scholarly journals SKELETAL MyBP-C ISOFORMS TUNE THE MOLECULAR CONTRACTILITY OF DIVERGENT SKELETAL MUSCLE SYSTEMS

2019 ◽  
Author(s):  
Amy Li ◽  
Shane Nelson ◽  
Sheema Rahmanseresht ◽  
Filip Braet ◽  
Anabelle S. Cornachione ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Thin Filament ◽  
Thick Filament ◽  
Muscle Contractility ◽  
Myosin Binding Protein ◽  
Myosin Binding Protein C ◽  
N Terminus ◽  
Slow Type ◽  
Myosin Binding ◽  
Slow Twitch

ABSTRACTSkeletal muscle myosin-binding protein C (MyBP-C) is a myosin thick filament-associated protein; localized through its C terminus to distinct regions (C-zones) of the sarcomere. MyBP-C modulates muscle contractility, presumably through its N terminus extending from the thick filament and interacting with either the myosin head region and/or the actin thin filament. Two isoforms of MyBP-C (fast- and slow-type) are expressed in a muscle-type specific manner. Are the expression, localization, and Ca2+-dependent modulatory capacities of these isoforms different in fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus (SOL) muscles derived from Sprague-Dawley rats? By mass spectrometry, four MyBP-C isoforms (one fast-type MyBP-C and three N-terminally spliced slow-type MyBP-C) were expressed in EDL but only the three slow-type MyBP-C isoforms in SOL. Using EDL and SOL native thick filaments in which the MyBP-C stoichiometry and localization are preserved, native thin filament sliding over these thick filaments showed that only in the C-zone, MyBP-C Ca2+-sensitizes the thin filament and slows thin filament velocity. These modulatory properties depended on MyBP-C’s N-terminus, as N-terminal proteolysis attenuated MyBP-C’s functional capacities. To determine each MyBP-C isoform’s contribution to thin filament Ca2+-sensitization and slowing in the C-zone, we used a combination of in vitro motility assays using expressed recombinant N-terminal fragments and in silico mechanistic modeling. Our results suggest that each skeletal MyBP-C isoform’s N terminus is functionally distinct and has modulatory capacities that depend on the muscle-type in which they are expressed, providing the potential for molecular tuning of skeletal muscle performance through differential MyBP-C expression.SIGNIFICANCEMyosin-binding protein C (MyBP-C) is a critical component of the skeletal muscle sarcomere, muscle’s smallest contractile unit. MyBP-C’s importance is evident by genetic mutations leading to human myopathies, such as distal arthrogryposis (i.e. club foot). However, the molecular basis of MyBP-C’s functional impact on skeletal muscle contractility is far from certain. Complicating matters further is the expression of fast- and slow-type MyBP-C isoforms that depend on whether the muscle is fast- or slow-twitch. Using multi-scale proteomic, biophysical and mathematical modeling approaches, we define the expression, localization, and modulatory capacities of these distinct skeletal MyBP-C isoforms in rat skeletal muscles. Each MyBP-C isoform appears to modulate muscle contractility differentially; providing the capacity to fine-tune muscle’s mechanical performance as physiological demands arise.

scholarly journals During muscle atrophy, thick, but not thin, filament components are degraded by MuRF1-dependent ubiquitylation

2009 ◽  
Vol 185 (6) ◽  
pp. 1083-1095 ◽  
Author(s):  
Shenhav Cohen ◽  
Jeffrey J. Brault ◽  
Steven P. Gygi ◽  
David J. Glass ◽  
David M. Valenzuela ◽  
...  
Keyword(s):  
Ubiquitin Ligase ◽  
Protein C ◽  
Thin Filament ◽  
Muscle Wasting ◽  
Ring Finger ◽  
Thick Filament ◽  
Myosin Binding Protein ◽  
Myosin Binding Protein C ◽  
Associated Proteins ◽  
Myosin Binding

Loss of myofibrillar proteins is a hallmark of atrophying muscle. Expression of muscle RING-finger 1 (MuRF1), a ubiquitin ligase, is markedly induced during atrophy, and MuRF1 deletion attenuates muscle wasting. We generated mice expressing a Ring-deletion mutant MuRF1, which binds but cannot ubiquitylate substrates. Mass spectrometry of the bound proteins in denervated muscle identified many myofibrillar components. Upon denervation or fasting, atrophying muscles show a loss of myosin-binding protein C (MyBP-C) and myosin light chains 1 and 2 (MyLC1 and MyLC2) from the myofibril, before any measurable decrease in myosin heavy chain (MyHC). Their selective loss requires MuRF1. MyHC is protected from ubiquitylation in myofibrils by associated proteins, but eventually undergoes MuRF1-dependent degradation. In contrast, MuRF1 ubiquitylates MyBP-C, MyLC1, and MyLC2, even in myofibrils. Because these proteins stabilize the thick filament, their selective ubiquitylation may facilitate thick filament disassembly. However, the thin filament components decreased by a mechanism not requiring MuRF1.

scholarly journals Inotropic interventions do not change the resting state of myosin motors during cardiac diastole

2018 ◽  
Vol 151 (1) ◽  
pp. 53-65 ◽  
Author(s):  
Marco Caremani ◽  
Francesca Pinzauti ◽  
Joseph D. Powers ◽  
Serena Governali ◽  
Theyencheri Narayanan ◽  
...  
Keyword(s):  
Protein C ◽  
Thin Filament ◽  
Sarcomere Length ◽  
Binding Protein ◽  
Thick Filament ◽  
Myosin Binding Protein ◽  
Myosin Binding Protein C ◽  
Filament Activation ◽  
Myosin Binding ◽  
Myosin Motors

When striated (skeletal and cardiac) muscle is in its relaxed state, myosin motors are packed in helical tracks on the surface of the thick filament, folded toward the center of the sarcomere, and unable to bind actin or hydrolyze ATP (OFF state). This raises the question of whatthe mechanism is that integrates the Ca2+-dependent thin filament activation, making myosin heads available for interaction with actin. Here we test the interdependency of the thin and thick filament regulatory mechanisms in intact trabeculae from the rat heart. We record the x-ray diffraction signals that mark the state of the thick filament during inotropic interventions (increase in sarcomere length from 1.95 to 2.25 µm and addition of 10−7 M isoprenaline), which potentiate the twitch force developed by an electrically paced trabecula by up to twofold. During diastole, none of the signals related to the OFF state of the thick filament are significantly affected by these interventions, except the intensity of both myosin-binding protein C– and troponin-related meridional reflections, which reduce by 20% in the presence of isoprenaline. These results indicate that recruitment of myosin motors from their OFF state occurs independently and downstream from thin filament activation. This is in agreement with the recently discovered mechanism based on thick filament mechanosensing in which the number of motors available for interaction with actin rapidly adapts to the stress on the thick filament and thus to the loading conditions of the contraction. The gain of this positive feedback may be modulated by both sarcomere length and the degree of phosphorylation of myosin-binding protein C.

scholarly journals Regulation of myofilament force and loaded shortening by skeletal myosin binding protein C

2019 ◽  
Vol 151 (5) ◽  
pp. 645-659 ◽  
Author(s):  
Joel C. Robinett ◽  
Laurin M. Hanft ◽  
Janelle Geist ◽  
Aikaterini Kontrogianni-Konstantopoulos ◽  
Kerry S. McDonald
Keyword(s):  
Skeletal Muscle ◽  
Protein C ◽  
Sarcomere Length ◽  
Force Development ◽  
Myosin Binding Protein ◽  
Myosin Binding Protein C ◽  
Myosin Binding ◽  
Slow Twitch ◽  
Fast Twitch ◽  
Transient Force

Myosin binding protein C (MyBP-C) is a 125–140-kD protein located in the C-zone of each half-thick filament. It is thought to be an important regulator of contraction, but its precise role is unclear. Here we investigate mechanisms by which skeletal MyBP-C regulates myofilament function using rat permeabilized skeletal muscle fibers. We mount either slow-twitch or fast-twitch skeletal muscle fibers between a force transducer and motor, use Ca2+ to activate a range of forces, and measure contractile properties including transient force overshoot, rate of force development, and loaded sarcomere shortening. The transient force overshoot is greater in slow-twitch than fast-twitch fibers at all Ca2+ activation levels. In slow-twitch fibers, protein kinase A (PKA) treatment (a) augments phosphorylation of slow skeletal MyBP-C (sMyBP-C), (b) doubles the magnitude of the relative transient force overshoot at low Ca2+ activation levels, and (c) increases force development rates at all Ca2+ activation levels. We also investigate the role that phosphorylated and dephosphorylated sMyBP-C plays in loaded sarcomere shortening. We test the hypothesis that MyBP-C acts as a brake to filament sliding within the myofilament lattice by measuring sarcomere shortening as thin filaments traverse into the C-zone during lightly loaded slow-twitch fiber contractions. Before PKA treatment, shortening velocity decelerates as sarcomeres traverse from ∼3.10 to ∼3.00 µm. After PKA treatment, sarcomeres shorten a greater distance and exhibit less deceleration during similar force clamps. After sMyBP-C dephosphorylation, sarcomere length traces display a brief recoil (i.e., “bump”) that initiates at ∼3.06 µm during loaded shortening. Interestingly, the timing of the bump shifts with changes in load but manifests at the same sarcomere length. Our results suggest that sMyBP-C and its phosphorylation state regulate sarcomere contraction by a combination of cross-bridge recruitment, modification of cross-bridge cycling kinetics, and alteration of drag forces that originate in the C-zone.

scholarly journals Skeletal MyBP-C isoforms tune the molecular contractility of divergent skeletal muscle systems

2019 ◽  
Vol 116 (43) ◽  
pp. 21882-21892 ◽  
Author(s):  
Amy Li ◽  
Shane R. Nelson ◽  
Sheema Rahmanseresht ◽  
Filip Braet ◽  
Anabelle S. Cornachione ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Thin Filament ◽  
Thick Filament ◽  
Mechanistic Modeling ◽  
Muscle Performance ◽  
Muscle Type ◽  
Skeletal Muscle Myosin ◽  
Thick Filaments ◽  
N Terminus ◽  
Slow Type

Skeletal muscle myosin-binding protein C (MyBP-C) is a myosin thick filament-associated protein, localized through its C terminus to distinct regions (C-zones) of the sarcomere. MyBP-C modulates muscle contractility, presumably through its N terminus extending from the thick filament and interacting with either the myosin head region and/or the actin thin filament. Two isoforms of MyBP-C (fast- and slow-type) are expressed in a muscle type-specific manner. Are the expression, localization, and Ca2+-dependent modulatory capacities of these isoforms different in fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus (SOL) muscles derived from Sprague–Dawley rats? By mass spectrometry, 4 MyBP-C isoforms (1 fast-type MyBP-C and 3 N-terminally spliced slow-type MyBP-C) were expressed in EDL, but only the 3 slow-type MyBP-C isoforms in SOL. Using EDL and SOL native thick filaments in which the MyBP-C stoichiometry and localization are preserved, native thin filament sliding over these thick filaments showed that, only in the C-zone, MyBP-C Ca2+ sensitizes the thin filament and slows thin filament velocity. These modulatory properties depended on MyBP-C’s N terminus as N-terminal proteolysis attenuated MyBP-C’s functional capacities. To determine each MyBP-C isoform’s contribution to thin filament Ca2+ sensitization and slowing in the C-zone, we used a combination of in vitro motility assays using expressed recombinant N-terminal fragments and in silico mechanistic modeling. Our results suggest that each skeletal MyBP-C isoform’s N terminus is functionally distinct and has modulatory capacities that depend on the muscle type in which they are expressed, providing the potential for molecular tuning of skeletal muscle performance through differential MyBP-C expression.

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

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.

scholarly journals ADP-stimulated contraction: A predictor of thin-filament activation in cardiac disease

2015 ◽  
Vol 112 (50) ◽  
pp. E7003-E7012 ◽  
Author(s):  
Vasco Sequeira ◽  
Aref Najafi ◽  
Paul J. M. Wijnker ◽  
Cristobal G. dos Remedios ◽  
Michelle Michels ◽  
...  
Keyword(s):  
Thin Filament ◽  
Thick Filament ◽  
Actin Binding ◽  
Mutant Proteins ◽  
Force Development ◽  
Myosin Binding Protein ◽  
Myosin Binding Protein C ◽  
Filament Activation ◽  
Myosin Binding ◽  
Highly Correlated

Diastolic dysfunction is general to all idiopathic dilated (IDCM) and hypertrophic cardiomyopathy (HCM) patients. Relaxation deficits may result from increased actin–myosin formation during diastole due to altered tropomyosin position, which blocks myosin binding to actin in the absence of Ca2+. We investigated whether ADP-stimulated force development (without Ca2+) can be used to reveal changes in actin–myosin blockade in human cardiomyopathy cardiomyocytes. Cardiac samples from HCM patients, harboring thick-filament (MYH7mut, MYBPC3mut) and thin-filament (TNNT2mut, TNNI3mut) mutations, and IDCM were compared with sarcomere mutation-negative HCM (HCMsmn) and nonfailing donors. Myofilament ADP sensitivity was higher in IDCM and HCM compared with donors, whereas it was lower for MYBPC3. Increased ADP sensitivity in IDCM, HCMsmn, and MYH7mut was caused by low phosphorylation of myofilament proteins, as it was normalized to donors by protein kinase A (PKA) treatment. Troponin exchange experiments in a TNNT2mut sample corrected the abnormal actin–myosin blockade. In MYBPC3trunc samples, ADP sensitivity highly correlated with cardiac myosin-binding protein-C (cMyBP-C) protein level. Incubation of cardiomyocytes with cMyBP-C antibody against the actin-binding N-terminal region reduced ADP sensitivity, indicative of cMyBP-C’s role in actin–myosin regulation. In the presence of Ca2+, ADP increased myofilament force development and sarcomere stiffness. Enhanced sarcomere stiffness in sarcomere mutation-positive HCM samples was irrespective of the phosphorylation background. In conclusion, ADP-stimulated contraction can be used as a tool to study how protein phosphorylation and mutant proteins alter accessibility of myosin binding on actin. In the presence of Ca2+, pathologic [ADP] and low PKA-phosphorylation, high actin–myosin formation could contribute to the impaired myocardial relaxation observed in cardiomyopathies.

scholarly journals Skeletal Myosin-Binding Protein C Isoforms Differentially Regulate Fast- and Slow-Twitch Skeletal Muscle Function

2020 ◽  
Vol 118 (3) ◽  
pp. 278a
Author(s):  
Shane R. Nelson ◽  
Amy Li ◽  
Sheema Rahmanseresht ◽  
Filip Braet ◽  
Anabelle S. Cornachione ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Muscle Function ◽  
Protein C ◽  
Binding Protein ◽  
Skeletal Muscle Function ◽  
Myosin Binding Protein ◽  
Myosin Binding Protein C ◽  
Skeletal Myosin ◽  
Myosin Binding ◽  
Slow Twitch

scholarly journals Skeletal myosin binding protein-C isoforms regulate thin filament activity in a Ca2+-dependent manner

2018 ◽  
Vol 8 (1) ◽  
Author(s):  
Brian Leei Lin ◽  
Amy Li ◽  
Ji Young Mun ◽  
Michael J. Previs ◽  
Samantha Beck Previs ◽  
...  
Keyword(s):  
Protein C ◽  
Thin Filament ◽  
Binding Protein ◽  
Dependent Manner ◽  
Myosin Binding Protein ◽  
Myosin Binding Protein C ◽  
Skeletal Myosin ◽  
Myosin Binding

The carboxyl terminus of myosin binding protein C (MyBP-C, C-protein) specifies incorporation into the A-band of striated muscle

1996 ◽  
Vol 109 (1) ◽  
pp. 101-111 ◽  
Author(s):  
R. Gilbert ◽  
M.G. Kelly ◽  
T. Mikawa ◽  
D.A. Fischman
Keyword(s):  
Amino Acids ◽  
Protein C ◽  
Binding Protein ◽  
Thick Filament ◽  
Binding Domain ◽  
C Protein ◽  
Amino Terminal ◽  
Myosin Binding Protein ◽  
Myosin Binding Protein C ◽  
Myosin Binding

Myosin binding protein-C (MyBP-C), also known as C-protein, is a major constituent of the thick filaments of vertebrate striated muscles. The protein, approximately 130 kDa, consists of a series of 10 globular motifs (numbered I to X) each of approximately 90–100 amino acids, bearing resemblance to the C2-set of immunoglobins (Ig C2) and to the fibronectin type III (FnIII) motifs. Using pure preparations of myosin and MyBP-C, it has been demonstrated that the major myosin binding domain of MyBP-C resides within the C-terminal Ig C2 motif (motif X). However, in the context of the in vivo thick filament, it is uncertain if the latter domain is sufficient to target MyBP-C correctly to the A-band or if other regions of the molecule are required for this process. To answer this question, cultures of skeletal muscle myoblasts were transfected with expression plasmids encoding seven truncation mutants of MyBP-C, and their targeting to the A-band investigated by immunofluorescence microscopy. To distinguish the recombinant proteins from endogenous MyBP-C, a myc epitope was inserted at each amino terminus. Recombinant MyBP-C exhibited an identical distribution in the sarcomere to that of native MyBP-C; i.e. it was found exclusively in the C-zone of the A-band. A mutant encoding the C-terminal 372 amino acids, but lacking motifs I-VI (termed delta 1–6), also targeted correctly to the A-band. This fragment, which is composed of two Ig C2 and two FnIII motifs, was the minimal protein fragment required for correct A-band incorporation. Larger amino-terminal deletions or deletion of motif X, the myosin binding domain, abolished all localization to the A-band. One construct (delta 10) lacking only motif X strongly inhibited myofibril assembly. We conclude that the myosin binding domain of MyBP-C, although essential, is not sufficient for correct incorporation into the A-band and that motifs VII to IX are required for this process. The data suggest a topological model in which MyBP-C is associated with the thick filament through its C terminus.

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