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 C0 and C1 N-terminal Ig domains of myosin binding protein C exert different effects on thin filament activation

2016 ◽  
Vol 113 (6) ◽  
pp. 1558-1563 ◽  
Author(s):  
Samantha P. Harris ◽  
Betty Belknap ◽  
Robert E. Van Sciver ◽  
Howard D. White ◽  
Vitold E. Galkin
Keyword(s):  
Protein C ◽  
Thin Filament ◽  
Molecular Motor ◽  
Binding Protein ◽  
Myosin Binding Protein ◽  
Myosin Binding Protein C ◽  
Genes Encoding ◽  
Myosin Subfragment 1 ◽  
Filament Activation ◽  
Myosin Binding

Mutations in genes encoding myosin, the molecular motor that powers cardiac muscle contraction, and its accessory protein, cardiac myosin binding protein C (cMyBP-C), are the two most common causes of hypertrophic cardiomyopathy (HCM). Recent studies established that the N-terminal domains (NTDs) of cMyBP-C (e.g., C0, C1, M, and C2) can bind to and activate or inhibit the thin filament (TF). However, the molecular mechanism(s) by which NTDs modulate interaction of myosin with the TF remains unknown and the contribution of each individual NTD to TF activation/inhibition is unclear. Here we used an integrated structure–function approach using cryoelectron microscopy, biochemical kinetics, and force measurements to reveal how the first two Ig-like domains of cMyPB-C (C0 and C1) interact with the TF. Results demonstrate that despite being structural homologs, C0 and C1 exhibit different patterns of binding on the surface of F-actin. Importantly, C1 but not C0 binds in a position to activate the TF by shifting tropomyosin (Tm) to the “open” structural state. We further show that C1 directly interacts with Tm and traps Tm in the open position on the surface of F-actin. Both C0 and C1 compete with myosin subfragment 1 for binding to F-actin and effectively inhibit actomyosin interactions when present at high ratios of NTDs to F-actin. Finally, we show that in contracting sarcomeres, the activating effect of C1 is apparent only once low levels of Ca2+ have been achieved. We suggest that Ca2+ modulates the interaction of cMyBP-C with the TF in the sarcomere.

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.

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 Cardiac Myosin Binding Protein-C Is Essential for Thick-Filament Stability and Flexural Rigidity

2009 ◽  
Vol 96 (8) ◽  
pp. 3273-3280 ◽  
Author(s):  
Lori R. Nyland ◽  
Bradley M. Palmer ◽  
Zengyi Chen ◽  
David W. Maughan ◽  
Christine E. Seidman ◽  
...  
Keyword(s):  
Protein C ◽  
Flexural Rigidity ◽  
Binding Protein ◽  
Thick Filament ◽  
Cardiac Myosin ◽  
Myosin Binding Protein ◽  
Myosin Binding Protein C ◽  
Myosin Binding
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