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Evidence for structural changes in crossbridges during force generation

B Brenner1, L C Yu

  • 1Department of General Physiology, University of Ulm, Germany.

Advances in Experimental Medicine and Biology
|January 1, 1993
PubMed
Summary
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Myosin crossbridge conformations during muscle contraction were studied using X-ray diffraction. Force-generating crossbridges exhibit a distinct structure, differing from both weakly attached and rigor states.

Area of Science:

  • Muscle Physiology
  • Biophysics
  • Structural Biology

Background:

  • Muscle contraction involves myosin heads interacting with actin.
  • The precise conformational changes of myosin crossbridges during force generation remain debated.
  • Previous studies suggest large conformational shifts, but direct evidence for attached crossbridges is ambiguous.

Purpose of the Study:

  • To investigate and compare the conformations of attached myosin crossbridges in different functional states.
  • To differentiate the structural states of crossbridges before force generation, during force generation, and in rigor.

Main Methods:

  • High-resolution equatorial X-ray diffraction patterns were collected from single chemically skinned rabbit psoas muscle fibers.
  • Experiments were conducted under relaxed (pre-force generating), Ca(2+)-activated (force generating), and rigor conditions.

Related Experiment Videos

  • Specific ionic strength (50 mM) and temperature (5°C) ensured high crossbridge attachment in all states.

    • Main Results:

    • Changes in X-ray diffraction intensities (I10 and I11) upon activation differed from expected reciprocal changes.
    • Intensity I11 showed minimal change, while I10 decreased by 30% upon activation.
    • Significant changes in I10 were also observed when transitioning from the activated to the rigor state.
    • Higher-order reflections indicated unique structures for force-generating crossbridges.

    Conclusions:

    • The average conformation of force-generating crossbridges is distinct from weakly attached and rigor crossbridges.
    • This study provides direct evidence challenging the notion of a simple mixture of states during force generation.
    • The findings offer new insights into the structural dynamics of myosin during muscle contraction.