The role of tropomyosin domains in cooperative activation of the actin-myosin interaction

Yusuke Oguchi, Junji Ishizuka, Sarah E. Hitchcock-Degregori, Shin'Ichi Ishiwata, Masataka Kawai*

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    21 Citations (Scopus)


    To establish α-tropomyosin (Tm)'s structure-function relationships in cooperative regulation of muscle contraction, thin filaments were reconstituted with a variety of Tm mutants (Δ2Tm, Δ3Tm, Δ6Tm, P2sTm, P3sTm, P2P3sTm, P1P5Tm, and wtTm), and force and sliding velocity of the thin filament were studied using an in vitro motility assay. In the case of deletion mutants, Δ indicates which of the quasi-equivalent repeats in Tm was deleted. In the case of period (P) mutants, an Ala cluster was introduced into the indicated period to strengthen the Tm-actin interaction. In P1P5Tm, the N-terminal half of period 5 was substituted with that of period 1 to test the quasi-equivalence of these two Tm periods. The reconstitution included bovine cardiac troponin. Deletion studies revealed that period 3 is important for the positive cooperative effect of Tm on actin filament regulation and that period 2 also contributes to this effect at low ionic strength, but to a lesser degree. Furthermore, Tm with one extra Ala cluster at period 2 (P2s) or period 3 (P3s) did not increase force or velocity, whereas Tm with two extra Ala clusters (P2P3s) increased both force and velocity, demonstrating interaction between these periods. Most mutants did not move in the absence of Ca 2+. Notable exceptions were Δ6Tm and P1P5Tm, which moved near at the full velocity, but with reduced force, which indicate impaired relaxation. These results are consistent with the mechanism that the Tm-actin interaction cooperatively affects actin to result in generation of greater force and velocity.

    Original languageEnglish
    Pages (from-to)667-680
    Number of pages14
    JournalJournal of Molecular Biology
    Issue number5
    Publication statusPublished - 2011 Dec 16


    • actin
    • force and velocity
    • in vitro motility
    • mutant
    • optical tweezers

    ASJC Scopus subject areas

    • Molecular Biology


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