Three-dimensional structure of vertebrate cardiac muscle filaments

Department of Cell Biology, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, MA 01655, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 03/2008; 105(7):2386-90. DOI: 10.1073/pnas.0708912105
Source: PubMed


Contraction of the heart results from interaction of the myosin and actin filaments. Cardiac myosin filaments consist of the molecular motor myosin II, the sarcomeric template protein, titin, and the cardiac modulatory protein, myosin binding protein C (MyBP-C). Inherited hypertrophic cardiomyopathy (HCM) is a disease caused mainly by mutations in these proteins. The structure of cardiac myosin filaments and the alterations caused by HCM mutations are unknown. We have used electron microscopy and image analysis to determine the three-dimensional structure of myosin filaments from wild-type mouse cardiac muscle and from a MyBP-C knockout model for HCM. Three-dimensional reconstruction of the wild-type filament reveals the conformation of the myosin heads and the organization of titin and MyBP-C at 4 nm resolution. Myosin heads appear to interact with each other intramolecularly, as in off-state smooth muscle myosin [Wendt T, Taylor D, Trybus KM, Taylor K (2001) Proc Natl Acad Sci USA 98:4361-4366], suggesting that all relaxed muscle myosin IIs may adopt this conformation. Titin domains run in an elongated strand along the filament surface, where they appear to interact with part of MyBP-C and with the myosin backbone. In the knockout filament, some of the myosin head interactions are disrupted, suggesting that MyBP-C is important for normal relaxation of the filament. These observations provide key insights into the role of the myosin filament in cardiac contraction, assembly, and disease. The techniques we have developed should be useful in studying the structural basis of other myosin-related HCM diseases.

Download full-text


Available from: Roger Craig,
  • Source
    • "Hence, MyBP-C appears essential for normal cardiac functioning. In cardiac thick filaments from knockout mice, the interaction between some of the myosin heads was disrupted [32] [38] and the intensity ratio of the X-ray equatorial reflections suggested that the myosin heads lay further out from the thick filament backbone [40]. Thus, one function of MyBP-C might be to interact with myosin heads near the head–tail junction and tether them closer to the backbone. "

    Journal of Molecular Biology 11/2014; 427(2). DOI:10.1016/j.jmb.2014.11.006 · 4.33 Impact Factor
  • Source
    • "Much of the biochemistry can be explained by an asymmetric, intramolecular interaction between the two-myosin heads, first visualized by cryoelectron microscopy (cryoEM) of 2-D arrays of dephosphorylated smHMM (Wendt et al., 2001). Subsequently, this motif was also identified in thick filaments from three striated muscles (Woodhead et al., 2005; Zhao et al., 2009; Zoghbi et al., 2008), as well as in electron micrographs of negatively stained single molecules of myosin II isoforms from several species (Burgess et al., 2007; Jung et al., 2008a). The near ubiquitous presence of this intramolecular myosin head–head interaction has led to the suggestion that it is both an ancient and general mechanism for myosin II inhibition (Jung et al., 2008a,b). "
    [Show abstract] [Hide abstract]
    ABSTRACT: The activity of smooth and non-muscle myosin II is regulated by phosphorylation of the regulatory light chain (RLC) at serine 19. The dephosphorylated state of full-length monomeric myosin is characterized by an asymmetric intramolecular head-head interaction that completely inhibits the ATPase activity, accompanied by a hairpin fold of the tail, which prevents filament assembly. Phosphorylation of serine 19 disrupts these head-head interactions by an unknown mechanism. Computational modeling (Tama et al., 2005. J. Mol. Biol.345, 837-854) suggested that formation of the inhibited state is characterized by both torsional and bending motions about the myosin heavy chain (HC) at a location between the RLC and the essential light chain (ELC). Therefore, altering relative motions between the ELC and the RLC at this locus might disrupt the inhibited state. Based on this hypothesis we have derived an atomic model for the phosphorylated state of the smooth muscle myosin light chain domain (LCD). This model predicts a set of specific interactions between the N-terminal residues of the RLC with both the myosin HC and the ELC. Site directed mutagenesis was used to show that interactions between the phosphorylated N-terminus of the RLC and helix-A of the ELC are required for phosphorylation to activate smooth muscle myosin.
    Journal of Structural Biology 12/2013; 106(2). DOI:10.1016/j.jsb.2013.12.008 · 3.23 Impact Factor
  • Source
    • "However, they could not definitively demonstrate the nature of the perturbation, nor produced a detailed 3D structure of the myosin filaments in vertebrate striated muscles. Single particle image analysis of EM images been successfully used on myosin filaments isolated from fish skeletal muscle,22,55,56 rabbit heart muscle,23 mouse heart muscles25 and most recently myosin filaments from human heart muscles.24,57 "
    [Show abstract] [Hide abstract]
    ABSTRACT: High resolution information about the three-dimensional (3D) structure of myosin filaments has always been hard to obtain. Solving the 3D structure of myosin filaments is very important because mutations in human cardiac muscle myosin and its associated proteins (e.g. titin and myosin binding protein C) are known to be associated with a number of familial human cardiomyopathies (e.g. hypertrophic cardiomyopathy and dilated cardiomyopathy). In order to understand how normal heart muscle works and how it fails, as well as the effects of the known mutations on muscle contractility, it is essential to properly understand myosin filament 3D structure and properties in both healthy and diseased hearts. The aim of this review is firstly to provide a general overview of the 3D structure of myosin thick filaments, as studied so far in both vertebrates and invertebrate striated muscles. Knowledge of this 3D structure is the starting point from which myosin filaments isolated from human cardiomyopathic samples, with known mutations in either myosin or its associated proteins (titin or C-protein), can be studied in detail. This should, in turn, enable us to relate the structure of myosin thick filament to its function and to understanding the disease process. A long term objective of this research would be to assist the design of possible therapeutic solutions to genetic myosin-related human cardiomyopathies.
    11/2013; 2013(3):280-302. DOI:10.5339/gcsp.2013.36
Show more