Effects of a Cardiomyopathy-causing Troponin T Mutation on Thin Filament Function and Structure

Burhop, James; Rosol, Michael; Craig, Roger; Tobacman, Larry S.; Lehman, William

doi:10.1074/jbc.m101110200

Cited by 24 publications

(30 citation statements)

References 53 publications

(74 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In contrast to the weakened coupling of cTnT-⌬E8 to TnI, the results may reflect a strengthened coupling between cTnT-⌬E8 and Tm, which may also affect the allosteric feature of the thin filament regulatory system. This hypothesis is in agreement with the observation that a COOH-terminal truncation of cTnT found in human familial hypertrophic cardiomyopathy was shown to alter the activation of thin filament through destabilization of the thin filament inhibition state, which is responsible for the pathological phenotypes (51).…”

Section: Exon 8 Deletion Altered the Binding Affinity Of Ctnt To Tni supporting

confidence: 79%

Exon Skipping in Cardiac Troponin T of Turkeys with Inherited Dilated Cardiomyopathy

Biesiadecki¹,

Jin

2002

Journal of Biological Chemistry

View full text Add to dashboard Cite

Troponin T is a central component of the thin filament-associated troponin-tropomyosin system and plays an essential role in the Ca 2؉ regulation of striated muscle contraction. The importance of the structure and function of troponin T is evident in the regulated isoform expression during development and the point mutations resulting in familial hypertrophic and dilated cardiomyopathies. We report here that turkeys with inherited dilated cardiomyopathy and heart failure express an unusual low molecular weight cardiac troponin T missing 11 amino acids due to the splice out of the normally conserved exon 8-encoded segment. The deletion of a 9-bp segment from intron 7 of the turkey cardiac troponin T gene may be responsible for the weakened splicing of the downstream exon 8 during mRNA processing. The exclusion of the exon 8-encoded segment results in conformational changes in cardiac troponin T, an altered binding affinity for troponin I and tropomyosin, and an increased calcium sensitivity of the actomyosin ATPase. Expression of the exon 8-deleted cardiac troponin T prior to the development of cardiomyopathy in turkeys indicates a novel RNA splicing disease and provides evidence for the role of troponin T structure-function variation in myocardial pathogenesis and heart failure.

show abstract

Section: Exon 8 Deletion Altered the Binding Affinity Of Ctnt To Tni supporting

confidence: 79%

Exon Skipping in Cardiac Troponin T of Turkeys with Inherited Dilated Cardiomyopathy

Biesiadecki¹,

Jin

2002

Journal of Biological Chemistry

View full text Add to dashboard Cite

show abstract

“…4B). This is in good agreement with solution studies with reconstituted HCM mutant troponin-tropomyosin proteins [in cTnI (19) and cTnT (18)] that support for a disrupted B state. The C-terminal half of cTnI (residues 137-210) docks the troponin-tropomyosin complex onto the outer domain of actin at low [Ca 2+ ] and thereby maintains formation of the B state (34).…”

Section: Discussionsupporting

confidence: 76%

“…In addition, it could represent a pathomechanism underlying the diastolic dysfunction seen in both disease states. Solution studies with mutant troponin proteins, which are known to cause HCM, showed a reduction in the B state at low-Ca 2+ conditions compared with wild-type troponin proteins (18,19). Mutation-induced irregularities in troponin-tropomyosin interactions disrupt the B state and shift the thin filament to the C state, increasing the available myosin-binding sites on actin.…”

mentioning

confidence: 99%

ADP-stimulated contraction: A predictor of thin-filament activation in cardiac disease

Sequeira

Najafi

Wijnker

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

Diastolic dysfunction is general to all idiopathic dilated (IDCM) and hypertrophic cardiomyopathy (HCM) patients. Relaxation deficits may result from increased actin-myosin formation during diastole due to altered tropomyosin position, which blocks myosin binding to actin in the absence of Ca 2+ . We investigated whether ADP-stimulated force development (without Ca 2+ ) can be used to reveal changes in actin-myosin blockade in human cardiomyopathy cardiomyocytes. Cardiac samples from HCM patients, harboring thick-filament (MYH7 mut , MYBPC3 mut ) and thin-filament (TNNT2 mut , TNNI3 mut ) mutations, and IDCM were compared with sarcomere mutation-negative HCM (HCM smn ) and nonfailing donors. Myofilament ADP sensitivity was higher in IDCM and HCM compared with donors, whereas it was lower for MYBPC3. Increased ADP sensitivity in IDCM, HCM smn , and MYH7 mut was caused by low phosphorylation of myofilament proteins, as it was normalized to donors by protein kinase A (PKA) treatment. Troponin exchange experiments in a TNNT2 mut sample corrected the abnormal actin-myosin blockade. In MYBPC3 trunc samples, ADP sensitivity highly correlated with cardiac myosin-binding protein-C (cMyBP-C) protein level. Incubation of cardiomyocytes with cMyBP-C antibody against the actin-binding N-terminal region reduced ADP sensitivity, indicative of cMyBP-C's role in actin-myosin regulation. In the presence of Ca 2+ , ADP increased myofilament force development and sarcomere stiffness. Enhanced sarcomere stiffness in sarcomere mutation-positive HCM samples was irrespective of the phosphorylation background. In conclusion, ADP-stimulated contraction can be used as a tool to study how protein phosphorylation and mutant proteins alter accessibility of myosin binding on actin. In the presence of Ca 2+ , pathologic [ADP] and low PKA-phosphorylation, high actin-myosin formation could contribute to the impaired myocardial relaxation observed in cardiomyopathies.H eart failure (HF) is a syndrome clinically defined as the inability of the heart to sufficiently supply blood to organs and tissues (1). Systolic dysfunction is present in approximately one-half of the HF population, whereas diastolic dysfunction is a common feature in almost all HF patients (2). Moreover, in hypertrophic cardiomyopathy (HCM), which is caused by mutations in genes encoding thinand thick-filament proteins, impaired diastolic function is frequently observed (3). Impaired relaxation of the heart may be caused by high myofilament Ca 2+ sensitivity. This increased sensitivity for Ca 2+ would result in residual myofilament activation at diastolic [Ca 2+ ], which may delay the onset of ventricular relaxation and limit proper filling of the heart. High myofilament Ca 2+ sensitivity has been observed in both acquired and genetic forms of cardiomyopathy (3, 4). In human idiopathic dilated cardiomyopathy (IDCM), high myofilament Ca 2+ sensitivity has been associated with reduced β-adrenergic receptor-mediated phosphorylation by protein kinase A (PKA) (4). Reduced PKA phospho...

show abstract

“…In the absence of myosin, tropomyosin is shown schematically at the junction between the actin inner and outer domains (termed the C-state (6)). Tropomyosin in the C-state interferes sterically with strong myosin binding to actin, as supported by both structural (7,8) and functional (25,38,45) data. Cooperative shifting of tropomyosin away from the C-state position, i.e.…”

Section: Figmentioning

confidence: 80%

Modulation of Myosin Function by Isoform-specific Properties ofSaccharomyces cerevisiae and Muscle Tropomyosins

Strand¹,

Nili²,

Homsher³

et al. 2001

Journal of Biological Chemistry

Self Cite

View full text Add to dashboard Cite

Tropomyosin is an extended coiled-coil protein that influences actin function by binding longitudinally along thin filaments. The present work compares cardiac tropomyosin and the two tropomyosins from Saccharomyces cerevisiae, TPM1 and TPM2, that are much shorter than vertebrate tropomyosins. Unlike cardiac tropomyosin, the phase of the coiled-coil-forming heptad repeat of TPM2 is discontinuous; it is interrupted by a 4-residue deletion. TPM1 has two such deletions, which flank the 38-residue partial gene duplication that causes TPM1 to span five actins instead of the four of TPM2. Each of the three tropomyosin isoforms modulates actin-myosin interactions, with isoform-specific effects on cooperativity and strength of myosin binding. These different properties can be explained by a model that combines opposite effects, steric hindrance between myosin and tropomyosin when the latter is bound to a subset of its sites on actin, and also indirect, favorable interactions between tropomyosin and myosin, mediated by mutually promoted changes in actin. Both of these effects are influenced by which tropomyosin isoform is present. Finally, the tropomyosins have isoformspecific effects on in vitro sliding speed and on the myosin concentration dependence of this movement, suggesting that non-muscle tropomyosin isoforms exist, at least in part, to modulate myosin function.Tropomyosin is a highly elongated coiled-coil protein that binds to actin filaments in both muscle and non-muscle cells. Tropomyosin, which has many isoforms, stabilizes actin filaments against fragmentation, and by its presence on the thin filament has the potential to influence many aspects of F-actin function. In particular, tropomyosins have complex and incompletely understood effects on actin-myosin interactions. One consistent finding is that vertebrate tropomyosins increase the affinity of myosin subfragment-1 for actin (1-5), despite steric hindrance between the preferred binding sites for tropomyosin and myosin S1 1 when they bind to actin separately (6 -8). Saccharomyces cerevisiae has two tropomyosin isoforms, TPM1 and TPM2, both of them substantially shorter than vertebrate tropomyosins (9, 10). The 199-residue TPM1 is the predominant isoform by expression level, and it spans five actin monomers. TPM2 is 161 residues and spans four actin monomers, whereas vertebrate tropomyosins span either six or seven actin monomers. Like other tropomyosins, TPM1 and TPM2 have the classical heptad repeat that is responsible for coiled-coil formation, in which hydrophobic residues are found in the first and fourth positions of successive groups of seven amino acids. Below we show that, unlike other tropomyosins, this motif is interrupted once (TPM2) or twice (TPM1) in the amino acid sequence; the phase of the heptad pattern shifts, due to four residue deletions. Both the short length and the interrupted heptad pattern of yeast tropomyosins suggest they could significantly differ from vertebrate tropomyosins functionally. In the present report we describe the s...

show abstract

Effects of a Cardiomyopathy-causing Troponin T Mutation on Thin Filament Function and Structure

Cited by 24 publications

References 53 publications

Exon Skipping in Cardiac Troponin T of Turkeys with Inherited Dilated Cardiomyopathy

Exon Skipping in Cardiac Troponin T of Turkeys with Inherited Dilated Cardiomyopathy

ADP-stimulated contraction: A predictor of thin-filament activation in cardiac disease

Modulation of Myosin Function by Isoform-specific Properties ofSaccharomyces cerevisiae and Muscle Tropomyosins

Contact Info

Product

Resources

About