness TM5a >stTM >TM2, showing the importance of the N-terminal sequence and modification. Tmod1-(1-344), lacking the C-terminal 15 residues, did not nucleate polymerization but blocked the pointed end with all three tropomyosin isoforms as does a shorter fragment, Tmod1-(1-92), lacking the C-terminal "capping" domain though higher concentrations were required. An even shorter fragment, Tmod1-(1-48), bound tropomyosin but did not influence actin filament elongation. Tropomyosin-Tmod may function to locally regulate cytoskeletal dynamics in cells by stabilizing actin filaments.

Original languageEnglish (US)
Pages (from-to)5066-5071
Number of pages6
JournalJournal of Biological Chemistry
Volume279
Issue number7
DOIs
StatePublished - Feb 13 2004

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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