Direct recording of myosin head power and recovery strokes in hydrated myosin filaments provides evidence against the swinging lever arm mechanism in muscle contraction

Clear images of myosin filaments have been seen in shadowed freeze-fracture replicas of single fibers of relaxed frog semitendinosus muscles rapidly frozen using a dual propane jet freezing device. These images have been analyzed by optical diffraction and computer averaging and have been modelled to reveal details of the myosin head configuration on the right-handed, three-stranded helix of cross-bridges. Both the characteristic 430-A and 140-150-A repeats of the myosin cross-bridge array could be seen. The measured filament backbone diameter was 140-160 A, and the outer diameter of the cross-bridge array was 300 A. Evidence is presented that suggests that the observed images are consistent with a model in which both of the heads of one myosin molecule tilt in the same direction at an angle of approximately 50-70 degrees to the normal to the filament long axis and are slewed so that they lie alongside each other and their radially projected density lies along the three right-handed helical tracks. Any perturbation of the myosin heads away from their ideal lattice sites needed to account for x-ray reflections not predicted for a perfect helix must be essentially along the three helical tracks of cross-bridges. Little trace of the presence of non-myosin proteins could be seen.

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Defects in the Existing Theory of Skeletal Muscle Contraction and Postulation of a New Theory

European Journal of Medical and Health Sciences ◽

10.24018/ejmed.2020.2.6.573 ◽

2020 ◽

Vol 2 (6) ◽

Author(s):

O. Sasikumari

Keyword(s):

Skeletal Muscle ◽

Muscle Contraction ◽

Massachusetts Institute Of Technology ◽

Research Teams ◽

University Of Cambridge ◽

Skeletal Muscle Contraction ◽

Myosin Filaments ◽

Institute Of Technology ◽

Sliding Filament Theory ◽

The University

In 1954 , two independent research teams, one consisting of Andrew F. Huxley and Rolf Niedergerke from the University of Cambridge, and the other consisting of Hugh Huxley and Jean Hanson from the Massachusetts Institute of Technology proposed the theory of skeletal muscle contraction [1]. They used electron microscopy to study the details of muscle filaments. The structure was studied in detail by then, but the mechanism of skeletal muscle contraction was not defined. Based on various assumptions about the actin and myosin filaments of muscle, later they postulated a theory called “sliding filament theory”. When this theory is scrutinized in detail, I find that there are a lot of defects in this theory, which I have pointed out and I have made an attempt to postulate a different mechanism for the skeletal muscle contraction.

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Evidence for the Essential Role of Myosin Subfragment-2 in Muscle Contraction: Functional Communication between Myosin Head and Subfragment-2

Journal of Material Science & Engineering ◽

10.4172/2169-0022.1000386 ◽

2017 ◽

Vol 06 (05) ◽

Cited By ~ 1

Author(s):

Haruo Sugi

Keyword(s):

Muscle Contraction ◽

Essential Role ◽

Myosin Head ◽

Functional Communication ◽

Myosin Subfragment

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X-ray Diffraction Studies on the Structural Origin of Dynamic Tension Recovery Following Ramp-Shaped Releases in High-Ca Rigor Muscle Fibers

International Journal of Molecular Sciences ◽

10.3390/ijms21041244 ◽

2020 ◽

Vol 21 (4) ◽

pp. 1244

Author(s):

Haruo Sugi ◽

Maki Yamaguchi ◽

Tetsuo Ohno ◽

Hiroshi Okuyama ◽

Naoto Yagi

Keyword(s):

Muscle Contraction ◽

Actin Filaments ◽

Myosin Head ◽

Muscle Fibers ◽

Skinned Fibers ◽

Myosin Filament ◽

X Ray Diffraction ◽

X Ray ◽

Tension Recovery ◽

Pass Through

It is generally believed that during muscle contraction, myosin heads (M) extending from myosin filament attaches to actin filaments (A) to perform power stroke, associated with the reaction, A-M-ADP-Pi → A-M + ADP + Pi, so that myosin heads pass through the state of A-M, i.e., rigor A-M complex. We have, however, recently found that: (1) an antibody to myosin head, completely covering actin-binding sites in myosin head, has no effect on Ca2+-activated tension in skinned muscle fibers; (2) skinned fibers exhibit distinct tension recovery following ramp-shaped releases (amplitude, 0.5% of Lo; complete in 5 ms); and (3) EDTA, chelating Mg ions, eliminate the tension recovery in low-Ca rigor fibers but not in high-Ca rigor fibers. These results suggest that A-M-ADP myosin heads in high-Ca rigor fibers have dynamic properties to produce the tension recovery following ramp-shaped releases, and that myosin heads do not pass through rigor A-M complex configuration during muscle contraction. To obtain information about the structural changes in A-M-ADP myosin heads during the tension recovery, we performed X-ray diffraction studies on high-Ca rigor skinned fibers subjected to ramp-shaped releases. X-ray diffraction patterns of the fibers were recorded before and after application of ramp-shaped releases. The results obtained indicate that during the initial drop in rigor tension coincident with the applied release, rigor myosin heads take up applied displacement by tilting from oblique to perpendicular configuration to myofilaments, and after the release myosin heads appear to rotate around the helical structure of actin filaments to produce the tension recovery.

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Muscle myosins form folded monomers, dimers, and tetramers during filament polymerization in vitro

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2001892117 ◽

2020 ◽

Vol 117 (27) ◽

pp. 15666-15672

Author(s):

Xiong Liu ◽

Shi Shu ◽

Edward D. Korn

Keyword(s):

Electron Microscopy ◽

Smooth Muscle ◽

Muscle Contraction ◽

Actin Filaments ◽

Critical Concentration ◽

Smooth Muscle Myosin ◽

Myosin Filaments ◽

Muscle Myosin

Muscle contraction depends on the cyclical interaction of myosin and actin filaments. Therefore, it is important to understand the mechanisms of polymerization and depolymerization of muscle myosins. Muscle myosin 2 monomers exist in two states: one with a folded tail that interacts with the heads (10S) and one with an unfolded tail (6S). It has been thought that only unfolded monomers assemble into bipolar and side-polar (smooth muscle myosin) filaments. We now show by electron microscopy that, after 4 s of polymerization in vitro in both the presence (smooth muscle myosin) and absence of ATP, skeletal, cardiac, and smooth muscle myosins form tail-folded monomers without tail–head interaction, tail-folded antiparallel dimers, tail-folded antiparallel tetramers, unfolded bipolar tetramers, and small filaments. After 4 h, the myosins form thick bipolar and, for smooth muscle myosin, side-polar filaments. Nonphosphorylated smooth muscle myosin polymerizes in the presence of ATP but with a higher critical concentration than in the absence of ATP and forms only bipolar filaments with bare zones. Partial depolymerization in vitro of nonphosphorylated smooth muscle myosin filaments by the addition of MgATP is the reverse of polymerization.

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