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The C-terminus of troponin T is essential for maintaining the inactive state of regulated actin

Andrew J Franklin1, Tamatha Baxley, Tomoyoshi Kobayashi

  • 1Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, North Carolina, USA.

Biophysical Journal
|June 21, 2012
PubMed

Insights

Cardiac troponin T (TnT) mutations disrupt muscle contraction regulation. This study reveals TnT

Area of Science:

  • Muscle physiology
  • Biochemistry
  • Molecular biology

Background:

  • Striated muscle contraction relies on actin-binding proteins tropomyosin and troponin.
  • Dysfunctional troponin T (TnT) is linked to myopathies and cardiomyopathies.
  • A specific deletion (Δ14) in cardiac TnT causes hypertrophic cardiomyopathy.

Purpose of the Study:

  • To investigate the role of the C-terminus of cardiac troponin T in regulating actin's inactive state.
  • To determine if Δ14 TnT-containing actin filaments can transition to the inactive state.

Main Methods:

  • Biochemical assays measuring ATPase activity of regulated actin filaments.
  • Fluorescence spectroscopy using acrylodan-labeled tropomyosin to monitor state transitions.
  • Experiments involving modified troponin I (TnI) to probe the inactive state.

Main Results:

  • Actin filaments with Δ14 TnT exhibit elevated ATPase activity without calcium (Ca2+), indicating a shift towards activation.
  • These filaments fail to enter the inactive state, as evidenced by the lack of fluorescence changes upon S1-ATP dissociation.
  • Modifying troponin I to favor the inactive state did not restore the characteristic fluorescence change in Δ14 TnT filaments.

Conclusions:

  • Troponin T plays a critical, previously unrecognized role in establishing the inactive state of the actin-myosin complex.
  • The C-terminus of TnT is essential for the proper formation and stability of the inactive state in muscle contraction regulation.

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