1
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Thomasen FE, Skaalum T, Kumar A, Srinivasan S, Vanni S, Lindorff-Larsen K. Rescaling protein-protein interactions improves Martini 3 for flexible proteins in solution. Nat Commun 2024; 15:6645. [PMID: 39103332 DOI: 10.1038/s41467-024-50647-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2023] [Accepted: 07/15/2024] [Indexed: 08/07/2024] Open
Abstract
Multidomain proteins with flexible linkers and disordered regions play important roles in many cellular processes, but characterizing their conformational ensembles is difficult. We have previously shown that the coarse-grained model, Martini 3, produces too compact ensembles in solution, that may in part be remedied by strengthening protein-water interactions. Here, we show that decreasing the strength of protein-protein interactions leads to improved agreement with experimental data on a wide set of systems. We show that the 'symmetry' between rescaling protein-water and protein-protein interactions breaks down when studying interactions with or within membranes; rescaling protein-protein interactions better preserves the binding specificity of proteins with lipid membranes, whereas rescaling protein-water interactions preserves oligomerization of transmembrane helices. We conclude that decreasing the strength of protein-protein interactions improves the accuracy of Martini 3 for IDPs and multidomain proteins, both in solution and in the presence of a lipid membrane.
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Affiliation(s)
- F Emil Thomasen
- Linderstrøm-Lang Centre for Protein Science, Department of Biology, University of Copenhagen, DK-2200, Copenhagen N, Denmark.
| | - Tórur Skaalum
- Linderstrøm-Lang Centre for Protein Science, Department of Biology, University of Copenhagen, DK-2200, Copenhagen N, Denmark
| | - Ashutosh Kumar
- Department of Biology, University of Fribourg, Fribourg, Switzerland
- Swiss National Center for Competence in Research (NCCR) Bio-inspired Materials, University of Fribourg, Chemin des Verdiers 4, CH-1700, Fribourg, Switzerland
| | | | - Stefano Vanni
- Department of Biology, University of Fribourg, Fribourg, Switzerland.
- Swiss National Center for Competence in Research (NCCR) Bio-inspired Materials, University of Fribourg, Chemin des Verdiers 4, CH-1700, Fribourg, Switzerland.
| | - Kresten Lindorff-Larsen
- Linderstrøm-Lang Centre for Protein Science, Department of Biology, University of Copenhagen, DK-2200, Copenhagen N, Denmark.
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2
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Mertens J, De Lange WJ, Farrell ET, Harbaugh EC, Gauchan A, Fitzsimons DP, Moss RL, Ralphe JC. The W792R HCM missense mutation in the C6 domain of cardiac myosin binding protein-C increases contractility in neonatal mouse myocardium. J Mol Cell Cardiol 2024:S0022-2828(24)00123-8. [PMID: 39059462 DOI: 10.1016/j.yjmcc.2024.07.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/02/2024] [Revised: 07/22/2024] [Accepted: 07/23/2024] [Indexed: 07/28/2024]
Abstract
Missense mutations in cardiac myosin binding protein C (cMyBP-C) are known to cause hypertrophic cardiomyopathy (HCM). The W792R mutation in the C6 domain of cMyBP-C causes severe, early onset HCM in humans, yet its impact on the function of cMyBP-C and the mechanism through which it causes disease remain unknown. To fully characterize the effect of the W792R mutation on cardiac morphology and function in vivo, we generated a murine knock-in model. We crossed heterozygous W792RWR mice to produce homozygous mutant W792RRR, heterozygous W792RWR, and control W792RWW mice. W792RRR mice present with cardiac hypertrophy, myofibrillar disarray and fibrosis by postnatal day 10 (PND10), and do not survive past PND21. Full-length cMyBP-C is present at similar levels in W792RWW, W792RWR and W792RRR mice and is properly incorporated into the sarcomere. Heterozygous W792RWR mice displayed normal heart morphology and contractility. Permeabilized myocardium from PND10 W792RRR mice showed increased Ca2+ sensitivity, accelerated cross-bridge cycling kinetics, decreased cooperativity in the activation of force, and increased expression of hypertrophy-related genes. In silico modeling suggests that the W792R mutation destabilizes the fold of the C6 domain and increases torsion in the C5-C7 region, possibly impacting regulatory interactions of cMyBP-C with myosin and actin. Based on the data presented here, we propose a model in which mutant W792R cMyBP-C preferentially forms Ca2+ sensitizing interactions with actin, rather than inhibitory interactions with myosin. The W792R-cMyBP-C mouse model provides mechanistic insights into the pathology of this mutation and may provide a mechanism by which other central domain missense mutations in cMyBP-C may alter contractility, leading to HCM.
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Affiliation(s)
- Jasmine Mertens
- Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, United States of America; UW Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, United States of America
| | - Willem J De Lange
- Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, United States of America; UW Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, United States of America
| | - Emily T Farrell
- Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, United States of America; UW Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, United States of America
| | - Ella C Harbaugh
- Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, United States of America; UW Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, United States of America
| | - Angeela Gauchan
- Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, United States of America; UW Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, United States of America
| | - Daniel P Fitzsimons
- UW Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, United States of America; Department of Cell and Regenerative Biology, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, United States of America
| | - Richard L Moss
- UW Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, United States of America; Department of Cell and Regenerative Biology, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, United States of America
| | - J Carter Ralphe
- Department of Pediatrics, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, United States of America; UW Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, United States of America.
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3
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Doh CY, Schmidt AV, Chinthalapudi K, Stelzer JE. Bringing into focus the central domains C3-C6 of myosin binding protein C. Front Physiol 2024; 15:1370539. [PMID: 38487262 PMCID: PMC10937550 DOI: 10.3389/fphys.2024.1370539] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2024] [Accepted: 02/19/2024] [Indexed: 03/17/2024] Open
Abstract
Myosin binding protein C (MyBPC) is a multi-domain protein with each region having a distinct functional role in muscle contraction. The central domains of MyBPC have often been overlooked due to their unclear roles. However, recent research shows promise in understanding their potential structural and regulatory functions. Understanding the central region of MyBPC is important because it may have specialized function that can be used as drug targets or for disease-specific therapies. In this review, we provide a brief overview of the evolution of our understanding of the central domains of MyBPC in regard to its domain structures, arrangement and dynamics, interaction partners, hypothesized functions, disease-causing mutations, and post-translational modifications. We highlight key research studies that have helped advance our understanding of the central region. Lastly, we discuss gaps in our current understanding and potential avenues to further research and discovery.
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Affiliation(s)
- Chang Yoon Doh
- Department of Medicine, School of Medicine, Case Western Reserve University, Cleveland, OH, United States
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH, United States
| | - Alexandra V. Schmidt
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH, United States
| | - Krishna Chinthalapudi
- Department of Physiology and Cell Biology, Dorothy M. Davis Heart & Lung Research Institute, College of Medicine, The Ohio State University, Columbus, OH, United States
| | - Julian E. Stelzer
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH, United States
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4
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Pearce A, Ponnam S, Holt MR, Randall T, Beckingham R, Kho AL, Kampourakis T, Ehler E. Missense mutations in the central domains of cardiac myosin binding protein-C and their potential contribution to hypertrophic cardiomyopathy. J Biol Chem 2024; 300:105511. [PMID: 38042491 PMCID: PMC10772716 DOI: 10.1016/j.jbc.2023.105511] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Revised: 11/05/2023] [Accepted: 11/20/2023] [Indexed: 12/04/2023] Open
Abstract
Myosin binding protein-C (MyBP-C) is a multidomain protein that regulates muscle contraction. Mutations in MYBPC3, the gene encoding for the cardiac variant (henceforth called cMyBP-C), are amongst the most frequent causes of hypertrophic cardiomyopathy. Most mutations lead to a truncated version of cMyBP-C, which is most likely unstable. However, missense mutations have also been reported, which tend to cluster in the central domains of the cMyBP-C molecule. This suggests that these central domains are more than just a passive spacer between the better characterized N- and C-terminal domains. Here, we investigated the potential impact of four different missense mutations, E542Q, G596R, N755K, and R820Q, which are spread over the domains C3 to C6, on the function of MyBP-C on both the isolated protein level and in cardiomyocytes in vitro. Effect on domain stability, interaction with thin filaments, binding to myosin, and subcellular localization behavior were assessed. Our studies show that these missense mutations result in slightly different phenotypes at the molecular level, which are mutation specific. The expected functional readout of each mutation provides a valid explanation for why cMyBP-C fails to work as a brake in the regulation of muscle contraction, which eventually results in a hypertrophic cardiomyopathy phenotype. We conclude that missense mutations in cMyBP-C must be evaluated in context of their domain localization, their effect on interaction with thin filaments and myosin, and their effect on protein stability to explain how they lead to disease.
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Affiliation(s)
- Amy Pearce
- School of Cardiovascular and Metabolic Medicine and Sciences, King's College London, London, United Kingdom; British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom
| | - Saraswathi Ponnam
- British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom; Randall Centre for Cell and Molecular Biophysics (School of Basic and Biosciences), King's College London, London, United Kingdom
| | - Mark R Holt
- School of Cardiovascular and Metabolic Medicine and Sciences, King's College London, London, United Kingdom; British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom
| | - Thomas Randall
- School of Cardiovascular and Metabolic Medicine and Sciences, King's College London, London, United Kingdom; British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom
| | - Rylan Beckingham
- School of Cardiovascular and Metabolic Medicine and Sciences, King's College London, London, United Kingdom; British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom
| | - Ay Lin Kho
- British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom; Randall Centre for Cell and Molecular Biophysics (School of Basic and Biosciences), King's College London, London, United Kingdom
| | - Thomas Kampourakis
- British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom; Randall Centre for Cell and Molecular Biophysics (School of Basic and Biosciences), King's College London, London, United Kingdom
| | - Elisabeth Ehler
- School of Cardiovascular and Metabolic Medicine and Sciences, King's College London, London, United Kingdom; British Heart Foundation Centre of Research Excellence, King's College London, London, United Kingdom; Randall Centre for Cell and Molecular Biophysics (School of Basic and Biosciences), King's College London, London, United Kingdom.
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5
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Bergonzo C, Aryal B, Rao VA. Divalent ions as mediators of carbonylation in cardiac myosin binding protein C. J Mol Graph Model 2023; 124:108576. [PMID: 37536231 DOI: 10.1016/j.jmgm.2023.108576] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Revised: 07/12/2023] [Accepted: 07/27/2023] [Indexed: 08/05/2023]
Abstract
The dosing and efficacy of chemotherapeutic drugs can be limited by toxicity caused by off-pathway reactions. One hypothesis for how such toxicity arises is via metal-catalyzed oxidative damage of cardiac myosin binding protein C (cMyBP-C) found in cardiac tissue. Previous research indicates that metal ion mediated reactive oxygen species induce high levels of protein carbonylation, changing the structure and function of this protein. In this work, we use long timescale all-atom molecular dynamics simulations to investigate the ion environment surrounding the C0 and C1 subunits of cMyBP-C responsible for actin binding. We show that divalent cations are co-localized with protein carbonylation-prone amino acid residues and that carbonylation of these residues can lead to site-specific interruption to the actin-cMyBP-C binding.
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Affiliation(s)
- Christina Bergonzo
- Institute for Bioscience and Biotechnology Research, National Institute of Standards and Technology, the University of Maryland, 9600 Gudelsky Way, Rockville, MD, 20850, USA.
| | - Baikuntha Aryal
- Laboratory of Applied Biochemistry, Division of Biotechnology Review and Research III, Office of Biotechnology Products, Office of Pharmaceutical Quality, Center for Drug Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, MD, USA
| | - V Ashutosh Rao
- Laboratory of Applied Biochemistry, Division of Biotechnology Review and Research III, Office of Biotechnology Products, Office of Pharmaceutical Quality, Center for Drug Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, MD, USA
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6
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Doh CY, Bharambe N, Holmes JB, Dominic KL, Swanberg CE, Mamidi R, Chen Y, Bandyopadhyay S, Ramachandran R, Stelzer JE. Molecular characterization of linker and loop-mediated structural modulation and hinge motion in the C4-C5 domains of cMyBPC. J Struct Biol 2022; 214:107856. [PMID: 35427781 PMCID: PMC9942529 DOI: 10.1016/j.jsb.2022.107856] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Revised: 03/16/2022] [Accepted: 04/01/2022] [Indexed: 10/18/2022]
Abstract
INTRODUCTION The central C4 and C5 domains (C4C5) of cardiac myosin binding protein C (cMyBPC) contain a flexible interdomain linker and a cardiac-isoform specific loop. However, their importance in the functional regulation of cMyBPC has not been extensively studied. METHODS AND RESULTS We expressed recombinant C4C5 proteins with deleted linker and loop regions and performed biophysical experiments to determine each of their structural and dynamic roles. We show that the linker and C5 loop regions modulate the secondary structure and thermal stability of C4C5. Furthermore, we provide evidence through extended molecular dynamics simulations and principle component analyses that C4C5 can adopt a completely bent or latched conformation. The simulation trajectory and interaction network analyses reveal that the completely bent conformation of C4C5 exhibits a specific pattern of residue-level interactions. Therefore, we propose a "hinge-and-latch" mechanism where the linker allows a great degree of flexibility and bending, while the loop aids in achieving a completely bent and latched conformation. Although this may be one of many bent positions that C4C5 can adopt, we illustrate for the first time in molecular detail that this type of large scale conformational change can occur in the central domains of cMyBPC. CONCLUSIONS Our hinge-and-latch mechanism demonstrates that the linker and loop regions participate in dynamic modulation of cMyBPC's motion and global conformation. These structural and dynamic features may contribute to muscle isoform-specific regulation of actomyosin activity, and have potential implications regarding its ability to propagate or retract cMyBPC's regulatory N-terminal domains.
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Affiliation(s)
- Chang Yoon Doh
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH, USA
| | - Nikhil Bharambe
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH, USA
| | - Joshua B. Holmes
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH, USA
| | - Katherine L. Dominic
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH, USA
| | - Caitlin E. Swanberg
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH, USA
| | - Ranganath Mamidi
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH, USA
| | - Yinghua Chen
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH, USA
| | - Smarajit Bandyopadhyay
- Molecular Biotechnology Core, Shared Laboratory Resources, Cleveland Clinic, Cleveland, OH, USA
| | - Rajesh Ramachandran
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH, USA
| | - Julian E. Stelzer
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH, USA,Corresponding author at: Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, 2109 Adelbert Rd, Robbins E522, Cleveland, OH 44106, USA. (J.E. Stelzer)
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7
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Doh C, Dominic KL, Swanberg CE, Bharambe N, Willard BB, Li L, Ramachandran R, Stelzer JE. Identification of Phosphorylation and Other Post-Translational Modifications in the Central C4C5 Domains of Murine Cardiac Myosin Binding Protein C. ACS OMEGA 2022; 7:14189-14202. [PMID: 35573219 PMCID: PMC9089392 DOI: 10.1021/acsomega.2c00799] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/08/2022] [Accepted: 04/05/2022] [Indexed: 05/06/2023]
Abstract
Cardiac myosin binding protein C (cMyBPC) is a critical multidomain protein that modulates myosin cross bridge behavior and cardiac contractility. cMyBPC is principally regulated by phosphorylation of the residues within the M-domain of its N-terminus. However, not much is known about the phosphorylation or other post-translational modification (PTM) landscape of the central C4C5 domains. In this study, the presence of phosphorylation outside the M-domain was confirmed in vivo using mouse models expressing cMyBPC with nonphosphorylatable serine (S) to alanine substitutions. Purified recombinant mouse C4C5 domain constructs were incubated with 13 different kinases, and samples from the 6 strongest kinases were chosen for mass spectrometry analysis. A total of 26 unique phosphorylated peptides were found, representing 13 different phosphorylation sites including 10 novel sites. Parallel reaction monitoring and subsequent mutagenesis experiments revealed that the S690 site (UniProtKB O70468) was the predominant target of PKA and PKG1. We also report 6 acetylation and 7 ubiquitination sites not previously described in the literature. These PTMs demonstrate the possibility of additional layers of regulation and potential importance of the central domains of cMyBPC in cardiac health and disease. Data are available via ProteomeXchange with identifier PXD031262.
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Affiliation(s)
- Chang
Yoon Doh
- Department
of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, United States
| | - Katherine L. Dominic
- Department
of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, United States
| | - Caitlin E. Swanberg
- Department
of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, United States
| | - Nikhil Bharambe
- Department
of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, United States
| | - Belinda B. Willard
- Proteomics
and Metabolomics Laboratory, Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio 44195, United States
| | - Ling Li
- Proteomics
and Metabolomics Laboratory, Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, Ohio 44195, United States
| | - Rajesh Ramachandran
- Department
of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, United States
| | - Julian E. Stelzer
- Department
of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106, United States
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8
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Microscale thermophoresis suggests a new model of regulation of cardiac myosin function via interaction with cardiac myosin-binding protein C. J Biol Chem 2021; 298:101485. [PMID: 34915024 PMCID: PMC8733265 DOI: 10.1016/j.jbc.2021.101485] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Revised: 11/24/2021] [Accepted: 12/03/2021] [Indexed: 12/02/2022] Open
Abstract
The cardiac isoform of myosin-binding protein C (cMyBP-C) is a key regulatory protein found in cardiac myofilaments that can control the activation state of both the actin-containing thin and myosin-containing thick filaments. However, in contrast to thin filament–based mechanisms of regulation, the mechanism of myosin-based regulation by cMyBP-C has yet to be defined in detail. To clarify its function in this process, we used microscale thermophoresis to build an extensive interaction map between cMyBP-C and isolated fragments of β-cardiac myosin. We show here that the regulatory N-terminal domains (C0C2) of cMyBP-C interact with both the myosin head (myosin S1) and tail domains (myosin S2) with micromolar affinity via phosphorylation-independent and phosphorylation-dependent interactions of domain C1 and the cardiac-specific m-motif, respectively. Moreover, we show that the interaction sites with the highest affinity between cMyBP-C and myosin S1 are localized to its central domains, which bind myosin with submicromolar affinity. We identified two separate interaction regions in the central C2C4 and C5C7 segments that compete for the same binding site on myosin S1, suggesting that cMyBP-C can crosslink the two myosin heads of a single myosin molecule and thereby stabilize it in the folded OFF state. Phosphorylation of the cardiac-specific m-motif by protein kinase A had no effect on the binding of either the N-terminal or the central segments to the myosin head domain, suggesting this might therefore represent a constitutively bound state of myosin associated with cMyBP-C. Based on our results, we propose a new model of regulation of cardiac myosin function by cMyBP-C.
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9
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Wang L, Geist J, Grogan A, Hu LYR, Kontrogianni-Konstantopoulos A. Thick Filament Protein Network, Functions, and Disease Association. Compr Physiol 2018; 8:631-709. [PMID: 29687901 PMCID: PMC6404781 DOI: 10.1002/cphy.c170023] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Sarcomeres consist of highly ordered arrays of thick myosin and thin actin filaments along with accessory proteins. Thick filaments occupy the center of sarcomeres where they partially overlap with thin filaments. The sliding of thick filaments past thin filaments is a highly regulated process that occurs in an ATP-dependent manner driving muscle contraction. In addition to myosin that makes up the backbone of the thick filament, four other proteins which are intimately bound to the thick filament, myosin binding protein-C, titin, myomesin, and obscurin play important structural and regulatory roles. Consistent with this, mutations in the respective genes have been associated with idiopathic and congenital forms of skeletal and cardiac myopathies. In this review, we aim to summarize our current knowledge on the molecular structure, subcellular localization, interacting partners, function, modulation via posttranslational modifications, and disease involvement of these five major proteins that comprise the thick filament of striated muscle cells. © 2018 American Physiological Society. Compr Physiol 8:631-709, 2018.
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Affiliation(s)
- Li Wang
- Department of Biochemistry and Molecular Biology, University of Maryland, Baltimore, Maryland, USA
| | - Janelle Geist
- Department of Biochemistry and Molecular Biology, University of Maryland, Baltimore, Maryland, USA
| | - Alyssa Grogan
- Department of Biochemistry and Molecular Biology, University of Maryland, Baltimore, Maryland, USA
| | - Li-Yen R. Hu
- Department of Biochemistry and Molecular Biology, University of Maryland, Baltimore, Maryland, USA
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10
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Smelter DF, de Lange WJ, Cai W, Ge Y, Ralphe JC. The HCM-linked W792R mutation in cardiac myosin-binding protein C reduces C6 FnIII domain stability. Am J Physiol Heart Circ Physiol 2018; 314:H1179-H1191. [PMID: 29451820 DOI: 10.1152/ajpheart.00686.2017] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Cardiac myosin-binding protein C (cMyBP-C) is a functional sarcomeric protein that regulates contractility in response to contractile demand, and many mutations in cMyBP-C lead to hypertrophic cardiomyopathy (HCM). To gain insight into the effects of disease-causing cMyBP-C missense mutations on contractile function, we expressed the pathogenic W792R mutation (substitution of a highly conserved tryptophan residue by an arginine residue at position 792) in mouse cardiomyocytes lacking endogenous cMyBP-C and studied the functional effects using three-dimensional engineered cardiac tissue constructs (mECTs). Based on complete conservation of tryptophan at this location in fibronectin type II (FnIII) domains, we hypothesized that the W792R mutation affects folding of the C6 FnIII domain, destabilizing the mutant protein. Adenoviral transduction of wild-type (WT) and W792R cDNA achieved equivalent mRNA transcript abundance, but not equivalent protein levels, with W792R compared with WT controls. mECTs expressing W792R demonstrated abnormal contractile kinetics compared with WT mECTs that were nearly identical to cMyBP-C-deficient mECTs. We studied whether common pathways of protein degradation were responsible for the rapid degradation of W792R cMyBP-C. Inhibition of both ubiquitin-proteasome and lysosomal degradation pathways failed to increase full-length mutant protein abundance to WT equivalence, suggesting rapid cytosolic degradation. Bacterial expression of WT and W792R protein fragments demonstrated decreased mutant stability with altered thermal denaturation and increased susceptibility to trypsin digestion. These data suggest that the W792R mutation destabilizes the C6 FnIII domain of cMyBP-C, resulting in decreased full-length protein expression. This study highlights the vulnerability of FnIII-like domains to mutations that alter domain stability and further indicates that missense mutations in cMyBP-C can cause disease through a mechanism of haploinsufficiency. NEW & NOTEWORTHY This study is one of the first to describe a disease mechanism for a missense mutation in cardiac myosin-binding protein C linked to hypertrophic cardiomyopathy. The mutation decreases stability of the fibronectin type III domain and results in substantially reduced mutant protein expression dissonant to transcript abundance.
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Affiliation(s)
- Dan F Smelter
- Department of Pediatrics, University of Wisconsin-Madison , Madison, Wisconsin
| | - Willem J de Lange
- Department of Pediatrics, University of Wisconsin-Madison , Madison, Wisconsin
| | - Wenxuan Cai
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison , Madison, Wisconsin.,Molecular and Cellular Pharmacology Program, University of Wisconsin-Madison , Madison, Wisconsin
| | - Ying Ge
- Department of Cell and Regenerative Biology, University of Wisconsin-Madison , Madison, Wisconsin.,Human Proteomics Program, University of Wisconsin-Madison , Madison, Wisconsin.,Department of Chemistry, School of Medicine and Public Health, University of Wisconsin-Madison , Madison, Wisconsin
| | - J Carter Ralphe
- Department of Pediatrics, University of Wisconsin-Madison , Madison, Wisconsin
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11
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Calcium-Dependent Interaction Occurs between Slow Skeletal Myosin Binding Protein C and Calmodulin. MAGNETOCHEMISTRY 2017. [DOI: 10.3390/magnetochemistry4010001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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12
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Mohamed IA, Krishnamoorthy NT, Nasrallah GK, Da'as SI. The Role of Cardiac Myosin Binding Protein C3 in Hypertrophic Cardiomyopathy-Progress and Novel Therapeutic Opportunities. J Cell Physiol 2017; 232:1650-1659. [PMID: 27731493 DOI: 10.1002/jcp.25639] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2016] [Accepted: 10/07/2016] [Indexed: 11/11/2022]
Abstract
Hypertrophic cardiomyopathy (HCM) is a common autosomal dominant genetic cardiovascular disorder marked by genetic and phenotypic heterogeneity. Mutations in the gene encodes the cardiac myosin-binding protein C, cMYBPC3 is amongst the various sarcomeric genes that are associated with HCM. These mutations produce mutated mRNAs and truncated cMyBP-C proteins. In this review, we will discuss the implications and molecular mechanisms involved in MYBPC3 different mutations. Further, we will highlight the novel targets that can be developed into potential therapeutics for the treatment of HMC. J. Cell. Physiol. 232: 1650-1659, 2017. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Iman A Mohamed
- Department of Biomedical Science, Zewail City of Science and Technology, Giza, Egypt
| | - Navaneethakrishnan T Krishnamoorthy
- Division of Experimental Genetics, Sidra Medical and Research Center, Doha, Qatar.,Heart Science Centre, National Heart and Lung Institute, Imperial College London, London, UK
| | - Gheyath K Nasrallah
- Department of Biomedical Science, College of Health Science, Qatar University, Doha, Qatar.,Biomedical Research Center, Qatar University, Doha, Qatar
| | - Sahar I Da'as
- Division of Experimental Genetics, Sidra Medical and Research Center, Doha, Qatar.,Department of Biomedical and Biological Sciences, Hamad Bin Khalifa University, Doha, Qatar
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13
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The genetic basis of hypertrophic cardiomyopathy in cats and humans. J Vet Cardiol 2016; 17 Suppl 1:S53-73. [PMID: 26776594 DOI: 10.1016/j.jvc.2015.03.001] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2014] [Revised: 01/16/2015] [Accepted: 03/16/2015] [Indexed: 12/19/2022]
Abstract
Mutations in genes that encode for muscle sarcomeric proteins have been identified in humans and two breeds of domestic cats with hypertrophic cardiomyopathy (HCM). This article reviews the history, genetics, and pathogenesis of HCM in the two species in order to give veterinarians a perspective on the genetics of HCM. Hypertrophic cardiomyopathy in people is a genetic disease that has been called a disease of the sarcomere because the preponderance of mutations identified that cause HCM are in genes that encode for sarcomeric proteins (Maron and Maron, 2013). Sarcomeres are the basic contractile units of muscle and thus sarcomeric proteins are responsible for the strength, speed, and extent of muscle contraction. In people with HCM, the two most common genes affected by HCM mutations are the myosin heavy chain gene (MYH7), the gene that encodes for the motor protein β-myosin heavy chain (the sarcomeric protein that splits ATP to generate force), and the cardiac myosin binding protein-C gene (MYBPC3), a gene that encodes for the closely related structural and regulatory protein, cardiac myosin binding protein-C (cMyBP-C). To date, the two mutations linked to HCM in domestic cats (one each in Maine Coon and Ragdoll breeds) also occur in MYBPC3 (Meurs et al., 2005, 2007). This is a review of the genetics of HCM in both humans and domestic cats that focuses on the aspects of human genetics that are germane to veterinarians and on all aspects of feline HCM genetics.
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14
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Kondo T, Hisatome I, Yoshimura S, Mahati E, Notsu T, Li P, Iitsuka K, Kato M, Ogura K, Miake J, Aiba T, Shimizu W, Kurata Y, Sakata S, Nakasone N, Ninomiya H, Nakai A, Higaki K, Kawata Y, Shirayoshi Y, Yoshida A, Yamamoto K. Characterization of the novel mutant A78T-HERG from a long QT syndrome type 2 patient: Instability of the mutant protein and stabilization by heat shock factor 1. J Arrhythm 2016; 32:433-440. [PMID: 27761169 PMCID: PMC5063263 DOI: 10.1016/j.joa.2015.10.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2015] [Revised: 09/10/2015] [Accepted: 10/09/2015] [Indexed: 12/04/2022] Open
Abstract
BACKGROUND The human ether-a-go-go-related gene (HERG) encodes the α-subunit of rapidly activating delayed-rectifier potassium channels. Mutations in this gene cause long QT syndrome type 2 (LQT2). In most cases, mutations reduce the stability of the channel protein, which can be restored by heat shock (HS). METHODS We identified the novel mutant A78T-HERG in a patient with LQT2. The purpose of the current study was to characterize this mutant protein and test whether HS and heat shock factors (HSFs) could stabilize the mutant protein. A78T-HERG and wild-type HERG (WT-HERG) were expressed in HEK293 cells and analyzed by immunoblotting, immunoprecipitation, immunofluorescence, and whole-cell patch clamping. RESULTS When expressed in HEK293 cells, WT-HERG gave rise to immature and mature forms of the protein at 135 and 155 kDa, respectively. A78T-HERG gave rise only to the immature form, which was heavily ubiquitinated. The proteasome inhibitor MG132 increased the expression of immature A78T-HERG and increased both the immature and mature forms of WT-HERG. WT-HERG, but not A78T-HERG, was expressed on the plasma membrane. In whole-cell patch clamping experiments, depolarizing pulses evoked E4031-sensitive HERG channel currents in cells transfected with WT-HERG, but not in cells transfected with A78T-HERG. The A78V mutant, but not A78G mutant, remained in the immature form similarly to A78T. Maturation of the A78T-HERG protein was facilitated by HS, expression of HSF-1, or exposure to geranyl geranyl acetone. CONCLUSIONS A78T-HERG was characterized by protein instability and reduced expression on the plasma membrane. The stability of the mutant was partially restored by HSF-1, indicating that HSF-1 is a target for the treatment for LQT2 caused by the A78T mutation in HERG.
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Affiliation(s)
- Takehito Kondo
- Division of Cardiovascular Medicine, Department of Molecular Medicine and Therapeutics, Faculty of Medicine, Tottori University, Japan
| | - Ichiro Hisatome
- Division of Regenerative Medicine and Therapeutics, Tottori University Graduate School of Medical Science, Japan
| | - Shouichi Yoshimura
- Division of Regenerative Medicine and Therapeutics, Tottori University Graduate School of Medical Science, Japan
| | - Endang Mahati
- Division of Regenerative Medicine and Therapeutics, Tottori University Graduate School of Medical Science, Japan
| | - Tomomi Notsu
- Division of Regenerative Medicine and Therapeutics, Tottori University Graduate School of Medical Science, Japan
| | - Peili Li
- Division of Regenerative Medicine and Therapeutics, Tottori University Graduate School of Medical Science, Japan
| | - Kazuhiko Iitsuka
- Division of Cardiovascular Medicine, Department of Molecular Medicine and Therapeutics, Faculty of Medicine, Tottori University, Japan
| | - Masaru Kato
- Division of Cardiovascular Medicine, Department of Molecular Medicine and Therapeutics, Faculty of Medicine, Tottori University, Japan
| | - Kazuyoshi Ogura
- Division of Cardiovascular Medicine, Department of Molecular Medicine and Therapeutics, Faculty of Medicine, Tottori University, Japan
| | - Junichiro Miake
- Division of Cardiovascular Medicine, Department of Molecular Medicine and Therapeutics, Faculty of Medicine, Tottori University, Japan
| | - Takeshi Aiba
- Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center, Japan
| | - Wataru Shimizu
- Division of Cardiology and Regenerative Medicine, Nippon Medical School, Japan
| | - Yasutaka Kurata
- Department of Physiology II, Kanazawa Medical University, Japan
| | - Shinji Sakata
- Department of Pediatrics, Faculty of Medicine, Tottori University, Japan
| | - Naoe Nakasone
- Department of Biological Regulation, Faculty of Medicine, Tottori University, Japan
| | - Haruaki Ninomiya
- Department of Biological Regulation, Faculty of Medicine, Tottori University, Japan
| | - Akira Nakai
- Department of Biochemistry and Molecular Biology, Yamaguchi University School of Medicine, Japan
| | - Katsumi Higaki
- Division of Functional Genomics, Research Center for Bioscience and Technology, Tottori University, Japan
| | - Yasushi Kawata
- Department of Chemistry and Biotechnology, Graduate School of Engineering, Tottori University, Japan
| | - Yasuaki Shirayoshi
- Division of Regenerative Medicine and Therapeutics, Tottori University Graduate School of Medical Science, Japan
| | - Akio Yoshida
- Division of Regenerative Medicine and Therapeutics, Tottori University Graduate School of Medical Science, Japan
| | - Kazuhiro Yamamoto
- Division of Cardiovascular Medicine, Department of Molecular Medicine and Therapeutics, Faculty of Medicine, Tottori University, Japan
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15
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Phosphorylation and calcium antagonistically tune myosin-binding protein C's structure and function. Proc Natl Acad Sci U S A 2016; 113:3239-44. [PMID: 26908872 DOI: 10.1073/pnas.1522236113] [Citation(s) in RCA: 73] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
During each heartbeat, cardiac contractility results from calcium-activated sliding of actin thin filaments toward the centers of myosin thick filaments to shorten cellular length. Cardiac myosin-binding protein C (cMyBP-C) is a component of the thick filament that appears to tune these mechanochemical interactions by its N-terminal domains transiently interacting with actin and/or the myosin S2 domain, sensitizing thin filaments to calcium and governing maximal sliding velocity. Both functional mechanisms are potentially further tunable by phosphorylation of an intrinsically disordered, extensible region of cMyBP-C's N terminus, the M-domain. Using atomic force spectroscopy, electron microscopy, and mutant protein expression, we demonstrate that phosphorylation reduced the M-domain's extensibility and shifted the conformation of the N-terminal domain from an extended structure to a compact configuration. In combination with motility assay data, these structural effects of M-domain phosphorylation suggest a mechanism for diminishing the functional potency of individual cMyBP-C molecules. Interestingly, we found that calcium levels necessary to maximally activate the thin filament mitigated the structural effects of phosphorylation by increasing M-domain extensibility and shifting the phosphorylated N-terminal fragments back to the extended state, as if unphosphorylated. Functionally, the addition of calcium to the motility assays ablated the impact of phosphorylation on maximal sliding velocities, fully restoring cMyBP-C's inhibitory capacity. We conclude that M-domain phosphorylation may have its greatest effect on tuning cMyBP-C's calcium-sensitization of thin filaments at the low calcium levels between contractions. Importantly, calcium levels at the peak of contraction would allow cMyBP-C to remain a potent contractile modulator, regardless of cMyBP-C's phosphorylation state.
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16
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Nadvi NA, Michie KA, Kwan AH, Guss JM, Trewhella J. Clinically Linked Mutations in the Central Domains of Cardiac Myosin-Binding Protein C with Distinct Phenotypes Show Differential Structural Effects. Structure 2015; 24:105-115. [PMID: 26688216 DOI: 10.1016/j.str.2015.11.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2015] [Revised: 10/28/2015] [Accepted: 11/02/2015] [Indexed: 02/02/2023]
Abstract
The structural effects of three missense mutations clinically linked to hypertrophic cardiomyopathy (HCM) and located in the central domains of cardiac myosin-binding protein C (cMyBP-C) have been determined using small-angle scattering, infrared spectroscopy, and nuclear magnetic resonance spectroscopy. Bioinformatics and modeling were used to initially predict the expected structural impacts and assess the broader implications for function based on sequence conservation patterns. The experimental results generally affirm the predictions that two of the mutations (D745G, P873H) disrupt domain folding, while the third (R820Q) is likely to be entirely solvent exposed and thus more likely to have its impact through its interactions within the sarcomere. Each of the mutations is associated with distinct disease phenotypes, with respect to severity, stage of onset, and end phase. The results are discussed in terms of understanding key structural features of these domains essential for healthy function and the role they may play in disease development.
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Affiliation(s)
- Naveed Ahmed Nadvi
- School of Molecular Bioscience, The University of Sydney, NSW 2006, Australia
| | - Katharine A Michie
- School of Molecular Bioscience, The University of Sydney, NSW 2006, Australia
| | - Ann H Kwan
- School of Molecular Bioscience, The University of Sydney, NSW 2006, Australia
| | - J Mitchell Guss
- School of Molecular Bioscience, The University of Sydney, NSW 2006, Australia
| | - Jill Trewhella
- School of Molecular Bioscience, The University of Sydney, NSW 2006, Australia.
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17
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Ali H, Urolagin S, Gurarslan Ö, Vihinen M. Performance of Protein Disorder Prediction Programs on Amino Acid Substitutions. Hum Mutat 2014; 35:794-804. [DOI: 10.1002/humu.22564] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2013] [Accepted: 04/04/2014] [Indexed: 01/04/2023]
Affiliation(s)
- Heidi Ali
- Institute of Biomedical Technology; FI-33014 University of Tampere; Tampere Finland
- BioMediTech; Tampere Finland
| | - Siddhaling Urolagin
- Department of Experimental Medical Science; Lund University; SE-22184 Lund Sweden
| | - Ömer Gurarslan
- Institute of Biomedical Technology; FI-33014 University of Tampere; Tampere Finland
- BioMediTech; Tampere Finland
| | - Mauno Vihinen
- Institute of Biomedical Technology; FI-33014 University of Tampere; Tampere Finland
- BioMediTech; Tampere Finland
- Department of Experimental Medical Science; Lund University; SE-22184 Lund Sweden
- Tampere University Hospital; Tampere Finland
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18
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Previs MJ, Michalek AJ, Warshaw DM. Molecular modulation of actomyosin function by cardiac myosin-binding protein C. Pflugers Arch 2014; 466:439-44. [PMID: 24407948 PMCID: PMC3932558 DOI: 10.1007/s00424-013-1433-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Accepted: 12/23/2013] [Indexed: 11/29/2022]
Abstract
Cardiac myosin-binding protein C is a key regulator of cardiac contractility and is capable of both activating the thin filament to initiate actomyosin motion generation and governing maximal sliding velocities. While MyBP-C's C terminus localizes the molecule within the sarcomere, the N terminus appears to confer regulatory function by binding to the myosin motor domain and/or actin. Literature pertaining to how MyBP-C binding to the myosin motor domain and or actin leads to MyBP-C's dual modulatory roles that can impact actomyosin interactions are discussed.
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Affiliation(s)
- Michael J Previs
- Department of Molecular Physiology & Biophysics, University of Vermont, 149 Beaumont Ave., HSRF Building Rm.-116, Burlington, VT, 05405, USA
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19
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Finley NL, Cuperman TI. Cardiac myosin binding protein-C: a structurally dynamic regulator of myocardial contractility. Pflugers Arch 2014; 466:433-8. [PMID: 24469349 DOI: 10.1007/s00424-014-1451-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2013] [Revised: 01/10/2014] [Accepted: 01/14/2014] [Indexed: 11/28/2022]
Abstract
Cardiac myosin binding protein-C (cMyBP-C) is a modular protein anchored to the thick filament through interactions mediated by its C-terminal region. The N-terminal region of cMyBPC-C regulates myocardial contractility by modifying actin-myosin association. Phosphorylation of the N-terminal region diminishes cMyBP-C's capacity to regulate actin-myosin function. Despite a substantial body of literature, many issues remain unclear regarding the structural and functional roles of cMyBP-C. While no high-resolution structures of the intact protein exist, crystallographic and nuclear magnetic resonance (NMR) structures of isolated N-terminal domains provide important molecular details regarding cMyBP-C's role in controlling contractility. In this review, we summarize the emerging structural understanding of cMyBP-C with a particular emphasis placed on describing how its dynamic molecular interactions with both thin and thick filament proteins likely contribute to contractile regulation. Furthermore, we discuss the future directions and strategies by which we may improve the mechanistic understanding of its role in modulating cardiac muscle contraction.
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Affiliation(s)
- Natosha L Finley
- The Cell, Molecular, and Structural Biology Program, Department of Microbiology, Miami University, 700 East High Street, 32 Pearson Hall, Oxford, OH, 45056, USA,
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20
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Gajendrarao P, Krishnamoorthy N, Kassem HS, Moharem-Elgamal S, Cecchi F, Olivotto I, Yacoub MH. Molecular modeling of disease causing mutations in domain C1 of cMyBP-C. PLoS One 2013; 8:e59206. [PMID: 23527136 PMCID: PMC3602012 DOI: 10.1371/journal.pone.0059206] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2012] [Accepted: 02/12/2013] [Indexed: 11/20/2022] Open
Abstract
Cardiac myosin binding protein-C (cMyBP-C) is a multi-domain (C0-C10) protein that regulates heart muscle contraction through interaction with myosin, actin and other sarcomeric proteins. Several mutations of this protein cause familial hypertrophic cardiomyopathy (HCM). Domain C1 of cMyBP-C plays a central role in protein interactions with actin and myosin. Here, we studied structure-function relationship of three disease causing mutations, Arg177His, Ala216Thr and Glu258Lys of the domain C1 using computational biology techniques with its available X-ray crystal structure. The results suggest that each mutation could affect structural properties of the domain C1, and hence it's structural integrity through modifying intra-molecular arrangements in a distinct mode. The mutations also change surface charge distributions, which could impact the binding of C1 with other sarcomeric proteins thereby affecting contractile function. These structural consequences of the C1 mutants could be valuable to understand the molecular mechanisms for the disease.
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Affiliation(s)
| | | | - Heba Sh Kassem
- BA-HCM National Programme at Aswan Heart Centre, Egypt
- Pathology Department and Clinical Genomics Centre, Alexandria Faculty of Medicine, Alexandria, Egypt
| | - Sarah Moharem-Elgamal
- BA-HCM National Programme at Aswan Heart Centre, Egypt
- National Heart Institute, Giza, Egypt
| | - Franco Cecchi
- Referral Center for Myocardial Diseases, Careggi University Hospital, Florence, Italy
| | - Iacopo Olivotto
- Referral Center for Myocardial Diseases, Careggi University Hospital, Florence, Italy
| | - Magdi H. Yacoub
- Qatar Cardiovascular Research Center, Qatar Foundation, Doha, Qatar
- BA-HCM National Programme at Aswan Heart Centre, Egypt
- National Heart and Lung Institute, Imperial College London, United Kingdom
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21
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Jeffries CM, Lu Y, Hynson RMG, Taylor JEN, Ballesteros M, Kwan AH, Trewhella J. Human cardiac myosin binding protein C: structural flexibility within an extended modular architecture. J Mol Biol 2011; 414:735-48. [PMID: 22041450 DOI: 10.1016/j.jmb.2011.10.029] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2011] [Revised: 10/15/2011] [Accepted: 10/18/2011] [Indexed: 10/15/2022]
Abstract
New insights into the modular organization and flexibility of the N-terminal half of human cardiac myosin binding protein C (cMyBP-C) and information on the association state of the full-length protein have been deduced from a combined small-angle X-ray scattering (SAXS) and NMR study. SAXS data show that the first five immunoglobulin domains of cMyBP-C, which include those implicated in interactions with both myosin and actin, remain monodisperse and monomeric in solution and have a highly extended yet distinctively 'bent' modular arrangement that is similar to the giant elastic muscle protein titin. Analyses of the NMR and SAXS data indicate that a proline/alanine-rich linker connecting the cardiac-specific N-terminal C0 domain to the C1 domain provides significant structural flexibility at the N-terminus of the human isoform, while the modular arrangement of domains C1-C2-C3-C4 is relatively fixed. Domain fragments from the C-terminal half of the protein have a propensity to self-associate in vitro, while full-length bacterially expressed cMyBP-C forms flexible extended dimers at micromolar protein concentrations. In summary, our studies reveal that human cMyBP-C combines a distinctive modular architecture with regions of flexibility and that the N-terminal half of the protein is sufficiently extended to span the range of interfilament distances sampled within the dynamic environment of heart muscle. These structural features of cMyBP-C could facilitate its putative role as a molecular switch between actin and myosin and may contribute to modulating the transverse pliancy of the C-zone of the A-band across muscle sarcomeres.
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Affiliation(s)
- Cy M Jeffries
- School of Molecular Bioscience, University of Sydney, New South Wales 2006, Australia
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22
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Abstract
In the 20 years since the discovery of the first mutation linked to familial hypertrophic cardiomyopathy (HCM), an astonishing number of mutations affecting numerous sarcomeric proteins have been described. Among the most prevalent of these are mutations that affect thick filament binding proteins, including the myosin essential and regulatory light chains and cardiac myosin binding protein (cMyBP)-C. However, despite the frequency with which myosin binding proteins, especially cMyBP-C, have been linked to inherited cardiomyopathies, the functional consequences of mutations in these proteins and the mechanisms by which they cause disease are still only partly understood. The purpose of this review is to summarize the known disease-causing mutations that affect the major thick filament binding proteins and to relate these mutations to protein function. Conclusions emphasize the impact that discovery of HCM-causing mutations has had on fueling insights into the basic biology of thick filament proteins and reinforce the idea that myosin binding proteins are dynamic regulators of the activation state of the thick filament that contribute to the speed and force of myosin-driven muscle contraction. Additional work is still needed to determine the mechanisms by which individual mutations induce hypertrophic phenotypes.
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Affiliation(s)
- Samantha P Harris
- Department of Neurobiology, Physiology, and Behavior College of Biological Sciences, University of California, One Shields Ave, Davis, CA 95616, USA.
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23
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Ratti J, Rostkova E, Gautel M, Pfuhl M. Structure and interactions of myosin-binding protein C domain C0: cardiac-specific regulation of myosin at its neck? J Biol Chem 2011; 286:12650-8. [PMID: 21297165 PMCID: PMC3069465 DOI: 10.1074/jbc.m110.156646] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Myosin-binding protein C (MyBP-C) is a multidomain protein present in the thick filaments of striated muscles and is involved in both sarcomere formation and contraction regulation. The latter function is believed to be located at the N terminus, which is close to the motor domain of myosin. The cardiac isoform of MyBP-C is linked to hypertrophic cardiomyopathy. Here, we use NMR spectroscopy and biophysical and biochemical assays to study the three-dimensional structure and interactions of the cardiac-specific Ig-like domain C0, a part of cardiac MyBP-C of which little is known. The structure confirmed that C0 is a member of the IgI class of proteins, showing many of the characteristic features of this fold. Moreover, we identify a novel interaction between C0 and the regulatory light chain of myosin, thus placing the N terminus of the protein in proximity to the motor domain of myosin. This novel interaction is disrupted by several cardiomyopathy-linked mutations in the MYBPC3 gene. These results provide new insights into how cardiac MyBP-C incorporates in the sarcomere and how it can contribute to the regulation of muscle contraction.
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Affiliation(s)
- Joyce Ratti
- Department of Biochemistry, University of Leicester, Lancaster Road, Leicester LE1 9HN, UK
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24
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Tvorogov D, Anisimov A, Zheng W, Leppänen VM, Tammela T, Laurinavicius S, Holnthoner W, Heloterä H, Holopainen T, Jeltsch M, Kalkkinen N, Lankinen H, Ojala PM, Alitalo K. Effective suppression of vascular network formation by combination of antibodies blocking VEGFR ligand binding and receptor dimerization. Cancer Cell 2010; 18:630-40. [PMID: 21130043 DOI: 10.1016/j.ccr.2010.11.001] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/12/2010] [Revised: 09/21/2010] [Accepted: 10/28/2010] [Indexed: 02/06/2023]
Abstract
Antibodies that block vascular endothelial growth factor (VEGF) have become an integral part of antiangiogenic tumor therapy, and antibodies targeting other VEGFs and receptors (VEGFRs) are in clinical trials. Typically receptor-blocking antibodies are targeted to the VEGFR ligand-binding site. Here we describe a monoclonal antibody that inhibits VEGFR-3 homodimer and VEGFR-3/VEGFR-2 heterodimer formation, signal transduction, as well as ligand-induced migration and sprouting of microvascular endothelial cells. Importantly, we show that combined use of antibodies blocking ligand binding and receptor dimerization improves VEGFR inhibition and results in stronger inhibition of endothelial sprouting and vascular network formation in vivo. These results suggest that receptor dimerization inhibitors could be used to enhance antiangiogenic activity of antibodies blocking ligand binding in tumor therapy.
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Affiliation(s)
- Denis Tvorogov
- Institute for Molecular Medicine Finland, Department of Pathology, Haartman Institute, Helsinki University Central Hospital, University of Helsinki, Finland
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25
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Rybakova IN, Greaser ML, Moss RL. Myosin binding protein C interaction with actin: characterization and mapping of the binding site. J Biol Chem 2010; 286:2008-16. [PMID: 21071444 DOI: 10.1074/jbc.m110.170605] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Myosin binding protein C (MyBPC) is a multidomain protein associated with the thick filaments of striated muscle. Although both structural and regulatory roles have been proposed for MyBPC, its interactions with other sarcomeric proteins remain obscure. The current study was designed to examine the actin-binding properties of MyBPC and to define MyBPC domain regions involved in actin interaction. Here, we have expressed full-length mouse cardiac MyBPC (cMyBPC) in a baculovirus system and shown that purified cMyBPC binds actin filaments with an affinity of 4.3 ± 1.1 μM and a 1:1 molar ratio with regard to an actin protomer. The actin binding by cMyBPC is independent of protein phosphorylation status and is not significantly affected by the presence of tropomyosin and troponin on the actin filament. In addition, cMyBPC-actin interaction is not modulated by calmodulin. To determine the region of cMyBPC that is responsible for its interaction with actin, we have expressed and characterized five recombinant proteins encoding fragments of the cMyBPC sequence. Recombinant N-terminal fragments such as C0-C1, C0-C4, and C0-C5 cosediment with actin in a linear, nonsaturable manner. At the same time, MyBPC fragments lacking either the C0-C1 or C0-C4 region bind F-actin with essentially the same properties as full-length protein. Together, our results indicate that cMyBPC interacts with actin via a single, moderate affinity site localized to the C-terminal region of the protein. In contrast, certain basic regions of the N-terminal domains of MyBPC may act as small polycations and therefore bind actin via nonspecific electrostatic interactions.
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Affiliation(s)
- Inna N Rybakova
- Department of Physiology, University of Wisconsin Medical School, Madison, Wisconsin 53706, USA.
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26
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Bahrudin U, Morisaki H, Morisaki T, Ninomiya H, Higaki K, Nanba E, Igawa O, Takashima S, Mizuta E, Miake J, Yamamoto Y, Shirayoshi Y, Kitakaze M, Carrier L, Hisatome I. Ubiquitin-proteasome system impairment caused by a missense cardiac myosin-binding protein C mutation and associated with cardiac dysfunction in hypertrophic cardiomyopathy. J Mol Biol 2008; 384:896-907. [PMID: 18929575 DOI: 10.1016/j.jmb.2008.09.070] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2008] [Revised: 09/09/2008] [Accepted: 09/22/2008] [Indexed: 11/19/2022]
Abstract
The ubiquitin-proteasome system is responsible for the disappearance of truncated cardiac myosin-binding protein C, and the suppression of its activity contributes to cardiac dysfunction. This study investigated whether missense cardiac myosin-binding protein C gene (MYBPC3) mutation in hypertrophic cardiomyopathy (HCM) leads to destabilization of its protein, causes UPS impairment, and is associated with cardiac dysfunction. Mutations were identified in Japanese HCM patients using denaturing HPLC and sequencing. Heterologous expression was investigated in COS-7 cells as well as neonatal rat cardiac myocytes to examine protein stability and proteasome activity. The cardiac function was measured using echocardiography. Five novel MYBPC3 mutations -- E344K, DeltaK814, Delta2864-2865GC, Q998E, and T1046M -- were identified in this study. Compared with the wild type and other mutations, the E334K protein level was significantly lower, it was degraded faster, it had a higher level of polyubiquination, and increased in cells pretreated with the proteasome inhibitor MG132 (50 microM, 6 h). The electrical charge of its amino acid at position 334 influenced its stability, but E334K did not affect its phosphorylation. The E334K protein reduced cellular 20 S proteasome activity, increased the proapoptotic/antiapoptotic protein ratio, and enhanced apoptosis in transfected Cos-7 cells and neonatal rat cardiac myocytes. Patients carrying the E334K mutation presented significant left ventricular dysfunction and dilation. The conclusion is the missense MYBPC3 mutation E334K destabilizes its protein through UPS and may contribute to cardiac dysfunction in HCM through impairment of the ubiquitin-proteasome system.
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Affiliation(s)
- Udin Bahrudin
- Division of Regenerative Medicine and Therapeutics, Institute of Regenerative Medicine and Biofunction, Tottori University Graduate School of Medical Science, Yonago, Japan
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Analyzing pathogenic mutations of C5 domain from cardiac myosin binding protein C through MD simulations. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2008; 37:683-91. [DOI: 10.1007/s00249-008-0308-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2007] [Revised: 02/04/2008] [Accepted: 03/10/2008] [Indexed: 11/26/2022]
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28
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Stability and kinetic properties of C5-domain from myosin binding protein C and its mutants. Biophys J 2007; 94:1403-11. [PMID: 17965135 DOI: 10.1529/biophysj.107.106625] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The impact of three mutations of domain C5 from myosin binding protein C, correlated to Familial Hypertrophic Cardiomyopathy, has been assessed through molecular dynamics simulations based on a native centric protein modeling. The severity of the phenotype correlates with the shift in unfolding temperature determined by the mutations. A contact probability analysis reveals a folding process of the C5 domain originating in the region of DE and FG loops and propagating toward the area proximal to CD and EF loops. This suggests that mutation effects gain relevance in the proximity to the area where folding originates. The scenario is also confirmed by the analysis of the kinetics of 27 test mutations evenly distributed throughout the entire C5 domain.
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29
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Guardiani C, Cecconi F, Livi R. Computational analysis of folding and mutation properties of C5 domain of myosin binding protein C. Proteins 2007; 70:1313-22. [PMID: 17876814 DOI: 10.1002/prot.21621] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Thermal folding molecular dynamics simulations of the domain C5 of Myosin binding protein C were performed using a native-centric model to study the role of three mutations related to Familial Hypertrophic Cardiomyopathy. Mutation of Asn755 causes the largest shift of the folding temperature, and the residue is located in the CFGA' beta-sheet featuring the highest phi-values. The mutation thus appears to reduce the thermodynamic stability in agreement with experimental data. The mutations on Arg654 and Arg668, conversely, cause little change in the folding temperature and they reside in the low phi-value BDE beta-sheet, so that their pathological role cannot be related to impairment of the folding process but possibly to the binding with target molecules. As the typical signature of Domain C5 is the presence of a longer and destibilizing CD-loop with respect to the other Ig-like domains, we completed the work with a bioinformatic analysis of this loop showing a high density of negative charge and low hydrophobicity. This indicates the CD-loop as a natively unfolded sequence with a likely coupling between folding and ligand binding.
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Affiliation(s)
- Carlo Guardiani
- Centro Interdipartimentale per lo Studio delle Dinamiche Complesse Sezione INFN di Firenze, Italy
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Kulikovskaya I, McClellan GB, Levine R, Winegrad S. Multiple forms of cardiac myosin-binding protein C exist and can regulate thick filament stability. ACTA ACUST UNITED AC 2007; 129:419-28. [PMID: 17470661 PMCID: PMC2154376 DOI: 10.1085/jgp.200609714] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Although absence or abnormality of cardiac myosin binding protein C (cMyBP-C) produces serious structural and functional abnormalities of the heart, function of the protein itself is not clearly understood, and the cause of the abnormalities, unidentified. Here we report that a major function of cMyBP-C may be regulating the stability of the myosin-containing contractile filaments through phosphorylation of cMyBP-C. Antibodies were raised against three different regions of cMyBP-C to detect changes in structure within the molecule, and loss of myosin heavy chain was used to monitor degradation of the thick filament. Results from Western blotting and polyacrylamide gel electrophoresis indicate that cMyBP-C can exist in two different forms that produce, respectively, stable and unstable thick filaments. The stable form has well-ordered myosin heads and requires phosphorylation of the cMyBP-C. The unstable form has disordered myosin heads. In tissue with intact cardiac cells, the unstable unphosphorylated cMyBP-C is more easily proteolyzed, causing thick filaments first to release cMyBP-C and/or its proteolytic peptides and then myosin. Filaments deficient in cMyBP-C are fragmented by shear force well tolerated by the stable form. We hypothesize that modulation of filament stability can be coupled at the molecular level with the strength of contraction by the sensitivity of each to the concentration of calcium ions.
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Affiliation(s)
- Irina Kulikovskaya
- Department of Physiology, University of Philadelphia School of Medicine, Philadelphia, PA 19104, USA.
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31
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Ababou A, Gautel M, Pfuhl M. Dissecting the N-terminal Myosin Binding Site of Human Cardiac Myosin-binding Protein C. J Biol Chem 2007; 282:9204-15. [PMID: 17192269 DOI: 10.1074/jbc.m610899200] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Myosin-binding protein C (MyBP-C) binds to myosin with two binding sites, one close to the N terminus and the other at the C terminus. Here we present the solution structure of one part of the N-terminal binding site, the third immunoglobulin domain of the cardiac isoform of human MyBP-C (cC2) together with a model of its interaction with myosin. Domain cC2 has the beta-sandwich structure expected from a member of the immunoglobulin fold. The C-terminal part of the structure of cC2 is very closely related to telokin, the myosin binding fragment of myosin light chain kinase. Domain cC2 also contains two cysteines on neighboring strands F and G, which would be able to form a disulfide bridge in a similar position as in telokin. Using NMR spectroscopy and isothermal titration calorimetry we demonstrate that cC2 alone binds to a fragment of myosin, S2Delta, with low affinity (kD = 1.1 mM) but exhibits a highly specific binding site. This consists of the C-terminal surface of the C'CFGA' beta-sheet, which includes Glu(301), a residue mutated to Gln in the disease familial hypertrophic cardiomyopathy. The binding site on S2 was identified by a combination of NMR binding experiments of cC2 with S2Delta containing the cardiomyopathy-linked mutation R870H and molecular modeling. This mutation lowers the binding affinity and changes the arrangement of side chains at the interface. Our model of the cC2-S2Delta complex gives a first glimpse of details of the MyBP-C-myosin interaction. Using this model we suggest that most key interactions are between polar amino acids, explaining why the mutations E301Q in cC2 and R870H in S2Delta could be involved in cardiomyopathy. We expect that this model will stimulate future research to further refine the details of this interaction and their importance for cardiomyopathy.
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Affiliation(s)
- Abdessamad Ababou
- Department of Biochemistry, University of Leicester, University Road, Leicester LE1 7RH
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32
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Konno T, Shimizu M, Ino H, Fujino N, Uchiyama K, Mabuchi T, Sakata K, Kaneda T, Fujita T, Masuta E, Mabuchi H. A novel mutation in the cardiac myosin-binding protein C gene is responsible for hypertrophic cardiomyopathy with severe ventricular hypertrophy and sudden death. Clin Sci (Lond) 2005; 110:125-31. [PMID: 16181148 DOI: 10.1042/cs20050189] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
It has been demonstrated previously that clinical phenotypes of HCM (hypertrophic cardiomyopathy) caused by mutations in the cardiac MyBP-C (myosin-binding protein C) gene show late onset, low penetrance and favourable clinical course. However, we have encountered severe phenotypes in several carriers of the MyBP-C gene mutations. The aim of the present study was to screen novel MyBP-C gene mutations in patients with HCM and to investigate the genetic differences in affected subjects with severe phenotypes. The MyBP-C gene was screened in 292 Japanese probands with HCM, and a novel c.2067+1G→A mutation was present in 15 subjects in five families. Clinical phenotypes of carriers of the c.2067+1G→A mutation were compared with those of a previously identified Arg820Gln (Arg820→Gln) mutation in the MyBP-C gene. The disease penetrance in subjects aged ≥30 years was 90% in carriers of the c.2067+1G→A mutation and 61% in carriers of the Arg820Gln mutation. Sudden death occurred in four subjects from three families with the c.2067+1G→A mutation and in two subjects from one family with the Arg820Gln mutation. Two carriers of the c.2067+1G→A mutation had substantial hypertrophy (maximal wall thickness ≥30 mm). In contrast, two carriers of the Arg820Gln mutation had end-stage HCM. In conclusion, the c.2067+1G→A mutation is associated with HCM with substantial hypertrophy and moderate incidence of sudden death, whereas the Arg820Gln mutation is associated with end-stage HCM. These observations may provide important prognostic information regarding the clinical practice of HCM.
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Affiliation(s)
- Tetsuo Konno
- Molecular Genetics of Cardiovascular Disorders, Division of Cardiovascular Medicine, Graduate School of Medical Science, Kanazawa University, Takara-machi 13-1, Kanazawa 920-8640, Japan.
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33
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Oakley CE, Hambly BD, Curmi PMG, Brown LJ. Myosin binding protein C: structural abnormalities in familial hypertrophic cardiomyopathy. Cell Res 2004; 14:95-110. [PMID: 15115610 DOI: 10.1038/sj.cr.7290208] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The muscle protein myosin binding protein C (MyBPC) is a large multi-domain protein whose role in the sarcomere is complex and not yet fully understood. Mutations in MyBPC are strongly associated with the heart disease familial hypertrophic cardiomyopathy (FHC) and these experiments of nature have provided some insight into the intricate workings of this protein in the heart. While some regions of the MyBPC molecule have been assigned a function in the regulation of muscle contraction, the interaction of other regions with various parts of the myosin molecule and the sarcomeric proteins, actin and titin, remain obscure. In addition, several intra-domain interactions between adjacent MyBPC molecules have been identified. Although the basic structure of the molecule (a series of immunoglobulin and fibronectin domains) has been elucidated, the assembly of MyBPC in the sarcomere is a topic for debate. By analysing the MyBPC sequence with respect to FHC-causing mutations it is possible to identify individual residues or regions of each domain that may be important either for binding or regulation. This review looks at the current literature, in concert with alignments and the structural models of MyBPC, in an attempt to understand how FHC mutations may lead to the disease state.
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Affiliation(s)
- Cecily E Oakley
- Department of Pathology, University of Sydney, NSW 2006, Australia.
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Nicastro G, Margiocco P, Cardinali B, Stagnaro P, Cauglia F, Cuniberti C, Collini M, Thomas D, Pastore A, Rocco M. The role of unstructured extensions in the rotational diffusion properties of a globular protein: the example of the titin i27 module. Biophys J 2004; 87:1227-40. [PMID: 15298925 PMCID: PMC1304461 DOI: 10.1529/biophysj.104.040931] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2004] [Accepted: 05/14/2004] [Indexed: 11/18/2022] Open
Abstract
The possibility of predicting the overall shape of a macromolecule in solution from its diffusional properties has gained increasing importance in the structural genomic era. Here we explore and quantify the influence that unstructured and flexible regions have on the motions of a globular protein, a situation that can occur from the presence of such regions in the natural sequence or from additional tags. I27, an immunoglobulin-like module from the muscle protein titin, whose structure and properties are well characterized, was selected for our studies. The backbone dynamics and the overall tumbling of three different constructs of I27 were investigated using (15)N NMR relaxation collected at two (15)N frequencies (60.8 and 81.1 MHz) and fluorescence depolarization spectroscopy after labeling of a reactive cysteine with an extrinsic fluorophore. Our data show that the presence of disordered tags clearly exerts a frictional drag that increases with the length of the tags, thus affecting the module tumbling in solution. We discuss the use and the limitations of current approaches to hydrodynamic calculations, especially when having to take into account local flexibility.
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35
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Abstract
Myosin binding protein-C (MyBP-C) is a thick filament–associated protein localized to the crossbridge-containing C zones of striated muscle sarcomeres. The cardiac isoform is composed of eight immunoglobulin I–like domains and three fibronectin 3–like domains and is known to be a physiological substrate of cAMP-dependent protein kinase. MyBP-C contributes to thick filament structure via interactions at its C-terminus with the light meromyosin section of the myosin rod and with titin. The protein also has a role in the regulation of contraction, due to the binding of its N-terminus to the subfragment-2 portion of myosin, which reduces actomyosin ATPase activity; phosphorylation abolishes this interaction, resulting in release of the “brake” on crossbridge cycling. Several structural models of the interaction of MyBP-C with myosin have been proposed, although its precise arrangement on the thick filament remains to be elucidated. Mutations in the gene encoding cardiac MyBP-C are a common cause of hypertrophic cardiomyopathy, and this has led to increased interest in the protein’s function. Investigation of disease-causing mutations in domains with unknown function has led to further insights into the mechanism of cMyBP-C action. This Review aims to collate the published data on those aspects of MyBP-C that are well characterized and to consider new and emerging data that further define its structural and regulatory roles and its arrangement in the sarcomere. We also speculate on the mechanisms by which hypertrophic cardiomyopathy–causing truncation and missense mutations affect the normal functioning of the sarcomere.
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Affiliation(s)
- Emily Flashman
- Department of Cardiovascular Medicine, University of Oxford, UK
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