Structural basis for the in situ Ca(2+) sensitization of cardiac troponin C by positive feedback from force-generating myosin cross-bridges.

The in situ structural coupling between the cardiac troponin (cTn) Ca(2+)-sensitive regulatory switch (CRS) and strong myosin cross-bridges was investigated using Förster resonance energy transfer (FRET). The double cysteine mutant cTnC(T13C/N51C) was fluorescently labeled with the FRET pair 5-(iodoacetamidoethyl)aminonaphthelene-1-sulfonic acid (IAEDENS) and N-(4-dimethylamino-3,5-dinitrophenyl)maleimide (DDPM) and then incorporated into detergent skinned left ventricular papillary fiber bundles. Ca(2+) titrations of cTnC(T13C/N51C)AEDENS/DDPM-reconstituted fibers showed that the Ca(2+)-dependence of the opening of the N-domain of cTnC (N-cTnC) statistically matched the force-Ca(2+) relationship. N-cTnC opening still occurred steeply during Ca(2+) titrations in the presence of 1mM vanadate, but the maximal extent of ensemble-averaged N-cTnC opening and the Ca(2+)-sensitivity of the CRS were significantly reduced. At nanomolar, resting Ca(2+) levels, treatment with ADP·Mg in the absence of ATP caused a partial opening of N-cTnC. During subsequent Ca(2+) titrations in the presence of ADP·Mg and absence of ATP, further N-cTnC opening was stimulated as the CRS responded to Ca(2+) with increased Ca(2+)-sensitivity and reduced steepness. These findings supported our hypothesis here that strong cross-bridge interactions with the cardiac thin filament exert a Ca(2+)-sensitizing effect on the CRS by stabilizing the interaction between the exposed hydrophobic patch of N-cTnC and the switch region of cTnI.

[1]  R. Solaro Maintaining cooperation among cardiac myofilament proteins through thick and thin , 2009, The Journal of physiology.

[2]  W. Dong,et al.  Förster Resonance Energy Transfer Structural Kinetic Studies of Cardiac Thin Filament Deactivation* , 2009, The Journal of Biological Chemistry.

[3]  B. Sykes,et al.  An interplay between protein disorder and structure confers the Ca2+ regulation of striated muscle. , 2006, Journal of molecular biology.

[4]  R Craig,et al.  Crossbridge and tropomyosin positions observed in native, interacting thick and thin filaments. , 2001, Journal of molecular biology.

[5]  B. Slinker,et al.  Interaction between myosin heavy chain and troponin isoforms modulate cardiac myofiber contractile dynamics. , 2007, American journal of physiology. Regulatory, integrative and comparative physiology.

[6]  P. Fajer,et al.  Effects of calcium binding and the hypertrophic cardiomyopathy A8V mutation on the dynamic equilibrium between closed and open conformations of the regulatory N-domain of isolated cardiac troponin C. , 2013, Biochemistry.

[7]  H. Akaike Likelihood of a model and information criteria , 1981 .

[8]  B. Sykes,et al.  Binding of cardiac troponin-I147-163 induces a structural opening in human cardiac troponin-C. , 1999, Biochemistry.

[9]  D. Martyn,et al.  Cooperative cross-bridge activation of thin filaments contributes to the Frank-Starling mechanism in cardiac muscle. , 2009, Biophysical journal.

[10]  G. G. Stokes "J." , 1890, The New Yale Book of Quotations.

[11]  Richard L Moss,et al.  Myosin Crossbridge Activation of Cardiac Thin Filaments: Implications for Myocardial Function in Health and Disease , 2004, Circulation research.

[12]  W. Dong,et al.  Structural studies of interactions between cardiac troponin I and actin in regulated thin filament using Förster resonance energy transfer. , 2008, Biochemistry.

[13]  S. Ishiwata,et al.  Myosin light chain 2 modulates MgADP‐induced contraction in rabbit skeletal and bovine cardiac skinned muscle , 2002, The Journal of physiology.

[14]  David R. Anderson,et al.  Multimodel Inference , 2004 .

[15]  S. Lehman,et al.  Orthovanadate and orthophosphate inhibit muscle force via two different pathways of the myosin ATPase cycle. , 2011, Biophysical journal.

[16]  R Craig,et al.  Steric-model for activation of muscle thin filaments. , 1997, Journal of molecular biology.

[17]  Malcolm Irving,et al.  The molecular basis of the steep force–calcium relation in heart muscle , 2010, Journal of molecular and cellular cardiology.

[18]  John B. Shoven,et al.  I , Edinburgh Medical and Surgical Journal.

[19]  K. Gueth,et al.  Low Ca2+ impedes cross-bridge detachment in chemically skinned Taenia coli , 1982, Nature.

[20]  G. Guzman,et al.  Familial Hypertrophic Cardiomyopathy-linked Alterations in Ca2+ Binding of Human Cardiac Myosin Regulatory Light Chain Affect Cardiac Muscle Contraction* , 2004, Journal of Biological Chemistry.

[21]  W. Delano The PyMOL Molecular Graphics System , 2002 .

[22]  M. Saraste,et al.  FEBS Lett , 2000 .

[23]  A. Weber,et al.  Cooperation within actin filament in vertebrate skeletal muscle. , 1972, Nature: New biology.

[24]  D. Swartz,et al.  Influence of ADP on cross-bridge-dependent activation of myofibrillar thin filaments. , 2000, Biophysical journal.

[25]  W. Kerrick,et al.  Ca(2+) measurements in skinned cardiac fibers: effects of Mg(2+) on Ca(2+) activation of force and fiber ATPase. , 2000, Journal of applied physiology.

[26]  A. Straight,et al.  Blebbistatin, a myosin II inhibitor, is photoinactivated by blue light. , 2005, Biochemistry.

[27]  J. V. Van Eyk,et al.  Troponin replacement in permeabilized cardiac muscle Reversible extraction of troponin I by incubation with vanadate , 1992, FEBS letters.

[28]  J. Metzger,et al.  Myosin binding-induced cooperative activation of the thin filament in cardiac myocytes and skeletal muscle fibers. , 1995, Biophysical journal.

[29]  B. Sykes,et al.  Structural based insights into the role of troponin in cardiac muscle pathophysiology , 2004, Journal of Muscle Research & Cell Motility.

[30]  Svetlana B Tikunova,et al.  Effects of thin and thick filament proteins on calcium binding and exchange with cardiac troponin C. , 2007, Biophysical journal.

[31]  R. Solaro Sarcomere Control Mechanisms and the Dynamics of the Cardiac Cycle , 2010, Journal of biomedicine & biotechnology.

[32]  P. Rosevear,et al.  Effects of Troponin I Phosphorylation on Conformational Exchange in the Regulatory Domain of Cardiac Troponin C* , 1999, The Journal of Biological Chemistry.

[33]  H. Akaike A new look at the statistical model identification , 1974 .

[34]  S. Harrison,et al.  Hysteresis and the length dependence of calcium sensitivity in chemically skinned rat cardiac muscle. , 1988, The Journal of physiology.

[35]  Michael Regnier,et al.  Investigation of thin filament near‐neighbour regulatory unit interactions during force development in skinned cardiac and skeletal muscle , 2007, The Journal of physiology.

[36]  B. Pan,et al.  Calcium-binding properties of troponin C in detergent-skinned heart muscle fibers. , 1987, The Journal of biological chemistry.

[37]  J. V. Van Eyk,et al.  The C Terminus of Cardiac Troponin I Stabilizes the Ca2+-Activated State of Tropomyosin on Actin Filaments , 2010, Circulation research.

[38]  S. Lehrer The 3-state model of muscle regulation revisited: is a fourth state involved? , 2011, Journal of Muscle Research and Cell Motility.

[39]  G. Mocz Vanadate-mediated photocleavage of rabbit skeletal myosin. , 1989, European journal of biochemistry.

[40]  C. Cremo,et al.  UV-induced vanadate-dependent modification and cleavage of skeletal myosin subfragment 1 heavy chain. 1. Evidence for active site modification. , 1988, Biochemistry.

[41]  M. Reedy,et al.  Reverse actin sliding triggers strong myosin binding that moves tropomyosin , 2008, Proceedings of the National Academy of Sciences.

[42]  W. Dong,et al.  Structural Dynamics of C-domain of Cardiac Troponin I Protein in Reconstituted Thin Filament* , 2011, The Journal of Biological Chemistry.

[43]  W. Dong,et al.  Structural and kinetic effects of hypertrophic cardiomyopathy related mutations R146G/Q and R163W on the regulatory switching activity of rat cardiac troponin I. , 2013, Archives of biochemistry and biophysics.

[44]  J. Potter,et al.  Expanding the range of free calcium regulation in biological solutions. , 2005, Analytical biochemistry.

[45]  A. M. Gordon,et al.  Hysteresis in the force-calcium relation in muscle. , 1983, Science.

[46]  R. Solaro,et al.  A dominant role of cardiac molecular motors in the intrinsic regulation of ventricular ejection and relaxation. , 2007, Physiology.

[47]  M. Villain,et al.  Conformation of the Regulatory Domain of Cardiac Muscle Troponin C in Its Complex with Cardiac Troponin I* , 1999, The Journal of Biological Chemistry.

[48]  J. M. Robinson,et al.  Switching of troponin I: Ca(2+) and myosin-induced activation of heart muscle. , 2004, Journal of molecular biology.

[49]  R. Solaro,et al.  Calcium, thin filaments, and the integrative biology of cardiac contractility. , 2005, Annual review of physiology.

[50]  D. Allen,et al.  Calcium concentration in the myoplasm of skinned ferret ventricular muscle following changes in muscle length. , 1988, The Journal of physiology.

[51]  D. Root,et al.  Conformational selection during weak binding at the actin and myosin interface. , 2000, Biophysical journal.

[52]  B D Sykes,et al.  Calcium-induced structural transition in the regulatory domain of human cardiac troponin C. , 1997, Biochemistry.

[53]  W. Dong,et al.  Effects of PKA phosphorylation of cardiac troponin I and strong crossbridge on conformational transitions of the N-domain of cardiac troponin C in regulated thin filaments. , 2007, Biochemistry.

[54]  A. Muhlrad,et al.  Characterization of stable beryllium fluoride, aluminum fluoride, and vanadate containing myosin subfragment 1-nucleotide complexes. , 1992, Biochemistry.

[55]  G. T. Long,et al.  Photocleavage of myosin subfragment 1 by vanadate. , 1990, Biochemistry.

[56]  Malcolm Irving,et al.  Calcium‐ and myosin‐dependent changes in troponin structure during activation of heart muscle , 2009, The Journal of physiology.

[57]  J. M. Robinson,et al.  The cardiac Ca2+-sensitive regulatory switch, a system in dynamic equilibrium. , 2008, Biophysical journal.

[58]  Norio Fukuda,et al.  Titin and Troponin: Central Players in the Frank-Starling Mechanism of the Heart , 2009, Current cardiology reviews.

[59]  M. Geeves,et al.  Regulation of the interaction between actin and myosin subfragment 1: evidence for three states of the thin filament. , 1993, Biophysical journal.

[60]  P. Rosevear,et al.  Role of the acidic N′ region of cardiac troponin I in regulating myocardial function , 2008, FASEB journal : official publication of the Federation of American Societies for Experimental Biology.

[61]  I. Ringel,et al.  Effect of actin, ATP, phosphates, and pH on vanadate-induced photocleavage of myosin subfragment 1. , 1991, Biochemistry.

[62]  David D. Thomas,et al.  Structural dynamics of actin during active interaction with myosin: different effects of weakly and strongly bound myosin heads. , 2004, Biochemistry.