scholarly journals Myosin molecule packing within the vertebrate skeletal muscle thick filaments. A complete bipolar model.

2002 ◽  
Vol 49 (4) ◽  
pp. 829-840 ◽  
Author(s):  
Ludmila Skubiszak ◽  
Leszek Kowalczyk
Keyword(s):  
Skeletal Muscle ◽  
Computer Modelling ◽  
Thick Filament ◽  
Myosin Molecule ◽  
Bipolar Structure ◽  
Cross Bridge ◽  
Filament Axis ◽  
Thick Filaments ◽  
C Terminus ◽  
Vertebrate Skeletal Muscle

Computer modelling related to the real dimensions of both the whole filament and the myosin molecule subfragments has revealed two alternative modes for myosin molecule packing which lead to the head disposition similar to that observed by EM on the surface of the cross-bridge zone of the relaxed vertebrate skeletal muscle thick filaments. One of the modes has been known for three decades and is usually incorporated into the so-called three-stranded model. The new mode differs from the former one in two aspects: (1) myosin heads are grouped into asymmetrical cross-bridge crowns instead of symmetrical ones; (2) not the whole myosin tail, but only a 43-nm C-terminus of each of them is straightened and near-parallel to the filament axis, the rest of the tail is twisted. Concurrent exploration of these alternative modes has revealed their influence on the filament features. The parameter values for the filament models as well as for the building units depicting the myosin molecule subfragments are verified by experimental data found in the literature. On the basis of the new mode for myosin molecule packing a complete bipolar structure of the thick filament is created.

scholarly journals The vertebrate skeletal muscle thick filaments are not three-stranded. Reinterpretation of some experimental data.

2002 ◽  
Vol 49 (4) ◽  
pp. 841-853 ◽  
Author(s):  
Ludmila Skubiszak ◽  
Leszek Kowalczyk
Keyword(s):  
Skeletal Muscle ◽  
Mass Distribution ◽  
Thick Filament ◽  
X Ray Diffraction ◽  
Bipolar Structure ◽  
X Ray ◽  
Thick Filaments ◽  
Diffraction Patterns ◽  
Cross Bridges ◽  
Vertebrate Skeletal Muscle

Computer simulation of mass distribution within the model and Fourier transforms of images depicting mass distribution are explored for verification of two alternative modes of the myosin molecule arrangement within the vertebrate skeletal muscle thick filaments. The model well depicting the complete bipolar structure of the thick filament and revealing a true threefold-rotational symmetry is a tube covered by two helices with a pitch of 2 x 43 nm due to arrangement of the myosin tails along a helical path and grouping of all myosin heads in the crowns rotated by 240 degrees and each containing three cross-bridges separated by 0 degrees, 120 degrees, and 180 degrees. The cross-bridge crown parameters are verified by EM images as well as by optical and low-angle X-ray diffraction patterns found in the literature. The myosin tail arrangement, at which the C-terminus of about 43-nm length is near-parallel to the filament axis and the rest of the tail is quite strongly twisted around, is verified by the high-angle X-ray diffraction patterns. A consequence of the new packing is a new way of movement of the myosin cross-bridges, namely, not by bending in the hinge domains, but by unwrapping from the thick filament surface towards the thin filaments along a helical path.

scholarly journals Dynamics of myosin replacement in skeletal muscle cells

2015 ◽  
Vol 309 (10) ◽  
pp. C669-C679 ◽  
Author(s):  
Koichi Ojima ◽  
Emi Ichimura ◽  
Yuya Yasukawa ◽  
Jun-ichi Wakamatsu ◽  
Takanori Nishimura
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Dynamic Equilibrium ◽  
Muscle Cells ◽  
Thick Filament ◽  
Skeletal Muscle Cells ◽  
Myosin Molecule ◽  
Thick Filaments ◽  
Cultured Myotubes ◽  
Exchange Unit

Highly organized thick filaments in skeletal muscle cells are formed from ∼300 myosin molecules. Each thick-filament-associated myosin molecule is thought to be constantly exchanged. However, the mechanism of myosin replacement remains unclear, as does the source of myosin for substitution. Here, we investigated the dynamics of myosin exchange in the myofibrils of cultured myotubes by fluorescent recovery after photobleaching and found that myofibrillar myosin is actively replaced with an exchange half-life of ∼3 h. Myosin replacement was not disrupted by the absence of the microtubule system or by actomyosin interactions, suggesting that known cytoskeletal systems are dispensable for myosin substitution. Intriguingly, myosin replacement was independent of myosin binding protein C, which links myosin molecules together to form thick filaments. This implies that an individual myosin molecule rather than a thick filament functions as an exchange unit. Furthermore, the myosin substitution rate was decreased by the inhibition of protein synthesis, suggesting that newly synthesized myosin, as well as preexisting cytosolic myosin, contributes to myosin replacement in myofibrils. Notably, incorporation and release of myosin occurred simultaneously in myofibrils, but rapid myosin release from myofibrils was observed without protein synthesis. Collectively, our results indicate that myosin shuttles between myofibrils and the nonmyofibrillar cytosol to maintain a dynamic equilibrium in skeletal muscle cells.

An ultrastructural study of crossbridge arrangement in the fish skeletal muscle thick filament

1989 ◽  
Vol 94 (3) ◽  
pp. 391-401
Author(s):  
R.W. Kensler ◽  
M. Stewart
Keyword(s):  
Skeletal Muscle ◽  
Fourier Transforms ◽  
Thick Filament ◽  
Fish Muscle ◽  
X Ray Diffraction ◽  
X Ray ◽  
Thick Filaments ◽  
Gold Fish ◽  
Diffraction Patterns ◽  
Cross Bridges

A procedure has been developed for isolating gold-fish skeletal muscle thick filaments that preserves the near-helical arrangement of the myosin cross-bridges under relaxing conditions. These filaments have been examined by electron microscopy and computer image analysis. Electron micrographs of the negatively stained filaments showed a clear periodicity associated with the crossbridges, with an axial repeat every 42.9 nm. Computed Fourier transforms of the negatively stained filaments showed a series of layer lines confirming this periodicity, and were similar to the X-ray diffraction patterns of fish muscle obtained by J. Hartford and J. Squire. Analysis of the computed transform data and filtered images of the isolated fish filaments demonstrated that the myosin crossbridges lie along three strands. Platinum shadowing demonstrated that the strands have a right-handed orientation, and computed transforms and filtered images of the shadowed filaments suggest that the crossbridges are perturbed both axially and azimuthally from an ideal helical arrangement.

scholarly journals Elastic behavior of connectin filaments during thick filament movement in activated skeletal muscle.

1989 ◽  
Vol 109 (5) ◽  
pp. 2169-2176 ◽  
Author(s):  
R Horowits ◽  
K Maruyama ◽  
R J Podolsky
Keyword(s):  
Skeletal Muscle ◽  
Calcium Ions ◽  
Striated Muscle ◽  
Muscle Protein ◽  
Thick Filament ◽  
Elastic Behavior ◽  
Constant Length ◽  
Thick Filaments ◽  
Band Spacing ◽  
Antibody Label

Connectin (also called titin) is a huge, striated muscle protein that binds to thick filaments and links them to the Z-disc. Using an mAb that binds to connectin in the I-band region of the molecule, we studied the behavior of connectin in both relaxed and activated skinned rabbit psoas fibers by immunoelectron microscopy. In relaxed fibers, antibody binding is visualized as two extra striations per sarcomere arranged symmetrically about the M-line. These striations move away from both the nearest Z-disc and the thick filaments when the sarcomere is stretched, confirming the elastic behavior of connectin within the I-band of relaxed sarcomeres as previously observed by several investigators. When the fiber is activated, thick filaments in sarcomeres shorter than 2.8 microns tend to move from the center to the side of the sarcomere. This translocation of thick filaments within the sarcomere is accompanied by movement of the antibody label in the same direction. In that half-sarcomere in which the thick filaments move away from the Z-disc, the spacings between the Z-disc and the antibody and between the antibody and the thick filaments both increase. Conversely, on the side of the sarcomere in which the thick filaments move nearer to the Z-line, these spacings decrease. Regardless of whether I-band spacing is varied by stretch of a relaxed sarcomere or by active sliding of thick filaments within a sarcomere of constant length, the spacings between the Z-line and the antibody and between the antibody and the thick filaments increase with I-band length identically. These results indicate that the connectin filaments remain bound to the thick filaments in active fibers, and that the elastic properties of connectin are unaltered by calcium ions and cross-bridge activity.

scholarly journals Dependence of thick filament structure in relaxed mammalian skeletal muscle on temperature and interfilament spacing

2021 ◽  
Vol 153 (3) ◽  
Author(s):  
Marco Caremani ◽  
Luca Fusi ◽  
Marco Linari ◽  
Massimo Reconditi ◽  
Gabriella Piazzesi ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Thick Filament ◽  
Structural Basis ◽  
Mammalian Skeletal Muscle ◽  
X Ray ◽  
Physiological Temperature ◽  
Thick Filaments ◽  
Filament Structure ◽  
Intact Muscle ◽  
Resting Muscle

Contraction of skeletal muscle is regulated by structural changes in both actin-containing thin filaments and myosin-containing thick filaments, but myosin-based regulation is unlikely to be preserved after thick filament isolation, and its structural basis remains poorly characterized. Here, we describe the periodic features of the thick filament structure in situ by high-resolution small-angle x-ray diffraction and interference. We used both relaxed demembranated fibers and resting intact muscle preparations to assess whether thick filament regulation is preserved in demembranated fibers, which have been widely used for previous studies. We show that the thick filaments in both preparations exhibit two closely spaced axial periodicities, 43.1 nm and 45.5 nm, at near-physiological temperature. The shorter periodicity matches that of the myosin helix, and x-ray interference between the two arrays of myosin in the bipolar filament shows that all zones of the filament follow this periodicity. The 45.5-nm repeat has no helical component and originates from myosin layers closer to the filament midpoint associated with the titin super-repeat in that region. Cooling relaxed or resting muscle, which partially mimics the effects of calcium activation on thick filament structure, disrupts the helical order of the myosin motors, and they move out from the filament backbone. Compression of the filament lattice of demembranated fibers by 5% Dextran, which restores interfilament spacing to that in intact muscle, stabilizes the higher-temperature structure. The axial periodicity of the filament backbone increases on cooling, but in lattice-compressed fibers the periodicity of the myosin heads does not follow the extension of the backbone. Thick filament structure in lattice-compressed demembranated fibers at near-physiological temperature is similar to that in intact resting muscle, suggesting that the native structure of the thick filament is largely preserved after demembranation in these conditions, although not in the conditions used for most previous studies with this preparation.

Sign in / Sign up

Export Citation Format

Share Document