Single Particle Analysis of Relaxed and Activated Muscle Thin Filaments

Pirani, Alnoor; Xu, Chen; Hatch, Victoria; Craig, Roger; Tobacman, Larry S.; Lehman, William

doi:10.1016/j.jmb.2004.12.013

Cited by 110 publications

(187 citation statements)

References 56 publications

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“…Native thin filaments, or F-actin preincubated with tropomyosin and troponin (60), were mixed with varying ratios of C0C1f and C0C2 under different buffer conditions used in previous thin filament studies (27,36,37,60). Five-microliter aliquots were applied to EM grids coated with thin carbon and negatively stained with 1% (wt/vol) uranyl acetate.…”

Section: Methodsmentioning

confidence: 99%

Myosin-binding protein C displaces tropomyosin to activate cardiac thin filaments and governs their speed by an independent mechanism

Mun

Previs

et al. 2014

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

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148

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Significance Myosin-binding protein C (MyBP-C) is a component of myosin filaments, one of the two sets of contractile elements whose relative sliding is the basis of muscle contraction. In the heart, MyBP-C modulates contractility in response to cardiac stimulation; mutations in MyBP-C lead to cardiac disease. The mechanism by which MyBP-C modulates cardiac contraction is not understood. Using electron microscopy and a light microscopic assay for filament sliding, we demonstrate that MyBP-C binds to the other set of filaments, containing actin and the regulatory component, tropomyosin. In so doing, it displaces tropomyosin from its inhibitory position to activate actin filament interaction with myosin, promoting filament sliding. These findings provide insights into the molecular basis of heart function.

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Section: Methodsmentioning

confidence: 99%

Myosin-binding protein C displaces tropomyosin to activate cardiac thin filaments and governs their speed by an independent mechanism

Mun

Previs

et al. 2014

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

Self Cite

148

207

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“…The steric blocking model of muscle regulation holds that at relaxing (low Ca 2+ ) conditions Tpm blocks myosin binding sites on the surface of F-actin, whereas Tpm moves away from the myosin binding sites at activating (high Ca 2+ ) conditions (2,3). Kinetics, biochemical, and structural studies have suggested that there are three structural states for Tpm, termed "blocked," "closed," and "myosin" ("open"), which correspond to relaxing, activating, and myosin-bound conditions, respectively (4)(5)(6). The current model of the muscle regulation is based on the analysis of negatively stained TFs and suggests a two-step muscle activation (3,7).…”

mentioning

confidence: 99%

“…All our current structural knowledge on the Ca 2+ activation of the TF relies on the analysis of negatively stained TFs (3,5,14). Recent studies on the interaction of F-actin with Tpm demonstrated that the position of Tpm on the surface of F-actin is different in negatively stained and frozen hydrated samples (15).…”

mentioning

confidence: 99%

Ca ²⁺ -induced movement of tropomyosin on native cardiac thin filaments revealed by cryoelectron microscopy

Risi

Eisner

Belknap

et al. 2017

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

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Muscle contraction relies on the interaction of myosin motors with F-actin, which is regulated through a translocation of tropomyosin by the troponin complex in response to Ca 2+ . The current model of muscle regulation holds that at relaxing (low-Ca 2+ ) conditions tropomyosin blocks myosin binding sites on F-actin, whereas at activating (high-Ca 2+ ) conditions tropomyosin translocation only partially exposes myosin binding sites on F-actin so that binding of rigor myosin is required to fully activate the thin filament (TF). Here we used a single-particle approach to helical reconstruction of frozen hydrated native cardiac TFs under relaxing and activating conditions to reveal the azimuthal movement of the tropomyosin on the surface of the native cardiac TF upon Ca 2+ activation. We demonstrate that at either relaxing or activating conditions tropomyosin is not constrained in one structural state, but rather is distributed between three structural positions on the surface of the TF. We show that two of these tropomyosin positions restrain actomyosin interactions, whereas in the third position, which is significantly enhanced at high Ca 2+ , tropomyosin does not block myosin binding sites on F-actin. Our data provide a structural framework for the enhanced activation of the cardiac TF over the skeletal TF by Ca 2+ and lead to a mechanistic model for the regulation of the cardiac TF.thin filament | cardiac muscle regulation | cryoelectron microscopy

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“…The approximate position of the inhibitory region of TnI is indicated in the top panel by the white arrow. The structure and relative positions employed to construct these projections are based on data obtained for rabbit skeletal muscle (actin) and bovine cardiac muscle (troponin and tropomyosin) by the Lehman group using electron microscopy data and helical and single particle reconstruction [55,56] …”

Section: Future Perspectivesmentioning

confidence: 99%

Cardiac thin filament regulation

Kobayashi

Liu

Tombe

2008

Pflugers Arch - Eur J Physiol

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Myocardial contraction is initiated upon the release of calcium into the cytosol from the sarcoplasmic reticulum following membrane depolarization. The fundamental physiological role of the heart is to pump an amount blood that is determined by the prevailing requirements of the body. The physiological control systems employed to accomplish this task include regulation of heart rate, the amount of calcium release, and the response of the cardiac myofilaments to activator calcium ions. Thin filament activation and relaxation dynamics has emerged as a pivotal regulatory system tuning myofilament function to the beat-to-beat regulation of cardiac output. Maladaptation of thin filament dynamics, in addition to dysfunctional calcium cycling, is now recognized as an important cellular mechanism causing reduced cardiac pump function in a variety of cardiac diseases. Here, we review current knowledge regarding protein-protein interactions involved in the dynamics of thin filament activation and relaxation and the regulation of these processes by protein kinase-mediated phosphorylation.

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Single Particle Analysis of Relaxed and Activated Muscle Thin Filaments

Cited by 110 publications

References 56 publications

Myosin-binding protein C displaces tropomyosin to activate cardiac thin filaments and governs their speed by an independent mechanism

Myosin-binding protein C displaces tropomyosin to activate cardiac thin filaments and governs their speed by an independent mechanism

Ca ²⁺ -induced movement of tropomyosin on native cardiac thin filaments revealed by cryoelectron microscopy

Cardiac thin filament regulation

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Single Particle Analysis of Relaxed and Activated Muscle Thin Filaments

Cited by 110 publications

References 56 publications

Myosin-binding protein C displaces tropomyosin to activate cardiac thin filaments and governs their speed by an independent mechanism

Myosin-binding protein C displaces tropomyosin to activate cardiac thin filaments and governs their speed by an independent mechanism

Ca 2+ -induced movement of tropomyosin on native cardiac thin filaments revealed by cryoelectron microscopy

Cardiac thin filament regulation

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Ca ²⁺ -induced movement of tropomyosin on native cardiac thin filaments revealed by cryoelectron microscopy