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

TY - JOUR

T1 - Force generation by skeletal muscle is controlled by mechanosensing in myosin filaments

AU - Linari, Marco

AU - Brunello, Elisabetta

AU - Reconditi, Massimo

AU - Fusi, Luca

AU - Caremani, Marco

AU - Narayanan, Theyencheri

AU - Piazzesi, Gabriella

AU - Lombardi, Vincenzo

AU - Irving, Malcolm

PY - 2015/12/10

Y1 - 2015/12/10

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=84949779756&partnerID=8YFLogxK

U2 - 10.1038/nature15727

DO - 10.1038/nature15727

M3 - Article

AN - SCOPUS:84949779756

SN - 0028-0836

VL - 528

SP - 276

EP - 279

JO - NATURE

JF - NATURE

IS - 7581

ER -