scholarly journals Structure of the thin filament in native skeletal muscles reveals its interaction with nebulin and two distinct conformations of myosin

2021 ◽  
Author(s):  
Zhexin Wang ◽  
Michael Grange ◽  
Sabrina Pospich ◽  
Thorsten Wagner ◽  
Ay Lin Kho ◽  
...  
Keyword(s):  
Thin Filament ◽  
Troponin T ◽  
Atomic Scale ◽  
Structural Protein ◽  
Thin Filaments ◽  
Binding Motifs ◽  
Structural Mechanism ◽  
Molecular Ruler ◽  
Electron Cryotomography ◽  
The Impact

AbstractNebulin is a major structural protein of skeletal sarcomeres and is essential for proper assembly and contraction of skeletal muscle1. It stabilises and regulates the length of thin filaments,2 but the structural mechanism remains nebulous. Using electron cryotomography and sub-tomogram averaging, we present the first structure of native nebulin bound to thin filaments within the A-band and I-band of intact sarcomeres. This in-situ reconstruction reveals unprecedented detail of interaction at pseudo-atomic resolution between nebulin and actin, providing the basis for understanding the structural and regulatory roles of nebulin. The position of nebulin on the thin filament indicates that there is no contact to tropomyosin or myosin, but an unexpected interaction with a troponin-T linker, possibly through two binding motifs on nebulin. In addition, our structure of myosin bound to the thin filaments reveals different conformations of the neck domain, both within the same sarcomere and when compared to purified structures, highlighting an inherent structural variability in muscle. We provide a complete description of cross-bridge formation on fully native, nebulin-containing thin filaments at near-atomic scale. Our structures establish the molecular basis for the role of nebulin as a thin filament “molecular ruler” and the impact of nemaline myopathies mutations that will aid future development of therapies.

scholarly journals Ca2+-dependent Muscle Dysfunction Caused by Mutation of the Caenorhabditis elegans Troponin T-1 Gene

1998 ◽  
Vol 143 (5) ◽  
pp. 1201-1213 ◽  
Author(s):  
Kristen McArdle ◽  
Taylor StC. Allen ◽  
Elizabeth A. Bucher
Keyword(s):  
Caenorhabditis Elegans ◽  
Thin Filament ◽  
Body Wall ◽  
Troponin I ◽  
Troponin T ◽  
Muscle Dysfunction ◽  
Excessive Force ◽  
Thin Filaments ◽  
Attachment Sites

We have investigated the functions of troponin T (CeTnT-1) in Caenorhabditis elegans embryonic body wall muscle. TnT tethers troponin I (TnI) and troponin C (TnC) to the thin filament via tropomyosin (Tm), and TnT/Tm regulates the activation and inhibition of myosin-actin interaction in response to changes in intracellular [Ca2+]. Loss of CeTnT-1 function causes aberrant muscle trembling and tearing of muscle cells from their exoskeletal attachment sites (Myers, C.D., P.-Y. Goh, T. StC. Allen, E.A. Bucher, and T. Bogaert. 1996. J. Cell Biol. 132:1061–1077). We hypothesized that muscle tearing is a consequence of excessive force generation resulting from defective tethering of Tn complex proteins. Biochemical studies suggest that such defective tethering would result in either (a) Ca2+-independent activation, due to lack of Tn complex binding and consequent lack of inhibition, or (b) delayed reestablishment of TnI/TnC binding to the thin filament after Ca2+ activation and consequent abnormal duration of force. Analyses of animals doubly mutant for CeTnT-1 and for genes required for Ca2+ signaling support that CeTnT-1 phenotypes are dependent on Ca2+ signaling, thus supporting the second model and providing new in vivo evidence that full inhibition of thin filaments in low [Ca2+] does not require TnT.

scholarly journals Nebulin regulates actin filament lengths by a stabilization mechanism

2010 ◽  
Vol 189 (5) ◽  
pp. 859-870 ◽  
Author(s):  
Christopher T. Pappas ◽  
Paul A. Krieg ◽  
Carol C. Gregorio
Keyword(s):  
Muscle Contraction ◽  
Actin Filament ◽  
Thin Filament ◽  
Stabilization Mechanism ◽  
Thin Filaments ◽  
Skeletal Myocytes ◽  
Actin Depolymerization ◽  
Molecular Ruler ◽  
Dynamic Populations ◽  
Highly Cited

Efficient muscle contraction requires regulation of actin filament lengths. In one highly cited model, the giant protein nebulin has been proposed to function as a molecular ruler specifying filament lengths. We directly challenged this hypothesis by constructing a unique, small version of nebulin (mini-nebulin). When endogenous nebulin was replaced with mini-nebulin in skeletal myocytes, thin filaments extended beyond the end of mini-nebulin, an observation which is inconsistent with a strict ruler function. However, under conditions that promote actin filament depolymerization, filaments associated with mini-nebulin were remarkably maintained at lengths either matching or longer than mini-nebulin. This indicates that mini-nebulin is able to stabilize portions of the filament it has no contact with. Knockdown of nebulin also resulted in more dynamic populations of thin filament components, whereas expression of mini-nebulin decreased the dynamics at both filament ends (i.e., recovered loss of endogenous nebulin). Thus, nebulin regulates thin filament architecture by a mechanism that includes stabilizing the filaments and preventing actin depolymerization.

scholarly journals Overexpression of troponin T in Drosophila muscles causes a decrease in the levels of thin-filament proteins

2005 ◽  
Vol 386 (1) ◽  
pp. 145-152 ◽  
Author(s):  
Raquel MARCO-FERRERES ◽  
Juan J. ARREDONDO ◽  
Benito FRAILE ◽  
Margarita CERVERA
Keyword(s):  
Thin Filament ◽  
Troponin I ◽  
Troponin T ◽  
Thin Filaments ◽  
Muscle Formation ◽  
Thin Filament Proteins ◽  
Flight Muscles ◽  
Transgenic Drosophila ◽  
Regulated Thin Filament

Formation of the contractile apparatus in muscle cells requires co-ordinated activation of several genes and the proper assembly of their products. To investigate the role of TnT (troponin T) in the mechanisms that control and co-ordinate thin-filament formation, we generated transgenic Drosophila lines that overexpress TnT in their indirect flight muscles. All flies that overexpress TnT were unable to fly, and the loss of thin filaments themselves was coupled with ultrastructural perturbations of the sarcomere. In contrast, thick filaments remained largely unaffected. Biochemical analysis of these lines revealed that the increase in TnT levels could be detected only during the early stages of adult muscle formation and was followed by a profound decrease in the amount of this protein as well as that of other thin-filament proteins such as tropomyosin, troponin I and actin. The decrease in thin-filament proteins is not only due to degradation but also due to a decrease in their synthesis, since accumulation of their mRNA transcripts was also severely diminished. This decrease in expression levels of the distinct thin-filament components led us to postulate that any change in the amount of TnT transcripts might trigger the down-regulation of other co-regulated thin-filament components. Taken together, these results suggest the existence of a mechanism that tightly co-ordinates the expression of thin-filament genes and controls the correct stoichiometry of these proteins. We propose that the high levels of unassembled protein might act as a sensor in this process.

scholarly journals Divergent effects of α- and β-myosin heavy chain isoforms on the N terminus of rat cardiac troponin T

2013 ◽  
Vol 142 (4) ◽  
pp. 413-423 ◽  
Author(s):  
Ranganath Mamidi ◽  
Murali Chandra
Keyword(s):  
Myosin Heavy Chain ◽  
Heavy Chain ◽  
Cardiac Troponin ◽  
Thin Filament ◽  
Troponin T ◽  
Myosin Heavy Chain Isoforms ◽  
Cardiac Troponin T ◽  
N Terminus ◽  
Cross Bridges ◽  
The Impact

Divergent effects of α– and β–myosin heavy chain (MHC) isoforms on contractile behavior arise mainly because of their impact on thin filament cooperativity. The N terminus of cardiac troponin T (cTnT) also modulates thin filament cooperativity. Our hypothesis is that the impact of the N terminus of cTnT on thin filament activation is modulated by a shift from α- to β-MHC isoform. We engineered two recombinant proteins by deleting residues 1–43 and 44–73 in rat cTnT (RcTnT): RcTnT1–43Δ and RcTnT44–73Δ, respectively. Dynamic and steady-state contractile parameters were measured at sarcomere length of 2.3 µm after reconstituting proteins into detergent-skinned muscle fibers from normal (α-MHC) and propylthiouracil-treated (β-MHC) rat hearts. α-MHC attenuated Ca2+-activated maximal tension (∼46%) in RcTnT1–43Δ fibers. In contrast, β-MHC decreased tension only by 19% in RcTnT1–43Δ fibers. Both α- and β-MHC did not affect tension in RcTnT44–73Δ fibers. The instantaneous muscle fiber stiffness measurements corroborated the divergent impact of α- and β-MHC on tension in RcTnT1–43Δ fibers. pCa50 (-log of [Ca2+]free required for half-maximal activation) decreased significantly by 0.13 pCa units in α-MHC + RcTnT1–43Δ fibers but remained unaltered in β-MHC + RcTnT1–43Δ fibers, demonstrating that β-MHC counteracted the attenuating effect of RcTnT1–43Δ on myofilament Ca2+ sensitivity. β-MHC did not alter the sudden stretch–mediated recruitment of new cross-bridges (ER) in RcTnT1–43Δ fibers, but α-MHC attenuated ER by 36% in RcTnT1–43Δ fibers. The divergent impact of α- and β-MHC on how the N terminus of cTnT modulates contractile dynamics has implications for heart disease; alterations in cTnT and MHC are known to occur via changes in isoform expression or mutations.

scholarly journals The functional effect of dilated cardiomyopathy mutation (R144W) in mouse cardiac troponin T is differently affected by α- and β-myosin heavy chain isoforms

2015 ◽  
Vol 308 (8) ◽  
pp. H884-H893 ◽  
Author(s):  
Sampath K. Gollapudi ◽  
Jil C. Tardiff ◽  
Murali Chandra
Keyword(s):  
Dilated Cardiomyopathy ◽  
Myosin Heavy Chain ◽  
Transgenic Mouse ◽  
Heavy Chain ◽  
Thin Filament ◽  
Troponin T ◽  
Myosin Heavy Chain Isoforms ◽  
Cardiac Muscle Fibers ◽  
The Impact ◽  
Functional Phenotype

Given the differential impact of α- and β-myosin heavy chain (MHC) isoforms on how troponin T (TnT) modulates contractile dynamics, we hypothesized that the effects of dilated cardiomyopathy (DCM) mutations in TnT would be altered differently by α- and β-MHC. We characterized dynamic contractile features of normal (α-MHC) and transgenic (β-MHC) mouse cardiac muscle fibers reconstituted with a mouse TnT analog (TnTR144W) of the human DCM R141W mutation. TnTR144W did not alter maximal tension but attenuated myofilament Ca2+ sensitivity ( pCa50) to a similar extent in α- and β-MHC fibers. TnTR144W attenuated the speed of cross-bridge (XB) distortion dynamics ( c) by 24% and the speed of XB recruitment dynamics ( b) by 17% in α-MHC fibers; however, both b and c remained unaltered in β-MHC fibers. Likewise, TnTR144W attenuated the rates of XB detachment ( g) and tension redevelopment ( ktr) only in α-MHC fibers. TnTR144W also decreased the impact of strained XBs on the recruitment of new XBs (γ) by 30% only in α-MHC fibers. Because c, b, g, ktr, and γ are strongly influenced by thin filament-based cooperative mechanisms, we conclude that the TnTR144W- and β-MHC-mediated changes in the thin filament interact to produce a less severe functional phenotype, compared with that brought about by TnTR144W and α-MHC. These observations provide a basis for lower mortality rates of humans (β-MHC) harboring the TnTR141W mutant compared with transgenic mouse studies. Our findings strongly suggest that some caution is necessary when extrapolating data from transgenic mouse studies to human hearts.

Atomic resolution characterisation of interface structures by Electron Energy Loss Spectroscopy

1993 ◽  
Vol 51 ◽  
pp. 576-577
Author(s):  
N. D. Browning ◽  
M. M. McGibbon ◽  
M. F. Chisholm ◽  
S. J. Pennycook
Keyword(s):  
High Resolution ◽  
Energy Loss ◽  
Electron Energy ◽  
Electron Energy Loss Spectroscopy ◽  
Imaging Technique ◽  
Atomic Scale ◽  
Atomic Resolution ◽  
Reference Image ◽  
The Impact ◽  
Electron Energy Loss

The recent development of the Z-contrast imaging technique for the VG HB501 UX dedicated STEM, has added a high-resolution imaging facility to a microscope used mainly for microanalysis. This imaging technique not only provides a high-resolution reference image, but as it can be performed simultaneously with electron energy loss spectroscopy (EELS), can be used to position the electron probe at the atomic scale. The spatial resolution of both the image and the energy loss spectrum can be identical, and in principle limited only by the 2.2 Å probe size of the microscope. There now exists, therefore, the possibility to perform chemical analysis of materials on the scale of single atomic columns or planes.In order to achieve atomic resolution energy loss spectroscopy, the range over which a fast electron can cause a particular excitation event, must be less than the interatomic spacing. This range is described classically by the impact parameter, b, which ranges from ~10 Å for the low loss region of the spectrum to <1Å for the core losses.

scholarly journals Prognostic implications of troponin T variations in inherited cardiomyopathies using systems biology

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Rameen Shakur ◽  
Juan Pablo Ochoa ◽  
Alan J. Robinson ◽  
Abhishek Niroula ◽  
Aneesh Chandran ◽  
...  
Keyword(s):  
Heart Failure ◽  
Systems Biology ◽  
Sudden Cardiac Death ◽  
Risk Stratification ◽  
Clinical Data ◽  
Cardiac Death ◽  
Troponin T ◽  
Management Options ◽  
Familial Cardiomyopathy ◽  
The Impact

AbstractThe cardiac troponin T variations have often been used as an example of the application of clinical genotyping for prognostication and risk stratification measures for the management of patients with a family history of sudden cardiac death or familial cardiomyopathy. Given the disparity in patient outcomes and therapy options, we investigated the impact of variations on the intermolecular interactions across the thin filament complex as an example of an unbiased systems biology method to better define clinical prognosis to aid future management options. We present a novel unbiased dynamic model to define and analyse the functional, structural and physico-chemical consequences of genetic variations among the troponins. This was subsequently integrated with clinical data from accessible global multi-centre systematic reviews of familial cardiomyopathy cases from 106 articles of the literature: 136 disease-causing variations pertaining to 981 global clinical cases. Troponin T variations showed distinct pathogenic hotspots for dilated and hypertrophic cardiomyopathies; considering the causes of cardiovascular death separately, there was a worse survival in terms of sudden cardiac death for patients with a variation at regions 90–129 and 130–179 when compared to amino acids 1–89 and 200–288. Our data support variations among 90–130 as being a hotspot for sudden cardiac death and the region 131–179 for heart failure death/transplantation outcomes wherein the most common phenotype was dilated cardiomyopathy. Survival analysis into regions of high risk (regions 90–129 and 130–180) and low risk (regions 1–89 and 200–288) was significant for sudden cardiac death (p = 0.011) and for heart failure death/transplant (p = 0.028). Our integrative genomic, structural, model from genotype to clinical data integration has implications for enhancing clinical genomics methodologies to improve risk stratification.

scholarly journals Site-specific N-glycosylation analysis of animal cell culture-derived Zika virus proteins

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Alexander Pralow ◽  
Alexander Nikolay ◽  
Arnaud Leon ◽  
Yvonne Genzel ◽  
Erdmann Rapp ◽  
...  
Keyword(s):  
Zika Virus ◽  
Animal Cell ◽  
Gradient Centrifugation ◽  
Viral Envelope ◽  
Protein Glycosylation ◽  
High Yield ◽  
Structural Protein ◽  
Site Specific ◽  
E Protein ◽  
The Impact

AbstractHere, we present for the first time, a site-specific N-glycosylation analysis of proteins from a Brazilian Zika virus (ZIKV) strain. The virus was propagated with high yield in an embryo-derived stem cell line (EB66, Valneva SE), and concentrated by g-force step-gradient centrifugation. Subsequently, the sample was proteolytically digested with different enzymes, measured via a LC–MS/MS-based workflow, and analyzed in a semi-automated way using the in-house developed glyXtoolMS software. The viral non-structural protein 1 (NS1) was glycosylated exclusively with high-mannose structures on both potential N-glycosylation sites. In case of the viral envelope (E) protein, no specific N-glycans could be identified with this method. Nevertheless, N-glycosylation could be proved by enzymatic de-N-glycosylation with PNGase F, resulting in a strong MS-signal of the former glycopeptide with deamidated asparagine at the potential N-glycosylation site N444. This confirmed that this site of the ZIKV E protein is highly N-glycosylated but with very high micro-heterogeneity. Our study clearly demonstrates the progress made towards site-specific N-glycosylation analysis of viral proteins, i.e. for Brazilian ZIKV. It allows to better characterize viral isolates, and to monitor glycosylation of major antigens. The method established can be applied for detailed studies regarding the impact of protein glycosylation on antigenicity and human pathogenicity of many viruses including influenza virus, HIV and corona virus.

scholarly journals Effects of peak time of myocardial injury biomarkers on mid-term outcomes of patients undergoing OPCABG

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Bo Hu ◽  
Fei Gao ◽  
Mengwei Lv ◽  
Ban Liu ◽  
Yu Shi ◽  
...  
Keyword(s):  
Myocardial Injury ◽  
Cox Regression ◽  
Troponin T ◽  
Artery Bypass ◽  
Left Ventricular ◽  
Left Ventricular Ejection ◽  
Peak Time ◽  
Clinical Trial Registry ◽  
Ventricular Ejection Fraction ◽  
The Impact

Abstract Background With the development of cardiac surgery techniques, myocardial injury is gradually reduced, but cannot be completely avoided. Myocardial injury biomarkers (MIBs) can quickly and specifically reflect the degree of myocardial injury. Due to various reasons, there is no consensus on the specific values of MIBs in evaluating postoperative prognosis. This retrospective study was aimed to investigate the impact of MIBs on the mid-term prognosis of patients undergoing off-pump coronary artery bypass grafting (OPCABG). Methods Totally 564 patients undergoing OPCABG with normal courses were included. Cardiac troponin T (cTnT) and creatine kinase myocardial band (CK-MB) were assessed within 48 h before operation and at 6, 12, 24, 48, 72, 96 and 120 h after operation. Patients were grouped by peak values and peak time courses of MIBs. The profile of MIBs and clinical variables as well as their correlations with mid-term prognosis were analyzed by univariable and multivariable Cox regression models. Result Continuous assessment showed that MIBs increased first (12 h after surgery) and then decreased. The peak cTnT and peak CK-MB occurred within 24 h after operation in 76.8% and 67.7% of the patients respectively. No significant correlation was found between CK-MB and mid-term mortality. Delayed cTnT peak (peak cTnT elevated after 24 h after operation) was correlated with lower creatinine clearance rate (69.36 ± 21.67 vs. 82.18 ± 25.17 ml/min/1.73 m2), body mass index (24.35 ± 2.58 vs. 25.27 ± 3.26 kg/m2), less arterial grafts (1.24 ± 0.77 vs. 1.45 ± 0.86), higher EuroSCORE II (2.22 ± 1.12 vs.1.72 ± 0.91) and mid-term mortality (26.5 vs.7.9%). Age (HR: 1.067, CI: 1.006–1.133), left ventricular ejection fraction (HR: 0.950, CI: 0.910–0.993), New York Heart Association score (HR: 1.839, CI: 1.159–2.917), total venous grafting (HR: 2.833, CI: 1.054–7.614) and cTnT peak occurrence within 24 h (HR: 0.362, CI: 0.196–0.668) were independent predictors of mid-term mortality. Conclusion cTnT is a better indicator than CK-MB. The peak value and peak occurrence of cTnT are related to mid-term mortality in patients undergoing OPCABG, and the peak phases have stronger predictive ability. Trial registration: Chinese Clinical Trial Registry, ChiCTR2000033850. Registered 14 June 2020, http://www.chictr.org.cn/edit.aspx?pid=55162&htm=4.

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