Axial Disposition of Myosin Heads in Isometrically Contracting Muscles

Juanhuix, Jordi; Bordas, J.; Campmany, J.; Svensson, Arne; Bassford, Marie; Narayanan, Theyencheri

doi:10.1016/s0006-3495(01)76115-2

Cited by 43 publications

(40 citation statements)

References 29 publications

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“…For example, as the M3 reflection during isometric contraction is split into two peaks of comparable intensity, say the n th and the (n+1) th order of the interference distance, almost equidistant from the centre of M3, then at the level of the M6 reflection (the 2 nd order of the M3) the 2n th and the (2n+2) th order should still be almost equidistant from the centre of the reflection, with the (2n+1) th order sampling the M6 close to its centre and the satellite peaks of about 0.1 its intensity. This is not the case, as the M6 is still sampled by two unequal peaks but with an intensity ratio much higher than expected (ratio HA/LA peaks about 0.5; Juanhuix et al 2001). Thus, the fine structure of the meridional reflections seems to originate from a slightly different interference distance because the diffractor, the myosin head, is asymmetric along the meridional axis.…”

Section: The Interference Effect Provides the Phase Informationmentioning

confidence: 81%

Recent improvements in small angle x-ray diffraction for the study of muscle physiology

Reconditi¹

2006

Rep. Prog. Phys.

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The molecular mechanism of muscle contraction is one of the most important unresolved problems in Biology and Biophysics. Notwithstanding the great advances of recent years, it is not yet known in detail how the molecular motor in muscle, the class II myosin, converts the free energy of ATP hydrolysis into work by interacting with its track, the actin filament, neither it is understood how the high efficiency in energy conversion depends on the cooperative action of myosin motors working in parallel along the actin filament. Researches in muscle contraction imply the combination of mechanical, biochemical and structural methods in studies that span from tissue to single molecule. Therefore, more than for any other research field, progresses in the comprehension of muscle contraction at molecular level are related to, and in turn contribute to, the advancement of methods in Biophysics.This review will focus on the progresses achieved by time resolved small angle X-ray scattering (SAXS) from muscle, an approach made possible by the highly ordered arrangement of both the contractile proteins myosin and actin in the ca 2 μm long structural unit the sarcomere that repeats along the whole length of the muscle cell. Among the time resolved structural techniques, SAXS has proved to be the most powerful method of investigation, as it allows the molecular motor to be studied in situ, in intact single muscle cells, where it is possible to combine the structural study with fast mechanical methods that synchronize the action of the molecular motors. The latest development of this technique allows Angstrom-scale measurements of the axial movement of the motors that pull the actin filament toward the centre of the sarcomere, by exploiting the X-ray interference between the two arrays of myosin motors in the two halves of the sarcomere.

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Section: The Interference Effect Provides the Phase Informationmentioning

confidence: 81%

Recent improvements in small angle x-ray diffraction for the study of muscle physiology

Reconditi¹

2006

Rep. Prog. Phys.

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“…3), (c) the distribution and mass of any heads not attached to actin and (d) any contributions from accessory proteins such as Cprotein. Since the meridional contribution from Cprotein appears to be very weak in patterns from active muscle, 6,25 we assume here that the M3 and M6 intensity changes during transients will depend primarily on the changing contributions to these peaks from the detached and attached myosin head populations.…”

Section: Contributors To the M3 And M6 Peaksmentioning

confidence: 99%

Probing Muscle Myosin Motor Action: X-Ray (M3 and M6) Interference Measurements Report Motor Domain Not Lever Arm Movement

Knupp

Offer

Ranatunga

et al. 2009

Journal of Molecular Biology

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“…Such a steeper relation might result from a longer lever (33) or structural changes in and/or tilting of the motor domain (32). Figure 5 differs from a previous double-headed structure proposed by Juanhuix et al (23). That structure was based on both S1s having rigor conformations, while we have assumed this conformation to be reached only at the end of the power stroke.…”

Section: Discussionmentioning

confidence: 73%

“…That structure was based on both S1s having rigor conformations, while we have assumed this conformation to be reached only at the end of the power stroke. In addition, the Juanhuix et al (23) structure was deduced from interference effects between opposite halves of the sarcomere in several harmonics of M3, but it is possible that some of these reflections arise from structures other than S1, because not all of them respond to length steps with a change in intensity (20). For the free head be ordered when its partner is actin bound, there must be communication between the heads of the myosin dimer.…”

Section: Discussionmentioning

confidence: 99%

Myosin lever disposition during length oscillations when power stroke tilting is reduced

Griffiths

Bagni²,

Colombini³

et al. 2005

American Journal of Physiology-Cell Physiology

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(I M3) from tetanized, intact skeletal muscle fiber bundles was measured during sinusoidal length oscillations at 2.8 kHz, a frequency at which the myosin motor's power stroke is greatly reduced. I M3 signals were approximately sinusoidal, but showed a "double peak" distortion previously observed only at lower oscillation frequencies. A tilting lever arm model simulated this distortion, where I M3 was calculated from the molecular structure of myosin subfragment 1 (S1). Simulations showed an isometric lever arm disposition close to normal to the filament axis at isometric tension, similar to that found using lower oscillation frequencies, where the power stroke contributes more toward total S1 movement. Inclusion of a second detached S1 in each actin-bound myosin dimer increased simulated I M3 signal amplitude and improved agreement with the experimental data. The best agreement was obtained when detached heads have a fixed orientation, insensitive to length changes, and similar to that of attached heads at tetanus plateau. This configuration also accounts for the variations in relative intensity of the two main peaks of the M3 reflection substructure after a length change. This evidence of an I M3 signal distortion when power stroke tilting is suppressed, provided that a large enough amplitude of length oscillation is used, is consistent with the tilting lever arm model of the power stroke. skeletal muscle; X-ray diffraction; muscle mechanics; molecular motors; subfragment 1 structure MYOSIN MOTORS are intracellular protein macromolecules, which function as actin-dependent transducers of ATP hydrolysis free energy into mechanical work. At least 17 classes of myosin exist, fulfilling many important motile roles in cell physiology, including cell division, cytokinesis, exo-, endo-, and pinocytosis, acuity adjustment of sensory receptors, and the contraction of all forms of muscle tissue (34). Their mechanism is thought to involve the active tilting (power stroke) of the myosin lever arm domain [a 9-nm-long projection from the actin-and ATP-binding motor domain of myosin subfragment 1 (S1)] during ATP cleavage at the motor domain's catalytic site (17, 31). Tilting displaces the arm's tip, producing a ϳ4-to 10-nm translational movement or 2-4 pN of force (7,27). A feature unique among myosin motors is that striated muscle myosin (myosin II) aggregates into highly structured filaments aligned within a quasicrystalline lattice, which yield a characteristic X-ray diffraction pattern (18) and the intensity of the 14.55 nm meridional X-ray reflection (I M3 ) is thought to be sensitive to lever arm tilting (21). This is because I M3 depends on the density of the S1 mass projected onto the filament axis, which changes with lever arm tilting. The maximum I M3 (I M3,max ) is reached when the lever is roughly perpendicular to the filament because at this point the axially projected mass distribution is at its most concentrated. In isometrically activated muscle, I M3 increases to a maximum for a small filament displacement ...

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Axial Disposition of Myosin Heads in Isometrically Contracting Muscles

Cited by 43 publications

References 29 publications

Recent improvements in small angle x-ray diffraction for the study of muscle physiology

Recent improvements in small angle x-ray diffraction for the study of muscle physiology

Probing Muscle Myosin Motor Action: X-Ray (M3 and M6) Interference Measurements Report Motor Domain Not Lever Arm Movement

Myosin lever disposition during length oscillations when power stroke tilting is reduced

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