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Visualizing myosin's power stroke in muscle contraction.

¹Department of Cell Biology, Duke University Medical Center, Durham, NC 27710, USA. mary.reedy@cellbio.duke.edu

Journal of Cell Science

|October 6, 2000

Summary

Recent studies support the swinging crossbridge hypothesis for myosin motor action. Evidence from insect flight muscle and fiber experiments shows lever arm movements linked to force changes during muscle contraction.

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Area of Science:

Muscle Physiology
Biophysics
Molecular Motor Mechanisms

Background:

The swinging crossbridge/lever arm hypothesis explains myosin head motor function.
Previous models lacked direct experimental validation of dynamic movements during contraction.

Purpose of the Study:

To provide direct evidence for the swinging crossbridge hypothesis.
To elucidate the atomic-level mechanism of myosin's power stroke in muscle contraction.

Main Methods:

3-D tomograms of insect flight muscle (IFM) fast-frozen during active contraction.
Fluorescence polarization and X-ray diffraction of isometrically contracting muscle fibers.
Atomic model rebuilding of nucleotide-free subfragment 1 (S1) based on experimental data.

Main Results:

Direct evidence for lever arm movements synchronous with force changes in muscle fibers.
A two-stage power stroke model for myosin: catalytic domain rolling followed by a 5-nm lever arm swing.
Actin binding appears necessary to observe the complete range of myosin motor action.

Conclusions:

The swinging crossbridge hypothesis is supported by direct experimental evidence.
Myosin's power stroke involves coordinated movements of the catalytic and lever arm domains.
Actin-myosin interactions and ATP hydrolysis contribute to crossbridge cocking and power stroke execution.

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