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Activation of skeletal muscle is controlled by a dual-filament mechano-sensing mechanism

Contraction of skeletal muscle is triggered by a transient rise in intracellular calcium concentration leading to a structural change in the actin-containing thin filaments that allows binding of myosin motors from the thick filaments. Most myosin motors are unavailable for actin binding in resting...

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Autores principales: Brunello, Elisabetta, Marcucci, Lorenzo, Irving, Malcolm, Fusi, Luca
Formato: Online Artículo Texto
Lenguaje:English
Publicado: National Academy of Sciences 2023
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10235942/
https://www.ncbi.nlm.nih.gov/pubmed/37216507
http://dx.doi.org/10.1073/pnas.2302837120
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author Brunello, Elisabetta
Marcucci, Lorenzo
Irving, Malcolm
Fusi, Luca
author_facet Brunello, Elisabetta
Marcucci, Lorenzo
Irving, Malcolm
Fusi, Luca
author_sort Brunello, Elisabetta
collection PubMed
description Contraction of skeletal muscle is triggered by a transient rise in intracellular calcium concentration leading to a structural change in the actin-containing thin filaments that allows binding of myosin motors from the thick filaments. Most myosin motors are unavailable for actin binding in resting muscle because they are folded back against the thick filament backbone. Release of the folded motors is triggered by thick filament stress, implying a positive feedback loop in the thick filaments. However, it was unclear how thin and thick filament activation mechanisms are coordinated, partly because most previous studies of the thin filament regulation were conducted at low temperatures where the thick filament mechanisms are inhibited. Here, we use probes on both troponin in the thin filaments and myosin in the thick filaments to monitor the activation states of both filaments in near-physiological conditions. We characterize those activation states both in the steady state, using conventional titrations with calcium buffers, and during activation on the physiological timescale, using calcium jumps produced by photolysis of caged calcium. The results reveal three activation states of the thin filament in the intact filament lattice of a muscle cell that are analogous to those proposed previously from studies on isolated proteins. We characterize the rates of the transitions between these states in relation to thick filament mechano-sensing and show how thin- and thick-filament-based mechanisms are coupled by two positive feedback loops that switch on both filaments to achieve rapid cooperative activation of skeletal muscle.
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spelling pubmed-102359422023-06-03 Activation of skeletal muscle is controlled by a dual-filament mechano-sensing mechanism Brunello, Elisabetta Marcucci, Lorenzo Irving, Malcolm Fusi, Luca Proc Natl Acad Sci U S A Biological Sciences Contraction of skeletal muscle is triggered by a transient rise in intracellular calcium concentration leading to a structural change in the actin-containing thin filaments that allows binding of myosin motors from the thick filaments. Most myosin motors are unavailable for actin binding in resting muscle because they are folded back against the thick filament backbone. Release of the folded motors is triggered by thick filament stress, implying a positive feedback loop in the thick filaments. However, it was unclear how thin and thick filament activation mechanisms are coordinated, partly because most previous studies of the thin filament regulation were conducted at low temperatures where the thick filament mechanisms are inhibited. Here, we use probes on both troponin in the thin filaments and myosin in the thick filaments to monitor the activation states of both filaments in near-physiological conditions. We characterize those activation states both in the steady state, using conventional titrations with calcium buffers, and during activation on the physiological timescale, using calcium jumps produced by photolysis of caged calcium. The results reveal three activation states of the thin filament in the intact filament lattice of a muscle cell that are analogous to those proposed previously from studies on isolated proteins. We characterize the rates of the transitions between these states in relation to thick filament mechano-sensing and show how thin- and thick-filament-based mechanisms are coupled by two positive feedback loops that switch on both filaments to achieve rapid cooperative activation of skeletal muscle. National Academy of Sciences 2023-05-22 2023-05-30 /pmc/articles/PMC10235942/ /pubmed/37216507 http://dx.doi.org/10.1073/pnas.2302837120 Text en Copyright © 2023 the Author(s). Published by PNAS. https://creativecommons.org/licenses/by/4.0/This open access article is distributed under Creative Commons Attribution License 4.0 (CC BY) (https://creativecommons.org/licenses/by/4.0/) .
spellingShingle Biological Sciences
Brunello, Elisabetta
Marcucci, Lorenzo
Irving, Malcolm
Fusi, Luca
Activation of skeletal muscle is controlled by a dual-filament mechano-sensing mechanism
title Activation of skeletal muscle is controlled by a dual-filament mechano-sensing mechanism
title_full Activation of skeletal muscle is controlled by a dual-filament mechano-sensing mechanism
title_fullStr Activation of skeletal muscle is controlled by a dual-filament mechano-sensing mechanism
title_full_unstemmed Activation of skeletal muscle is controlled by a dual-filament mechano-sensing mechanism
title_short Activation of skeletal muscle is controlled by a dual-filament mechano-sensing mechanism
title_sort activation of skeletal muscle is controlled by a dual-filament mechano-sensing mechanism
topic Biological Sciences
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10235942/
https://www.ncbi.nlm.nih.gov/pubmed/37216507
http://dx.doi.org/10.1073/pnas.2302837120
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