Cardiomyopathy-Related Mutations in Cardiac Troponin C, L29Q and G159D, Have Divergent Effects on Rat Cardiac Myofiber Contractile Dynamics

Previous studies of cardiomyopathy-related mutations in cardiac troponin C (cTnC)—L29Q and G159D—have shown diverse findings. The link between such mutant effects and their divergent impact on cardiac phenotypes has remained elusive due to lack of studies on contractile dynamics. We hypothesized that a cTnC mutant-induced change in the thin filament will affect global myofilament mechanodynamics because of the interactions of thin filament kinetics with bothCa2+binding and crossbridge (XB) cycling kinetics. We measured pCa-tension relationship and contractile dynamics in detergent-skinned rat cardiac papillary muscle fibers reconstituted with the recombinant wild-type rat cTnC (cTnCWT),cTnCL29Q, andcTnCG159Dmutants.cTnCL29Qfibers demonstrated a significant decrease inCa2+sensitivity, butcTnCG159Dfibers did not. Both mutants had no effect onCa2+-activated maximal tension. The rate of XB recruitment dynamics increased incTnCL29Q(26%) andcTnCG159D(25%) fibers. The rate of XB distortion dynamics increased incTnCG159Dfibers (15%). Thus, thecTnCL29Qmutant modulates the equilibrium between the non-cycling and cycling pool of XB by affecting theon/offkinetics of the regulatory units (Tropomyosin-Troponin); whereas, thecTnCG159Dmutant increases XB cycling rate. Different effects on contractile dynamics may offer clue regarding howcTnCL29QandcTnCG159Dcause divergent effects on cardiac phenotypes.

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Binding of Calcium and Magnesium to Cardiac Troponin C

10.1101/2020.06.14.150854 ◽

2020 ◽

Author(s):

K Rayani ◽

JT Seffernick ◽

YA Li ◽

JP Davis ◽

AM Spuches ◽

...

Keyword(s):

Conformational Changes ◽

Cardiac Troponin ◽

Thin Filament ◽

Force Production ◽

Troponin C ◽

Titration Calorimetry ◽

Wild Type ◽

Cardiac Troponin C ◽

Functional Consequences ◽

Calcium And Magnesium

AbstractCardiac troponin C (cTnC) is the Ca2+-sensing component of the thin filament. It contains structural sites (III/IV) which bind both Ca2+ and Mg2+, and a regulatory site (II) that has been thought to bind only Ca2+. The latter binding initiates a series of conformational changes that culminate in force production.We have quantified the interaction between site II and Ca2+/Mg2+ through Isothermal Titration Calorimetry and Thermodynamic Integration simulations. Direct and competitive binding titrations using wild type and a double mutant that significantly reduces binding to site II demonstrated that physiologically relevant concentrations of both Ca2+/Mg2+ interact with the same locus. Cytosolic free Mg2+ (~1 mM) could occupy a significant population of available site II, as this concentration of Mg2+ decreased the affinity for Ca2+ 1.4-fold.Interaction of Mg2+ with site II of cTnC likely has important functional consequences for the heart at baseline and in diseased states which decrease or increase availability of Mg2+ such as secondary hyperparathyroidism or ischemia, respectively.

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Altered Ca2+ dependence of tension development in skinned skeletal muscle fibers following modification of troponin by partial substitution with cardiac troponin C.

Journal of Biological Chemistry ◽

10.1016/s0021-9258(17)38497-1 ◽

1986 ◽

Vol 261 (13) ◽

pp. 6096-6099 ◽

Cited By ~ 6

Author(s):

R L Moss ◽

M R Lauer ◽

G G Giulian ◽

M L Greaser

Keyword(s):

Skeletal Muscle ◽

Cardiac Troponin ◽

Muscle Fibers ◽

Troponin C ◽

Partial Substitution ◽

Tension Development ◽

Cardiac Troponin C ◽

Skeletal Muscle Fibers

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Structural Kinetics of Cardiac Troponin C Mutants Linked to Familial Hypertrophic and Dilated Cardiomyopathy in Troponin Complexes

Journal of Biological Chemistry ◽

10.1074/jbc.m703822200 ◽

2007 ◽

Vol 283 (6) ◽

pp. 3424-3432 ◽

Cited By ~ 41

Author(s):

Wen-Ji Dong ◽

Jun Xing ◽

Yexin Ouyang ◽

Jianli An ◽

Herbert C. Cheung

Keyword(s):

Dilated Cardiomyopathy ◽

Cardiac Troponin ◽

Troponin C ◽

Cardiac Troponin C ◽

Kinetics Of

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Increasing mammalian cardiomyocyte contractility with residues identified in trout troponin C

Physiological Genomics ◽

10.1152/physiolgenomics.00007.2005 ◽

2005 ◽

Vol 22 (1) ◽

pp. 1-7 ◽

Cited By ~ 22

Author(s):

Todd E. Gillis ◽

Bo Liang ◽

Franca Chung ◽

Glen F. Tibbits

Keyword(s):

Amino Acid ◽

Cardiac Myocytes ◽

Cardiac Troponin ◽

Troponin C ◽

Force Generation ◽

Wild Type ◽

Cardiac Troponin C ◽

Cardiomyocyte Contractility

The Ca2+ sensitivity of force generation in trout cardiac myocytes is significantly greater than that from mammalian hearts. One mechanism that we have suggested to be responsible, at least in part, for this high Ca2+ sensitivity is the isoform of cardiac troponin C (cTnC) found in trout hearts (ScTnC), which has greater than twice the Ca2+ affinity of mammalian cTnC (McTnC). Here, through a series of mutations, the residues in ScTnC responsible for its high Ca2+ affinity have been identified as being Asn2, Ile28, Gln29, and Asp30. When these residues in McTnC were mutated to the trout-equivalent amino acid, the Ca2+ affinity of the molecule, determined by monitoring the fluorescence of a Trp inserted for a Phe at residue 27, is comparable to that of ScTnC. To determine how a McTnC mutant containing Asn2, Ile28, Gln29, and Asp30 (NIQD McTnC) affects the Ca2+ sensitivity of force generation, endogenous cTnC in single, chemically skinned rabbit cardiomyocytes was replaced with either wild-type McTnC or NIQD McTnC. Our results demonstrate that the cardiomyocytes containing NIQD McTnC were approximately twice as sensitive to Ca2+, illustrating that a McTnC mutant with similar Ca2+ affinity as ScTnC can be used to sensitize mammalian cardiac myocytes to Ca2+.

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