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Nebulin stiffens the thin filament and augments cross-bridge interaction in skeletal muscle

Journal Article · · Proceedings of the National Academy of Sciences of the United States of America
 [1];  [1];  [2];  [1];  [1];  [2];  [2];  [1]
  1. Univ. of Arizona, Tucson, AZ (United States)
  2. Illinois Inst. of Technology, Chicago, IL (United States)
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Nebulin is a giant sarcomeric protein that spans along the actin filament in skeletal muscle, from the Z-disk to near the thin filament pointed end. Mutations in nebulin cause muscle weakness in nemaline myopathy patients, suggesting that nebulin plays important roles in force generation, yet little is known about nebulin’s influence on thin filament structure and function. Here, we used small-angle X-ray diffraction and compared intact muscle deficient in nebulin (using a conditional nebulin-knockout, Neb cKO) with control (Ctrl) muscle. When muscles were activated, the spacing of the actin subunit repeat (27 Å) increased in both genotypes; when converted to thin filament stiffness, the obtained value was 30 pN/nm in Ctrl muscle and 10 pN/nm in Neb cKO muscle; that is, the thin filament was approximately threefold stiffer when nebulin was present. In contrast, the thick filament stiffness was not different between the genotypes. A significantly shorter left-handed (59 Å) thin filament helical pitch was found in passive and contracting Neb cKO muscles, as well as impaired tropomyosin and troponin movement. Additionally, a reduced myosin mass transfer toward the thin filament in contracting Neb cKO muscle was found, suggesting reduced cross-bridge interaction. Here, we conclude that nebulin is critically important for physiological force levels, as it greatly stiffens the skeletal muscle thin filament and contributes to thin filament activation and cross-bridge recruitment.

Research Organization:
Argonne National Laboratory (ANL), Argonne, IL (United States)
Sponsoring Organization:
USDOE; NIH; National Inst. of General Medical Sciences (NIGMS)
Grant/Contract Number:
AC02-06CH11357
OSTI ID:
1478092
Journal Information:
Proceedings of the National Academy of Sciences of the United States of America, Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Issue: 41 Vol. 115; ISSN 0027-8424
Publisher:
National Academy of SciencesCopyright Statement
Country of Publication:
United States
Language:
ENGLISH

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Cited By (9)

Nebulin and titin modulate cross-bridge cycling and length-dependent calcium sensitivity journal April 2019
Elastic domains of giant proteins in striated muscle: Modeling compliance with rulers journal April 2019
Omecamtiv mecarbil lowers the contractile deficit in a mouse model of nebulin-based nemaline myopathy journal November 2019
Functional Characterization of the Intact Diaphragm in a Nebulin-Based Nemaline Myopathy (NM) Model-Effects of the Fast Skeletal Muscle Troponin Activator tirasemtiv journal October 2019
Estimation of Forces on Actin Filaments in Living Muscle from X-ray Diffraction Patterns and Mechanical Data journal November 2019
Nebulin: big protein with big responsibilities journal January 2020
Nebulin no longer nebulous journal October 2018
KBTBD13 is an actin-binding protein that modulates muscle kinetics journal December 2019
Nebulin nemaline myopathy recapitulated in a compound heterozygous mouse model with both a missense and a nonsense mutation in Neb journal February 2020

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Related Subjects

59 BASIC BIOLOGICAL SCIENCES
X-ray diffraction
muscle biology
physiology
skeletal myopathy