scholarly journals Muscle contraction as a Markov Process - II: x-ray interference data (M3 & M6 reflections) imply myosin cross-bridge motions are controlled by structural transitions along actin filaments

2021 ◽  
Author(s):  
Clarence E Schutt ◽  
Vladimir Gelfand ◽  
Eli Paster
Keyword(s):  
Muscle Contraction ◽  
Actin Filaments ◽  
Myosin Head ◽  
Muscle Fibers ◽  
Head Movements ◽  
Published Data ◽  
Structural Transitions ◽  
X Ray ◽  
Thick Filaments ◽  
In Series

AbstractThe unit underlying the construction and functioning of muscle fibers is the sarcomere. Tension develops in fibers as thousands of sarcomeres arranged in series contract in unison. Shortening is due to the sliding of actin thin filaments along antiparallel arrays of myosin thick filaments. Remarkably, myosin catalytic heads situated across the center M-line of a sarcomere are separated by a distance that is a half integral of the 14.5 nm spacing between successive layers of myosin heads on the thick filaments. This results in the splitting of the 14.5 nm meridional reflection in X-ray diffraction patterns of muscle fibers. Following a quick drop in tension, changes in the relative intensities of the split meridional peaks provide a sensitive measure of myosin head movements. We use published data obtained with the x-ray interference method to validate a theory of muscle contraction in which cooperative structural transitions along force-generating actin filaments regulate the binding of myosin heads. The probability that an actin-bound myosin head will detach is represented here by a statistical function that yields a length-tension curve consistent with classical descriptions of the recovery of contracting muscle fibers subjected to millisecond drops in tension.

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

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.

scholarly journals Resting myosin cross-bridge configuration in frog muscle thick filaments.

1986 ◽  
Vol 102 (2) ◽  
pp. 610-618 ◽  
Author(s):  
M Cantino ◽  
J Squire
Keyword(s):  
Myosin Head ◽  
Freeze Fracture ◽  
Optical Diffraction ◽  
Outer Diameter ◽  
X Ray ◽  
Cross Bridge ◽  
Thick Filaments ◽  
Myosin Filaments ◽  
Cross Bridges ◽  
The Right

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.

scholarly journals X-ray diffraction analysis of the effects of myosin regulatory light chain phosphorylation and butanedione monoxime on skinned skeletal muscle fibers

2016 ◽  
Vol 310 (8) ◽  
pp. C692-C700 ◽  
Author(s):  
Maki Yamaguchi ◽  
Masako Kimura ◽  
Zhao-bo Li ◽  
Tetsuo Ohno ◽  
Shigeru Takemori ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Light Chain ◽  
Muscle Fibers ◽  
Structural Basis ◽  
Myosin Regulatory Light Chain ◽  
X Ray Diffraction ◽  
Phosphate Release ◽  
X Ray ◽  
Thick Filaments ◽  
Butanedione Monoxime

The phosphorylation of the myosin regulatory light chain (RLC) is an important modulator of skeletal muscle performance and plays a key role in posttetanic potentiation and staircase potentiation of twitch contractions. The structural basis for these phenomena within the filament lattice has not been thoroughly investigated. Using a synchrotron radiation source at SPring8, we obtained X-ray diffraction patterns from skinned rabbit psoas muscle fibers before and after phosphorylation of myosin RLC in the presence of myosin light chain kinase, calmodulin, and calcium at a concentration below the threshold for tension development ([Ca2+] = 10−6.8 M). After phosphorylation, the first myosin layer line slightly decreased in intensity at ∼0.05 nm−1 along the equatorial axis, indicating a partial loss of the helical order of myosin heads along the thick filament. Concomitantly, the (1,1/1,0) intensity ratio of the equatorial reflections increased. These results provide a firm structural basis for the hypothesis that phosphorylation of myosin RLC caused the myosin heads to move away from the thick filaments towards the thin filaments, thereby enhancing the probability of interaction with actin. In contrast, 2,3-butanedione monoxime (BDM), known to inhibit contraction by impeding phosphate release from myosin, had exactly the opposite effects on meridional and equatorial reflections to those of phosphorylation. We hypothesize that these antagonistic effects are due to the acceleration of phosphate release from myosin by phosphorylation and its inhibition by BDM, the consequent shifts in crossbridge equilibria leading to opposite changes in abundance of the myosin-ADP-inorganic phosphate complex state associated with helical order of thick filaments.

scholarly journals Stabilization of the Central Part of Tropomyosin Molecule Alters the Ca 2+-sensitivity of Actin-Myosin Interaction

Acta Naturae ◽  
2013 ◽  
Vol 5 (3) ◽  
pp. 126-129 ◽  
Author(s):  
D. V. Shchepkin ◽  
A. M. Matyushenko ◽  
G. V. Kopylova ◽  
N. V. Artemova ◽  
S. Y. Bershitsky ◽  
...  
Keyword(s):  
Actin Filaments ◽  
Myosin Head ◽  
Motility Assay ◽  
Published Data ◽  
Physiological Effects ◽  
Sliding Velocity ◽  
In Vitro Motility Assay ◽  
In Vitro Motility ◽  
Myosin Interaction

We show that the mutations D137L and G126R, which stabilize the central part of the tropomyosin (Tm) molecule, increase both the maximal sliding velocity of the regulated actin filaments in the in vitro motility assay at high Са 2+ concentrations and the Са 2+-sensitivity of the actin-myosin interaction underlying this sliding. Based on an analysis of the recently published data on the structure of the actin-Tmmyosin complex, we suppose that the physiological effects of these mutations in Tm can be accounted for by their influence on the interactions between the central part of Tm and certain sites of the myosin head.

Orientation of actin filaments during motion in motility assay

1995 ◽  
Vol 53 ◽  
pp. 52-53
Author(s):  
J. Borejdo ◽  
S. Burlacu
Keyword(s):  
Actin Filaments ◽  
Thin Filament ◽  
Striated Muscle ◽  
Myosin Head ◽  
Classical Method ◽  
Polarization Of Fluorescence ◽  
Single Protein ◽  
Intracellular Organelles ◽  
Change Orientation ◽  
Active Entity

Polarization of fluorescence is a classical method to assess orientation or mobility of macromolecules. It has been a common practice to measure polarization of fluorescence through a microscope to characterize orientation or mobility of intracellular organelles, for example anisotropic bands in striated muscle. Recently, we have extended this technique to characterize single protein molecules. The scientific question concerned the current problem in muscle motility: whether myosin heads or actin filaments change orientation during contraction. The classical view is that the force-generating step in muscle is caused by change in orientation of myosin head (subfragment-1 or SI) relative to the axis of thin filament. The molecular impeller which causes this change resides at the interface between actin and SI, but it is not clear whether only the myosin head or both SI and actin change orientation during contraction. Most studies assume that observed orientational change in myosin head is a reflection of the fact that myosin is an active entity and actin serves merely as a passive "rail" on which myosin moves.

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