Positioning of Myosin-Binding Protein C in Skeletal Muscle

Fast skeletal myosin-binding protein-C (fMyBP-C) is one of three MyBP-C paralogs and is predominantly expressed in fast skeletal muscle. Mutations in the gene that encodes fMyBP-C, MYBPC2, are associated with distal arthrogryposis, while loss of fMyBP-C protein is associated with diseased muscle. However, the functional and structural roles of fMyBP-C in skeletal muscle remain unclear. To address this gap, we generated a homozygous fMyBP-C knockout mouse (C2−/−) and characterized it both in vivo and in vitro compared to wild-type mice. Ablation of fMyBP-C was benign in terms of muscle weight, fiber type, cross-sectional area, and sarcomere ultrastructure. However, grip strength and plantar flexor muscle strength were significantly decreased in C2−/− mice. Peak isometric tetanic force and isotonic speed of contraction were significantly reduced in isolated extensor digitorum longus (EDL) from C2−/− mice. Small-angle X-ray diffraction of C2−/− EDL muscle showed significantly increased equatorial intensity ratio during contraction, indicating a greater shift of myosin heads toward actin, while MLL4 layer line intensity was decreased at rest, indicating less ordered myosin heads. Interfilament lattice spacing increased significantly in C2−/− EDL muscle. Consistent with these findings, we observed a significant reduction of steady-state isometric force during Ca2+-activation, decreased myofilament calcium sensitivity, and sinusoidal stiffness in skinned EDL muscle fibers from C2−/− mice. Finally, C2−/− muscles displayed disruption of inflammatory and regenerative pathways, along with increased muscle damage upon mechanical overload. Together, our data suggest that fMyBP-C is essential for maximal speed and force of contraction, sarcomere integrity, and calcium sensitivity in fast-twitch muscle.

Download Full-text

What a drag!: Skeletal myosin binding protein-C affects sarcomeric shortening

The Journal of General Physiology ◽

10.1085/jgp.201912326 ◽

2019 ◽

Vol 151 (5) ◽

pp. 614-618

Author(s):

Brett A. Colson

Keyword(s):

Skeletal Muscle ◽

Protein C ◽

Binding Protein ◽

Functional Effect ◽

Slow Myosin ◽

Myosin Binding Protein ◽

Myosin Binding Protein C ◽

Skeletal Myosin ◽

Myosin Binding ◽

Slow Twitch

Colson discusses a recent investigation of the functional effect of slow myosin binding protein-C in slow-twitch skeletal muscle fibers.

Download Full-text

ID: 77: FAST-SKELETAL MYOSIN BINDING PROTEIN-C REGULATES SKELETAL MUSCLE CALCIUM SENSITIVITY

Journal of Investigative Medicine ◽

10.1136/jim-2016-000120.13 ◽

2016 ◽

Vol 64 (4) ◽

pp. 917.1-917

Author(s):

BL Lin ◽

S Govindan ◽

S Sadayappan ◽

L Zhao ◽

J Xu ◽

...

Keyword(s):

Skeletal Muscle ◽

Muscle Contraction ◽

Skeletal Muscles ◽

Protein C ◽

Molecular Level ◽

Binding Protein ◽

Myosin Binding Protein ◽

Myosin Binding Protein C ◽

Myosin Binding

Mutations in myosin binding protein-C (MyBP-C) cause both cardiac and skeletal muscle diseases, such as hypertrophic cardiomyopathy and distal arthrogryposis. There are three isoforms of MyBP-C: slow-skeletal, fast-skeletal, and cardiac (ssMyBP-C, fsMyBP-C, and cMyBP-C, respectively). These isoforms reside within the sarcomere, the functional unit of muscle contraction at the molecular level. However, the function of the three major MyBP-C isoforms remains unclear. The present study is the first to focus on the least characterized isoform, fsMyBP-C, which is expressed in fast- and mixed-type skeletal muscles. To determine the necessity of fsMyBP-C for regulation of contraction in the sarcomere, we generated a conventional fast-skeletal MyBP-C knockout (FSKO) mouse model. We analyzed both structural changes and regulatory function of skeletal muscles from heterozygous (FSKO−/+) and homozygous (FSKO−/−), compared to wild-type (WT) mice. Neither heterozygous nor homozygous FSKO mice exhibited changes in morbidity or mortality relative to WT mice. Molecular analyses revealed a complete knockout of fsMyBP-C in the FSKO−/− skeletal muscles compared to FSKO−/+ and WT mice. Histopathological analyses of both Extensor digitorum longus (EDL) and soleus muscles revealed no obvious abnormalities, such as fibrosis or calcification, in either heterozygous or homozygous FSKO mice. Though fiber structure is preserved, we demonstrated that EDL muscles from FSKO−/− mice increases Ca2+-sensitivity of force development, suggesting that fsMyBP-C regulates contraction at the molecular level by decreasing Ca2+-sensitivity. While others have previously proposed the role of cMyBP-C is to increase Ca2+-sensitivity to normalize a Ca2+ gradient imbalance in the heart, we propose that the role of fsMyBP-C in skeletal muscles is to reduce Ca2+-sensitivity of the thin filaments in order to normalize the reversed Ca2+ gradient imbalance. Despite opposite effects on Ca2+-sensitivity, MyBP-C share the same functional role in both cardiac and skeletal muscles. Thus, in addition to elucidating the role of fast-skeletal MyBP-C and its regulation of skeletal muscle contraction, the present study provides insight into the cardiac isoform and its regulation of cardiac contraction.

Download Full-text

Imaging ATP Consumption in Resting Skeletal Muscle: One Molecule at a Time

10.1101/2020.05.27.119065 ◽

2020 ◽

Cited By ~ 3

Author(s):

Shane R. Nelson ◽

Amy Li ◽

Samantha Beck-Previs ◽

Guy G. Kennedy ◽

David M. Warshaw

Keyword(s):

Skeletal Muscle ◽

Single Molecule ◽

Protein C ◽

Contractile Function ◽

Binding Protein ◽

Hydrolysis Rate ◽

Skeletal Muscle Myosin ◽

Myosin Binding Protein ◽

Myosin Binding Protein C ◽

Myosin Binding

AbstractMuscle contraction is driven by sarcomere shortening and powered by cyclic hydrolysis of ATP by myosin molecular motors. However, myosin in relaxed muscle continues to slowly hydrolyze ATP, analogous to an idling engine. Utilizing super-resolution microscopy to directly image single molecule fluorescent ATP turnover in relaxed rat soleus skeletal muscle sarcomeres, we observed two rates of myosin ATP consumption that differed 5-fold. These distinct hydrolysis rates were spatially segregated, with the slower or “super relaxed” rate localized predominantly to the sarcomere C-zone, where Myosin Binding Protein-C (MyBP-C), a known modulator of muscle contractile function, exists. This super relaxed hydrolysis rate and its location suggest that MyBP-C can sequester myosin motors to regulate muscle metabolism and heat production in resting muscle and force generation upon activation.One Sentence SummarySuper relaxed skeletal muscle myosin is stabilized by Myosin-Binding Protein C as imaged by single ATP molecule consumption.

Download Full-text