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Nature. 2015 Dec 10;528(7581):276-9. doi: 10.1038/nature15727. Epub 2015 Nov 11.

Force generation by skeletal muscle is controlled by mechanosensing in myosin filaments.

Author information

1
Laboratory of Physiology, Department of Biology, Università di Firenze, Sesto Fiorentino, 50019 Florence, Italy.
2
Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, UdR Firenze, Sesto Fiorentino, 50019 Florence, Italy.
3
Randall Division and BHF Centre for Research Excellence, King's College London, London SE1 1UL, UK.
4
European Synchrotron Radiation Facility, BP220, F-38043 Grenoble, France.

Abstract

Contraction of both skeletal muscle and the heart is thought to be controlled by a calcium-dependent structural change in the actin-containing thin filaments, which permits the binding of myosin motors from the neighbouring thick filaments to drive filament sliding. Here we show by synchrotron small-angle X-ray diffraction of frog (Rana temporaria) single skeletal muscle cells that, although the well-known thin-filament mechanism is sufficient for regulation of muscle shortening against low load, force generation against high load requires a second permissive step linked to a change in the structure of the thick filament. The resting (switched 'OFF') structure of the thick filament is characterized by helical tracks of myosin motors on the filament surface and a short backbone periodicity. This OFF structure is almost completely preserved during low-load shortening, which is driven by a small fraction of constitutively active (switched 'ON') myosin motors outside thick-filament control. At higher load, these motors generate sufficient thick-filament stress to trigger the transition to its long-periodicity ON structure, unlocking the major population of motors required for high-load contraction. This concept of the thick filament as a regulatory mechanosensor provides a novel explanation for the dynamic and energetic properties of skeletal muscle. A similar mechanism probably operates in the heart.

PMID:
26560032
DOI:
10.1038/nature15727
[Indexed for MEDLINE]

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