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 sliding1, 2, 3. 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 periodicity2, 4, 5. 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.

Force generation by skeletal muscle is controlled by mechanosensing in myosin filaments / M. Linari; E. Brunello; M. Reconditi; L. Fusi; M. Caremani; T. Narayanan; G. Piazzesi; V. Lombardi; M. Irving.. - In: NATURE. - ISSN 0028-0836. - STAMPA. - 528:(2015), pp. 276-279. [10.1038/nature15727]

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

LINARI, MARCO;BRUNELLO, ELISABETTA;RECONDITI, MASSIMO;CAREMANI, MARCO;PIAZZESI, GABRIELLA;LOMBARDI, VINCENZO;
2015

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 sliding1, 2, 3. 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 periodicity2, 4, 5. 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.
2015
528
276
279
Goal 3: Good health and well-being for people
M. Linari; E. Brunello; M. Reconditi; L. Fusi; M. Caremani; T. Narayanan; G. Piazzesi; V. Lombardi; M. Irving.
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