Effects of Thin and Thick Filament Proteins on Calcium Binding and Exchange With Cardiac Troponin C

Biophys J. 2007 May 1;92(9):3195-206. doi: 10.1529/biophysj.106.095406. Epub 2007 Feb 9.

Abstract

Understanding the effects of thin and thick filament proteins on the kinetics of Ca(2+) exchange with cardiac troponin C is essential to elucidating the Ca(2+)-dependent mechanisms controlling cardiac muscle contraction and relaxation. Unlike labeling of the endogenous Cys-84, labeling of cardiac troponin C at a novel engineered Cys-53 with 2-(4'-iodoacetamidoanilo)napthalene-6-sulfonic acid allowed us to accurately measure the rate of calcium dissociation from the regulatory domain of troponin C upon incorporation into the troponin complex. Neither tropomyosin nor actin alone affected the Ca(2+) binding properties of the troponin complex. However, addition of actin-tropomyosin to the troponin complex decreased the Ca(2+) sensitivity ( approximately 7.4-fold) and accelerated the rate of Ca(2+) dissociation from the regulatory domain of troponin C ( approximately 2.5-fold). Subsequent addition of myosin S1 to the reconstituted thin filaments (actin-tropomyosin-troponin) increased the Ca(2+) sensitivity ( approximately 6.2-fold) and decreased the rate of Ca(2+) dissociation from the regulatory domain of troponin C ( approximately 8.1-fold), which was completely reversed by ATP. Consistent with physiological data, replacement of cardiac troponin I with slow skeletal troponin I led to higher Ca(2+) sensitivities and slower Ca(2+) dissociation rates from troponin C in all the systems studied. Thus, both thin and thick filament proteins influence the ability of cardiac troponin C to sense and respond to Ca(2+). These results imply that both cross-bridge kinetics and Ca(2+) dissociation from troponin C work together to modulate the rate of cardiac muscle relaxation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / metabolism*
  • Animals
  • Calcium / metabolism*
  • Cells, Cultured
  • Male
  • Myocardial Contraction / physiology*
  • Myocytes, Cardiac / metabolism*
  • Myosins / metabolism*
  • Protein Binding
  • Rats
  • Sarcomeres / physiology*
  • Troponin C / metabolism*

Substances

  • Actins
  • Troponin C
  • Myosins
  • Calcium