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Title: Nebulin and titin modulate cross-bridge cycling and length-dependent calcium sensitivity

Journal Article · · Journal of General Physiology

Various mutations in the structural proteins nebulin and titin that are present in human disease are known to affect the contractility of striated muscle. Loss of nebulin is associated with reduced actin filament length and impairment of myosin binding to actin, whereas titin is thought to regulate muscle passive elasticity and is likely involved in length-dependent activation. Here, we sought to assess the modulation of muscle function by these sarcomeric proteins by using the computational platform muscle simulation code (MUSICO) to quantitatively separate the effects of structural changes, kinetics of cross-bridge cycling, and calcium sensitivity of the thin filaments. The simulations show that variation in thin filament length cannot by itself account for experimental observations of the contractility in nebulin-deficient muscle, but instead must be accompanied by a decreased myosin binding rate. Additionally, to match the observed calcium sensitivity, the rate of TnI detachment from actin needed to be increased. Simulations for cardiac muscle provided quantitative estimates of the effects of different titin-based passive elasticities on muscle force and activation in response to changes in sarcomere length and interfilament lattice spacing. Predicted force–pCa relations showed a decrease in both active tension and sensitivity to calcium with a decrease in passive tension and sarcomere length. We conclude that this behavior is caused by partial redistribution of the muscle load between active muscle force and titin-dependent passive force, and also by redistribution of stretch along the thin filament, which together modulate the release of TnI from actin. These data help advance understanding of how nebulin and titin mutations affect muscle function.

Research Organization:
Argonne National Laboratory (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Organization:
National Institutes of Health (NIH); British Heart Foundation; European Research Council (ERC); Serbian Ministry of Science
Grant/Contract Number:
R01 AR048776; P41 GM103622; R35HL144998; R01AR053897; III41007; OI174028; R01 DC 011528
OSTI ID:
1558308
Journal Information:
Journal of General Physiology, Vol. 151, Issue 5; ISSN 0022-1295
Publisher:
Rockefeller University PressCopyright Statement
Country of Publication:
United States
Language:
ENGLISH
Citation Metrics:
Cited by: 22 works
Citation information provided by
Web of Science

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Cited By (7)

Expressing a Z-disk nebulin fragment in nebulin-deficient mouse muscle: effects on muscle structure and function journal January 2020
Progress on the regulation of myofibrillar function: Part 2 journal April 2019
Calcium-dependent titin–thin filament interactions in muscle: observations and theory journal July 2019
The mechanism of thin filament regulation: Models in conflict? journal September 2019
Estimation of Forces on Actin Filaments in Living Muscle from X-ray Diffraction Patterns and Mechanical Data journal November 2019
Elastic domains of giant proteins in striated muscle: Modeling compliance with rulers journal April 2019
Nebulin: big protein with big responsibilities journal January 2020

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