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Guo H, Zhao Q, Wang H, Zhu S, Dong H, Xie X, Wang L, Chen L, Han H. Molecular characterization and functional analysis of Eimeria tenella ankyrin repeat-containing protein. Eur J Protistol 2024; 94:126089. [PMID: 38749182 DOI: 10.1016/j.ejop.2024.126089] [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: 02/21/2024] [Revised: 05/06/2024] [Accepted: 05/07/2024] [Indexed: 06/14/2024]
Abstract
Chicken coccidiosis causes disastrous losses to the poultry industry all over the world. Eimeria tenella is the most prevalent of these disease-causing species. Our former RNA-seq indicated that E. tenella ankyrin repeat-containing protein (EtANK) was expressed differently between drug-sensitive (DS) and drug-resistant strains. In this study, we cloned EtANK and analyzed its translational and transcriptional levels using quantitative real-time PCR (qPCR) and western blotting. The data showed that EtANK was significantly upregulated in diclazuril-resistant (DZR) strain and maduramicin-resistant (MRR) strain compared with the drug-sensitive (DS) strain. In addition, the transcription levels in the DZR strains isolated from the field were higher than in the DS strain. The translation levels of EtANK were higher in unsporulated oocysts (UO) than in sporozoites (SZ), sporulated oocysts (SO), or second-generation merozoites (SM), and the protein levels in SM were significantly higher than in UO, SO, and SZ. The results of the indirect immunofluorescence localization showed that the protein was distributed mainly at the anterior region of SZ and on the surface and in the cytoplasm of SM. The fluorescence intensity increased further with its development in vitro. An anti-rEtANK polyclonal antibody inhibited the invasive ability of E. tenella in DF-1 cells. These results showed that EtANK may be related to host cell invasion, required for the parasite's growth in the host, and may be involved in the development of E. tenella resistance to some drugs.
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Affiliation(s)
- Huilin Guo
- Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Key Laboratory of Animal Parasitology of Ministry of Agriculture, Minhang, Shanghai 200241, PR China
| | - Qiping Zhao
- Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Key Laboratory of Animal Parasitology of Ministry of Agriculture, Minhang, Shanghai 200241, PR China
| | - Haixia Wang
- Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Key Laboratory of Animal Parasitology of Ministry of Agriculture, Minhang, Shanghai 200241, PR China
| | - Shunhai Zhu
- Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Key Laboratory of Animal Parasitology of Ministry of Agriculture, Minhang, Shanghai 200241, PR China
| | - Hui Dong
- Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Key Laboratory of Animal Parasitology of Ministry of Agriculture, Minhang, Shanghai 200241, PR China
| | - Xinrui Xie
- Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Key Laboratory of Animal Parasitology of Ministry of Agriculture, Minhang, Shanghai 200241, PR China
| | - Lihui Wang
- Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Key Laboratory of Animal Parasitology of Ministry of Agriculture, Minhang, Shanghai 200241, PR China
| | - Lang Chen
- Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Key Laboratory of Animal Parasitology of Ministry of Agriculture, Minhang, Shanghai 200241, PR China
| | - Hongyu Han
- Shanghai Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Key Laboratory of Animal Parasitology of Ministry of Agriculture, Minhang, Shanghai 200241, PR China.
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2
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Sun Y, Liu X, Huang W, Le S, Yan J. Structural domain in the Titin N2B-us region binds to FHL2 in a force-activation dependent manner. Nat Commun 2024; 15:4496. [PMID: 38802383 DOI: 10.1038/s41467-024-48828-7] [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: 03/31/2022] [Accepted: 05/15/2024] [Indexed: 05/29/2024] Open
Abstract
Titin N2B unique sequence (N2B-us) is a 572 amino acid sequence that acts as an elastic spring to regulate muscle passive elasticity. It is thought to lack stable tertiary structures and is a force-bearing region that is regulated by mechanical stretching. In this study, the conformation of N2B-us and its interaction with four-and-a-half LIM domain protein 2 (FHL2) are investigated using AlphaFold2 predictions and single-molecule experimental validation. Surprisingly, a stable alpha/beta structural domain is predicted and confirmed in N2B-us that can be mechanically unfolded at forces of a few piconewtons. Additionally, more than twenty FHL2 LIM domain binding sites are predicted to spread throughout N2B-us. Single-molecule manipulation experiments reveals the force-dependent binding of FHL2 to the N2B-us structural domain. These findings provide insights into the mechano-sensing functions of N2B-us and its interactions with FHL2.
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Affiliation(s)
- Yuze Sun
- Mechanobiology Institute, National University of Singapore, Singapore, Singapore
| | - Xuyao Liu
- Department of Physics, National University of Singapore, Singapore, Singapore
| | - Wenmao Huang
- Department of Physics, National University of Singapore, Singapore, Singapore
| | - Shimin Le
- Department of Physics, National University of Singapore, Singapore, Singapore
| | - Jie Yan
- Mechanobiology Institute, National University of Singapore, Singapore, Singapore.
- Department of Physics, National University of Singapore, Singapore, Singapore.
- Centre for Biological Imaging Sciences, National University of Singapore, Singapore, Singapore.
- Joint School of National University of Singapore and Tianjin University, International Campus of Tianjin University, Binhai New City, Fuzhou, China.
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3
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Stehle J, Fleming JR, Bauer PM, Mayans O, Drescher M. Titin UN2A Acts as a Stable, Non-Polymorphic Scaffold in its Binding to CARP. Chembiochem 2023; 24:e202300408. [PMID: 37503755 DOI: 10.1002/cbic.202300408] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 07/25/2023] [Accepted: 07/27/2023] [Indexed: 07/29/2023]
Abstract
The N2A segment of titin functions as a pivotal hub for signal transduction and interacts with various proteins involved in structural support, chaperone activities, and transcriptional regulation. Notably, the "unique N2A" (UN2A) subdomain has been shown to interact with the stress-regulated cardiac ankyrin repeat protein (CARP), which contributes to the regulation of sarcomeric stiffness. Previously, the UN2A domain's three-dimensional structure was modelled based on its secondary structure content identified by NMR spectroscopy, considering the domain in isolation. In this study, we report experimental long-range distance distributions by electron paramagnetic resonance (EPR) spectroscopy between the three helixes within the UN2A domain linked to the immunoglobulin domain I81 in the presence and absence of CARP. The data confirm the central three-helix bundle fold of UN2A and show that this adopts a compact and stable conformation in absence of CARP. After binding to CARP, no significant conformational change was observed, suggesting that the UN2A domain retains its structure upon binding to CARP thereby, mediating the interaction approximately as a rigid-body.
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Affiliation(s)
- Juliane Stehle
- Department of Chemistry and Konstanz Research School of Chemical Biology (KoRS-CB), University of Konstanz, Universitätsstraße 10, 78457, Konstanz, Germany
| | - Jennifer R Fleming
- Department of Biology, University of Konstanz, Universitätsstraße 10, 78457, Konstanz, Germany
| | - Piera-Maria Bauer
- Department of Biology, University of Konstanz, Universitätsstraße 10, 78457, Konstanz, Germany
| | - Olga Mayans
- Department of Biology, University of Konstanz, Universitätsstraße 10, 78457, Konstanz, Germany
| | - Malte Drescher
- Department of Chemistry and Konstanz Research School of Chemical Biology (KoRS-CB), University of Konstanz, Universitätsstraße 10, 78457, Konstanz, Germany
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4
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Bang ML, Bogomolovas J, Chen J. Understanding the molecular basis of cardiomyopathy. Am J Physiol Heart Circ Physiol 2022; 322:H181-H233. [PMID: 34797172 PMCID: PMC8759964 DOI: 10.1152/ajpheart.00562.2021] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/13/2021] [Revised: 11/16/2021] [Accepted: 11/16/2021] [Indexed: 02/03/2023]
Abstract
Inherited cardiomyopathies are a major cause of mortality and morbidity worldwide and can be caused by mutations in a wide range of proteins located in different cellular compartments. The present review is based on Dr. Ju Chen's 2021 Robert M. Berne Distinguished Lectureship of the American Physiological Society Cardiovascular Section, in which he provided an overview of the current knowledge on the cardiomyopathy-associated proteins that have been studied in his laboratory. The review provides a general summary of the proteins in different compartments of cardiomyocytes associated with cardiomyopathies, with specific focus on the proteins that have been studied in Dr. Chen's laboratory.
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Affiliation(s)
- Marie-Louise Bang
- Institute of Genetic and Biomedical Research (IRGB), National Research Council (CNR), Milan Unit, Milan, Italy
- IRCCS Humanitas Research Hospital, Rozzano (Milan), Italy
| | - Julius Bogomolovas
- Division of Cardiovascular Medicine, Department of Medicine Cardiology, University of California, San Diego, La Jolla, California
| | - Ju Chen
- Division of Cardiovascular Medicine, Department of Medicine Cardiology, University of California, San Diego, La Jolla, California
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5
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Su K, Mayans O, Diederichs K, Fleming JR. Pairwise sequence similarity mapping with PaSiMap: Reclassification of immunoglobulin domains from titin as case study. Comput Struct Biotechnol J 2022; 20:5409-5419. [PMID: 36212532 PMCID: PMC9529554 DOI: 10.1016/j.csbj.2022.09.034] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2022] [Revised: 09/22/2022] [Accepted: 09/22/2022] [Indexed: 11/17/2022] Open
Abstract
A novel multidimensional scaling pipeline for sequence analysis. A simple way to distinguish between unique and shared sequence features. Titin domains were reclassified, improving upon earlier analysis.
Sequence comparison is critical for the functional assignment of newly identified protein genes. As uncharacterized protein sequences accumulate, there is an increasing need for sensitive tools for their classification. Here, we present a novel multidimensional scaling pipeline, PaSiMap, which creates a map of pairwise sequence similarities. Uniquely, PaSiMap distinguishes between unique and shared features, allowing for a distinct view of protein-sequence relationships. We demonstrate PaSiMap’s efficiency in detecting sequence groups and outliers using titin’s 169 immunoglobulin (Ig) domains. We show that Ig domain similarity is hierarchical, being firstly determined by chain location, then by the loop features of the Ig fold and, finally, by super-repeat position. The existence of a previously unidentified domain repeat in the distal, constitutive I-band is revealed. Prototypic Igs, plus notable outliers, are identified and thereby domain classification improved. This re-classification can now guide future molecular research. In summary, we demonstrate that PaSiMap is a sensitive tool for the classification of protein sequences, which adds a new perspective in the understanding of inter-protein relationships. PaSiMap is applicable to any biological system defined by a linear sequence, including polynucleotide chains.
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van der Pijl RJ, Domenighetti AA, Sheikh F, Ehler E, Ottenheijm CAC, Lange S. The titin N2B and N2A regions: biomechanical and metabolic signaling hubs in cross-striated muscles. Biophys Rev 2021; 13:653-677. [PMID: 34745373 PMCID: PMC8553726 DOI: 10.1007/s12551-021-00836-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2021] [Accepted: 08/23/2021] [Indexed: 02/07/2023] Open
Abstract
Muscle specific signaling has been shown to originate from myofilaments and their associated cellular structures, including the sarcomeres, costameres or the cardiac intercalated disc. Two signaling hubs that play important biomechanical roles for cardiac and/or skeletal muscle physiology are the N2B and N2A regions in the giant protein titin. Prominent proteins associated with these regions in titin are chaperones Hsp90 and αB-crystallin, members of the four-and-a-half LIM (FHL) and muscle ankyrin repeat protein (Ankrd) families, as well as thin filament-associated proteins, such as myopalladin. This review highlights biological roles and properties of the titin N2B and N2A regions in health and disease. Special emphasis is placed on functions of Ankrd and FHL proteins as mechanosensors that modulate muscle-specific signaling and muscle growth. This region of the sarcomere also emerged as a hotspot for the modulation of passive muscle mechanics through altered titin phosphorylation and splicing, as well as tethering mechanisms that link titin to the thin filament system.
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Affiliation(s)
| | - Andrea A. Domenighetti
- Shirley Ryan AbilityLab, Chicago, IL USA
- Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago, IL USA
| | - Farah Sheikh
- Division of Cardiology, School of Medicine, UC San Diego, La Jolla, CA USA
| | - Elisabeth Ehler
- Randall Centre for Cell and Molecular Biophysics, School of Cardiovascular Medicine and Sciences, King’s College London, London, UK
| | - Coen A. C. Ottenheijm
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ USA
- Department of Physiology, Amsterdam University Medical Centers, Amsterdam, The Netherlands
| | - Stephan Lange
- Division of Cardiology, School of Medicine, UC San Diego, La Jolla, CA USA
- Department of Molecular and Clinical Medicine, University of Gothenburg, Gothenburg, Sweden
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7
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Kelly C, Gage MJ. Protein Unfolding: Denaturant vs. Force. Biomedicines 2021; 9:biomedicines9101395. [PMID: 34680512 PMCID: PMC8533514 DOI: 10.3390/biomedicines9101395] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Revised: 09/20/2021] [Accepted: 09/28/2021] [Indexed: 11/16/2022] Open
Abstract
While protein refolding has been studied for over 50 years since the pioneering work of Christian Anfinsen, there have been a limited number of studies correlating results between chemical, thermal, and mechanical unfolding. The limited knowledge of the relationship between these processes makes it challenging to compare results between studies if different refolding methods were applied. Our current work compares the energetic barriers and folding rates derived from chemical, thermal, and mechanical experiments using an immunoglobulin-like domain from the muscle protein titin as a model system. This domain, I83, has high solubility and low stability relative to other Ig domains in titin, though its stability can be modulated by calcium. Our experiments demonstrated that the free energy of refolding was equivalent with all three techniques, but the refolding rates exhibited differences, with mechanical refolding having slightly faster rates. This suggests that results from equilibrium-based measurements can be compared directly but care should be given comparing refolding kinetics derived from refolding experiments that used different unfolding methods.
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Affiliation(s)
- Colleen Kelly
- Department of Chemistry, University of Massachusetts Lowell, Lowell, MA 01854, USA;
| | - Matthew J. Gage
- Department of Chemistry, University of Massachusetts Lowell, Lowell, MA 01854, USA;
- UMass Movement Center (UMOVE), University of Massachusetts Lowell, Lowell, MA 01854, USA
- Correspondence:
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8
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Adewale AO, Ahn YH. Titin N2A Domain and Its Interactions at the Sarcomere. Int J Mol Sci 2021; 22:ijms22147563. [PMID: 34299183 PMCID: PMC8305307 DOI: 10.3390/ijms22147563] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Revised: 07/09/2021] [Accepted: 07/12/2021] [Indexed: 12/16/2022] Open
Abstract
Titin is a giant protein in the sarcomere that plays an essential role in muscle contraction with actin and myosin filaments. However, its utility goes beyond mechanical functions, extending to versatile and complex roles in sarcomere organization and maintenance, passive force, mechanosensing, and signaling. Titin’s multiple functions are in part attributed to its large size and modular structures that interact with a myriad of protein partners. Among titin’s domains, the N2A element is one of titin’s unique segments that contributes to titin’s functions in compliance, contraction, structural stability, and signaling via protein–protein interactions with actin filament, chaperones, stress-sensing proteins, and proteases. Considering the significance of N2A, this review highlights structural conformations of N2A, its predisposition for protein–protein interactions, and its multiple interacting protein partners that allow the modulation of titin’s biological effects. Lastly, the nature of N2A for interactions with chaperones and proteases is included, presenting it as an important node that impacts titin’s structural and functional integrity.
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9
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van der Pijl RJ, van den Berg M, van de Locht M, Shen S, Bogaards SJP, Conijn S, Langlais P, Hooijman PE, Labeit S, Heunks LMA, Granzier H, Ottenheijm CAC. Muscle ankyrin repeat protein 1 (MARP1) locks titin to the sarcomeric thin filament and is a passive force regulator. J Gen Physiol 2021; 153:212403. [PMID: 34152365 PMCID: PMC8222902 DOI: 10.1085/jgp.202112925] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2021] [Accepted: 05/19/2021] [Indexed: 12/12/2022] Open
Abstract
Muscle ankyrin repeat protein 1 (MARP1) is frequently up-regulated in stressed muscle, but its effect on skeletal muscle function is poorly understood. Here, we focused on its interaction with the titin–N2A element, found in titin’s molecular spring region. We show that MARP1 binds to F-actin, and that this interaction is stronger when MARP1 forms a complex with titin–N2A. Mechanics and super-resolution microscopy revealed that MARP1 “locks” titin–N2A to the sarcomeric thin filament, causing increased extension of titin’s elastic PEVK element and, importantly, increased passive force. In support of this mechanism, removal of thin filaments abolished the effect of MARP1 on passive force. The clinical relevance of this mechanism was established in diaphragm myofibers of mechanically ventilated rats and of critically ill patients. Thus, MARP1 regulates passive force by locking titin to the thin filament. We propose that in stressed muscle, this mechanism protects the sarcomere from mechanical damage.
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Affiliation(s)
- Robbert J van der Pijl
- Department of Physiology, Amsterdam University Medical Centers, Amsterdam, Netherlands.,Department of Cellular and Molecular Medicine, University of Arizona, Tuscon, AZ
| | - Marloes van den Berg
- Department of Physiology, Amsterdam University Medical Centers, Amsterdam, Netherlands.,Department of Cellular and Molecular Medicine, University of Arizona, Tuscon, AZ
| | - Martijn van de Locht
- Department of Physiology, Amsterdam University Medical Centers, Amsterdam, Netherlands
| | - Shengyi Shen
- Department of Cellular and Molecular Medicine, University of Arizona, Tuscon, AZ
| | - Sylvia J P Bogaards
- Department of Physiology, Amsterdam University Medical Centers, Amsterdam, Netherlands
| | - Stefan Conijn
- Department of Physiology, Amsterdam University Medical Centers, Amsterdam, Netherlands
| | - Paul Langlais
- Division of Endocrinology, University of Arizona, Tucson, AZ
| | - Pleuni E Hooijman
- Department of Physiology, Amsterdam University Medical Centers, Amsterdam, Netherlands
| | - Siegfried Labeit
- Medical Faculty Mannheim, University of Heidelberg, Mannheim, Germany
| | - Leo M A Heunks
- Intensive Care Medicine, Amsterdam University Medical Centers, Amsterdam, Netherlands
| | - Henk Granzier
- Department of Cellular and Molecular Medicine, University of Arizona, Tuscon, AZ
| | - Coen A C Ottenheijm
- Department of Physiology, Amsterdam University Medical Centers, Amsterdam, Netherlands.,Department of Cellular and Molecular Medicine, University of Arizona, Tuscon, AZ
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10
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Zhou T, Fleming JR, Lange S, Hessel AL, Bogomolovas J, Stronczek C, Grundei D, Ghassemian M, Biju A, Börgeson E, Bullard B, Linke WA, Chen J, Kovermann M, Mayans O. Molecular Characterisation of Titin N2A and Its Binding of CARP Reveals a Titin/Actin Cross-linking Mechanism. J Mol Biol 2021; 433:166901. [PMID: 33647290 PMCID: PMC8052292 DOI: 10.1016/j.jmb.2021.166901] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2020] [Revised: 02/14/2021] [Accepted: 02/22/2021] [Indexed: 12/16/2022]
Abstract
Striated muscle responds to mechanical overload by rapidly up-regulating the expression of the cardiac ankyrin repeat protein, CARP, which then targets the sarcomere by binding to titin N2A in the I-band region. To date, the role of this interaction in the stress response of muscle remains poorly understood. Here, we characterise the molecular structure of the CARP-receptor site in titin (UN2A) and its binding of CARP. We find that titin UN2A contains a central three-helix bundle fold (ca 45 residues in length) that is joined to N- and C-terminal flanking immunoglobulin domains by long, flexible linkers with partial helical content. CARP binds titin by engaging an α-hairpin in the three-helix fold of UN2A, the C-terminal linker sequence, and the BC loop in Ig81, which jointly form a broad binding interface. Mutagenesis showed that the CARP/N2A association withstands sequence variations in titin N2A and we use this information to evaluate 85 human single nucleotide variants. In addition, actin co-sedimentation, co-transfection in C2C12 cells, proteomics on heart lysates, and the mechanical response of CARP-soaked myofibrils imply that CARP induces the cross-linking of titin and actin myofilaments, thereby increasing myofibril stiffness. We conclude that CARP acts as a regulator of force output in the sarcomere that preserves muscle mechanical performance upon overload stress.
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Affiliation(s)
- Tiankun Zhou
- Department of Biology, University of Konstanz, 78457 Konstanz, Germany
| | | | - Stephan Lange
- Division of Cardiology, School of Medicine, University of California, San Diego 92093, CA, USA; Wallenberg Laboratory, Department of Molecular and Clinical Medicine, Institute of Medicine, University of Gothenburg, Gothenburg 413 45, Sweden
| | - Anthony L Hessel
- Institute of Physiology II, University Hospital Münster, Münster, Germany
| | - Julius Bogomolovas
- School of Medicine, University of California, San Diego, La Jolla, CA 92093, USA; Department of Cognitive and Clinical Neuroscience, Central Institute of Mental Health, Medical Faculty Mannheim, Heidelberg University, 68159 Mannheim, Germany
| | - Chiara Stronczek
- Department of Biology, University of Konstanz, 78457 Konstanz, Germany
| | - David Grundei
- Department of Biology, University of Konstanz, 78457 Konstanz, Germany
| | - Majid Ghassemian
- Department of Chemistry and Biochemistry, University of California, San Diego 92093, CA, USA
| | - Andrea Biju
- Division of Cardiology, School of Medicine, University of California, San Diego 92093, CA, USA
| | - Emma Börgeson
- Wallenberg Laboratory, Department of Molecular and Clinical Medicine, Institute of Medicine, University of Gothenburg, Gothenburg 413 45, Sweden
| | - Belinda Bullard
- Department of Biology, University of York, York YO10 5DD, UK
| | - Wolfgang A Linke
- Institute of Physiology II, University Hospital Münster, Münster, Germany
| | - Ju Chen
- School of Medicine, University of California, San Diego, La Jolla, CA 92093, USA
| | - Michael Kovermann
- Department of Chemistry, University of Konstanz, 78457 Konstanz, Germany.
| | - Olga Mayans
- Department of Biology, University of Konstanz, 78457 Konstanz, Germany.
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11
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Stronczek C, Lange S, Bullard B, Wolniak S, Börgeson E, Mayans O, Fleming JR. The N2A region of titin has a unique structural configuration. J Gen Physiol 2021; 153:211969. [PMID: 33836065 PMCID: PMC8042602 DOI: 10.1085/jgp.202012766] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Accepted: 03/09/2021] [Indexed: 01/04/2023] Open
Abstract
The N2A segment of titin is a main signaling hub in the sarcomeric I-band that recruits various signaling factors and processing enzymes. It has also been proposed to play a role in force production through its Ca2+-regulated association with actin. However, the molecular basis by which N2A performs these functions selectively within the repetitive and extensive titin chain remains poorly understood. Here, we analyze the structure of N2A components and their association with F-actin. Specifically, we characterized the structure of its Ig domains by elucidating the atomic structure of the I81-I83 tandem using x-ray crystallography and computing a homology model for I80. Structural data revealed these domains to present heterogeneous and divergent Ig folds, where I81 and I83 have unique loop structures. Notably, the I81-I83 tandem has a distinct rotational chain arrangement that confers it a unique multi-domain topography. However, we could not identify specific Ca2+-binding sites in these Ig domains, nor evidence of the association of titin N2A components with F-actin in transfected C2C12 myoblasts or C2C12-derived myotubes. In addition, F-actin cosedimentation assays failed to reveal binding to N2A. We conclude that N2A has a unique architecture that predictably supports its selective recruitment of binding partners in signaling, but that its mechanical role through interaction with F-actin awaits validation.
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Affiliation(s)
- Chiara Stronczek
- Department of Biology, University of Konstanz, Konstanz, Germany
| | - Stephan Lange
- Division of Cardiology, School of Medicine, University of California, San Diego, San Diego, CA.,Wallenberg Laboratory, Department of Molecular and Clinical Medicine, Institute of Medicine, University of Gothenburg, Gothenburg, Sweden
| | | | | | - Emma Börgeson
- Wallenberg Laboratory, Department of Molecular and Clinical Medicine, Institute of Medicine, University of Gothenburg, Gothenburg, Sweden
| | - Olga Mayans
- Department of Biology, University of Konstanz, Konstanz, Germany
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12
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Solution NMR Structure of Titin N2A Region Ig Domain I83 and Its Interaction with Metal Ions. J Mol Biol 2021; 433:166977. [PMID: 33811919 DOI: 10.1016/j.jmb.2021.166977] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2020] [Revised: 03/15/2021] [Accepted: 03/24/2021] [Indexed: 11/21/2022]
Abstract
Titin, the largest single chain protein known so far, has long been known to play a critical role in passive muscle function but recent studies have highlighted titin's role in active muscle function. One of the key elements in this role is the Ca2+-dependent interaction between titin's N2A region and the thin filament. An important element in this interaction is I83, the terminal immunoglobulin domain in the N2A region. There is limited structural information about this domain, but experimental evidence suggests that it plays a critical role in the N2A-actin binding interaction. We now report the solution NMR structure of I83 and characterize its dynamics and metal binding properties in detail. Its structure shows interesting relationships to other I-band Ig domains. Metal binding and dynamics data point towards the way the domain is evolutionarily optimized to interact with neighbouring domains. We also identify a calcium binding site on the N-terminal side of I83, which is expected to impact the interdomain interaction with the I82 domain. Together these results provide a first step towards a better understanding of the physiological effects associated with deletion of most of the I83 domain, as occurs in the mdm mouse model, as well as for future investigations of the N2A region.
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13
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Piroddi N, Pesce P, Scellini B, Manzini S, Ganzetti GS, Badi I, Menegollo M, Cora V, Tiso S, Cinquetti R, Monti L, Chiesa G, Bleyl SB, Busnelli M, Dellera F, Bruno D, Caicci F, Grimaldi A, Taramelli R, Manni L, Sacerdoti D, Tesi C, Poggesi C, Ausoni S, Acquati F, Campione M. Myocardial overexpression of ANKRD1 causes sinus venosus defects and progressive diastolic dysfunction. Cardiovasc Res 2021; 116:1458-1472. [PMID: 31688894 DOI: 10.1093/cvr/cvz291] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Revised: 09/26/2019] [Accepted: 10/30/2019] [Indexed: 12/11/2022] Open
Abstract
AIMS Increased Ankyrin Repeat Domain 1 (ANKRD1) levels linked to gain of function mutations have been associated to total anomalous pulmonary venous return and adult cardiomyopathy occurrence in humans. The link between increased ANKRD1 level and cardiac structural and functional disease is not understood. To get insight into this problem, we have generated a gain of function ANKRD1 mouse model by overexpressing ANKRD1 in the myocardium. METHODS AND RESULTS Ankrd1 is expressed non-homogeneously in the embryonic myocardium, with a dynamic nucleo-sarcomeric localization in developing cardiomyocytes. ANKRD1 transgenic mice present sinus venosus defect, which originates during development by impaired remodelling of early embryonic heart. Adult transgenic hearts develop diastolic dysfunction with preserved ejection fraction, which progressively evolves into heart failure, as shown histologically and haemodynamically. Transgenic cardiomyocyte structure, sarcomeric assembly, and stability are progressively impaired from embryonic to adult life. Postnatal transgenic myofibrils also present characteristic functional alterations: impaired compliance at neonatal stage and impaired lusitropism in adult hearts. Altogether, our combined analyses suggest that impaired embryonic remodelling and adult heart dysfunction in ANKRD1 transgenic mice present a common ground of initial cardiomyocyte defects, which are exacerbated postnatally. Molecular analysis showed transient activation of GATA4-Nkx2.5 transcription in early transgenic embryos and subsequent dynamic transcriptional modulation within titin gene. CONCLUSIONS ANKRD1 is a fine mediator of cardiomyocyte response to haemodynamic load in the developing and adult heart. Increased ANKRD1 levels are sufficient to initiate an altered cellular phenotype, which is progressively exacerbated into a pathological organ response by the high ventricular workload during postnatal life. Our study defines for the first time a unifying picture for ANKRD1 role in heart development and disease and provides the first mechanistic link between ANKRD1 overexpression and cardiac disease onset.
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Affiliation(s)
- Nicoletta Piroddi
- Department of Experimental and Clinical Medicine, University of Florence, 50134 Florence, Italy
| | - Paola Pesce
- Department of Medicine, University of Padua, 35121 Padua, Italy
| | - Beatrice Scellini
- Department of Experimental and Clinical Medicine, University of Florence, 50134 Florence, Italy
| | - Stefano Manzini
- Department of Pharmacological and Biomolecular Sciences, University of Milan, 20133 Milan, Italy
| | - Giulia S Ganzetti
- Department of Pharmacological and Biomolecular Sciences, University of Milan, 20133 Milan, Italy
| | - Ileana Badi
- Department of Biotechnology and Life Sciences, University of Insubria, 21100 Varese, Italy.,Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, UK
| | - Michela Menegollo
- Department of Biomedical Sciences, University of Padua, 35121 Padua, Italy
| | - Virginia Cora
- Department of Biomedical Sciences, University of Padua, 35121 Padua, Italy
| | - Simone Tiso
- Department of Biomedical Sciences, University of Padua, 35121 Padua, Italy
| | - Raffaella Cinquetti
- Department of Biotechnology and Life Sciences, University of Insubria, 21100 Varese, Italy
| | - Laura Monti
- Department of Biotechnology and Life Sciences, University of Insubria, 21100 Varese, Italy
| | - Giulia Chiesa
- Department of Pharmacological and Biomolecular Sciences, University of Milan, 20133 Milan, Italy
| | - Steven B Bleyl
- Department of Pediatrics, University of Utah, Salt Lake City, 84132 UT, USA
| | - Marco Busnelli
- Department of Pharmacological and Biomolecular Sciences, University of Milan, 20133 Milan, Italy
| | - Federica Dellera
- Department of Pharmacological and Biomolecular Sciences, University of Milan, 20133 Milan, Italy
| | - Daniele Bruno
- Department of Biotechnology and Life Sciences, University of Insubria, 21100 Varese, Italy
| | - Federico Caicci
- Department of Biology, University of Padua, 35121 Padua, Italy
| | - Annalisa Grimaldi
- Department of Biotechnology and Life Sciences, University of Insubria, 21100 Varese, Italy
| | - Roberto Taramelli
- Department of Biotechnology and Life Sciences, University of Insubria, 21100 Varese, Italy
| | - Lucia Manni
- Department of Biology, University of Padua, 35121 Padua, Italy
| | - David Sacerdoti
- Department of Medicine, University of Padua, 35121 Padua, Italy
| | - Chiara Tesi
- Department of Experimental and Clinical Medicine, University of Florence, 50134 Florence, Italy
| | - Corrado Poggesi
- Department of Experimental and Clinical Medicine, University of Florence, 50134 Florence, Italy
| | - Simonetta Ausoni
- Department of Biomedical Sciences, University of Padua, 35121 Padua, Italy
| | - Francesco Acquati
- Department of Biotechnology and Life Sciences, University of Insubria, 21100 Varese, Italy
| | - Marina Campione
- Department of Biomedical Sciences, University of Padua, 35121 Padua, Italy.,CNR-Neuroscience Institute, 35121 Padua, Italy
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14
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Sharma S, Subramani S, Popa I. Does protein unfolding play a functional role in vivo? FEBS J 2020; 288:1742-1758. [PMID: 32761965 DOI: 10.1111/febs.15508] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Revised: 07/09/2020] [Accepted: 08/03/2020] [Indexed: 12/21/2022]
Abstract
Unfolding and refolding of multidomain proteins under force have yet to be recognized as a major mechanism of function for proteins in vivo. In this review, we discuss the inherent properties of multidomain proteins under a force vector from a structural and functional perspective. We then characterize three main systems where multidomain proteins could play major roles through mechanical unfolding: muscular contraction, cellular mechanotransduction, and bacterial adhesion. We analyze how key multidomain proteins for each system can produce a gain-of-function from the perspective of a fine-tuned quantized response, a molecular battery, delivery of mechanical work through refolding, elasticity tuning, protection and exposure of cryptic sites, and binding-induced mechanical changes. Understanding how mechanical unfolding and refolding affect function will have important implications in designing mechano-active drugs against conditions such as muscular dystrophy, cancer, or novel antibiotics.
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Affiliation(s)
- Sabita Sharma
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, WI, USA
| | - Smrithika Subramani
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, WI, USA
| | - Ionel Popa
- Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, WI, USA
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15
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N2A Titin: Signaling Hub and Mechanical Switch in Skeletal Muscle. Int J Mol Sci 2020; 21:ijms21113974. [PMID: 32492876 PMCID: PMC7312179 DOI: 10.3390/ijms21113974] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Revised: 05/30/2020] [Accepted: 06/01/2020] [Indexed: 02/06/2023] Open
Abstract
Since its belated discovery, our understanding of the giant protein titin has grown exponentially from its humble beginning as a sarcomeric scaffold to recent recognition of its critical mechanical and signaling functions in active muscle. One uniquely useful model to unravel titin’s functions, muscular dystrophy with myositis (mdm), arose spontaneously in mice as a transposon-like LINE repeat insertion that results in a small deletion in the N2A region of titin. This small deletion profoundly affects hypertrophic signaling and muscle mechanics, thereby providing insights into the function of this specific region and the consequences of its dysfunction. The impact of this mutation is profound, affecting diverse aspects of the phenotype including muscle mechanics, developmental hypertrophy, and thermoregulation. In this review, we explore accumulating evidence that points to the N2A region of titin as a dynamic “switch” that is critical for both mechanical and signaling functions in skeletal muscle. Calcium-dependent binding of N2A titin to actin filaments triggers a cascade of changes in titin that affect mechanical properties such as elastic energy storage and return, as well as hypertrophic signaling. The mdm phenotype also points to the existence of as yet unidentified signaling pathways for muscle hypertrophy and thermoregulation, likely involving titin’s PEVK region as well as the N2A signalosome.
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16
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Lanzicher T, Zhou T, Saripalli C, Keschrumrus V, Smith III JE, Mayans O, Sbaizero O, Granzier H. Single-Molecule Force Spectroscopy on the N2A Element of Titin: Effects of Phosphorylation and CARP. Front Physiol 2020; 11:173. [PMID: 32256378 PMCID: PMC7093598 DOI: 10.3389/fphys.2020.00173] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2019] [Accepted: 02/13/2020] [Indexed: 01/08/2023] Open
Abstract
Titin is a large filamentous protein that forms a sarcomeric myofilament with a molecular spring region that develops force in stretched sarcomeres. The molecular spring has a complex make-up that includes the N2A element. This element largely consists of a 104-residue unique sequence (N2A-Us) flanked by immunoglobulin domains (I80 and I81). The N2A element is of interest because it assembles a signalosome with CARP (Cardiac Ankyrin Repeat Protein) as an important component; CARP both interacts with the N2A-Us and I81 and is highly upregulated in response to mechanical stress. The mechanical properties of the N2A element were studied using single-molecule force spectroscopy, including how these properties are affected by CARP and phosphorylation. Three protein constructs were made that consisted of 0, 1, or 2 N2A-Us elements with flanking I80 and I81 domains and with specific handles at their ends for study by atomic force microscopy (AFM). The N2A-Us behaved as an entropic spring with a persistence length (Lp) of ∼0.35 nm and contour length (Lc) of ∼39 nm. CARP increased the Lp of the N2A-Us and the unfolding force of the Ig domains; force clamp experiments showed that CARP reduced the Ig domain unfolding kinetics. These findings suggest that CARP might function as a molecular chaperone that protects I81 from unfolding when mechanical stress is high. The N2A-Us was found to be a PKA substrate, and phosphorylation was blocked by CARP. Mass spectrometry revealed a PKA phosphosite (Ser-9895 in NP_001254479.2) located at the border between the N2A-Us and I81. AFM studies showed that phosphorylation affected neither the Lp of the N2A-Us nor the Ig domain unfolding force (Funfold). Simulating the force-sarcomere length relation of a single titin molecule containing all spring elements showed that the compliance of the N2A-Us only slightly reduces passive force (1.4%) with an additional small reduction by CARP (0.3%). Thus, it is improbable that the compliance of the N2A element has a mechanical function per se. Instead, it is likely that this compliance has local effects on binding of signaling molecules and that it contributes thereby to strain- and phosphorylation- dependent mechano-signaling.
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Affiliation(s)
- Thomas Lanzicher
- Department of Cellular & Molecular Medicine, The University of Arizona, Tucson, AZ, United States
- Department of Engineering and Architecture, University of Trieste, Trieste, Italy
| | - Tiankun Zhou
- Department of Biology, University of Konstanz, Konstanz, Germany
| | - Chandra Saripalli
- Department of Cellular & Molecular Medicine, The University of Arizona, Tucson, AZ, United States
| | - Vic Keschrumrus
- Department of Cellular & Molecular Medicine, The University of Arizona, Tucson, AZ, United States
| | - John E. Smith III
- Department of Cellular & Molecular Medicine, The University of Arizona, Tucson, AZ, United States
| | - Olga Mayans
- Department of Biology, University of Konstanz, Konstanz, Germany
| | - Orfeo Sbaizero
- Department of Engineering and Architecture, University of Trieste, Trieste, Italy
| | - Henk Granzier
- Department of Cellular & Molecular Medicine, The University of Arizona, Tucson, AZ, United States
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17
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Kelly CM, Manukian S, Kim E, Gage MJ. Differences in stability and calcium sensitivity of the Ig domains in titin's N2A region. Protein Sci 2020; 29:1160-1171. [PMID: 32112607 DOI: 10.1002/pro.3848] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Revised: 02/17/2020] [Accepted: 02/18/2020] [Indexed: 11/11/2022]
Abstract
Titin is a large filamentous protein that spans half a sarcomere, from Z-disk to M-line. The N2A region within the titin molecule exists between the proximal immunoglobulin (Ig) region and the PEVK region and protein-protein interactions involving this region are required for normal muscle function. The N2A region consists of four Ig domains (I80-I83) with a 105 amino acid linker region between I80 and I81 that has a helical nature. Using chemical stability measurements, we show that predicted differences between the adjacent Ig domains (I81-I83) correlate with experimentally determined differences in chemical stability and refolding kinetics. Our work further shows that I83 has the lowest ΔGunfolding , which is increased in the presence of calcium (pCa 4.3), indicating that Ca2+ plays a role in stabilizing this immunoglobulin domain. The characteristics of N2A's three Ig domains provide insight into the stability of the binding sites for proteins that interact with the N2A region. This work also provides insights into how Ca2+ might influence binding events involving N2A.
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Affiliation(s)
- Colleen M Kelly
- Chemistry Department, University of Massachusetts Lowell, Lowell, Massachusetts, USA.,UMass Movement Center, University of Massachusetts Lowell, Lowell, Massachusetts, USA
| | - Sophia Manukian
- Chemistry Department, University of Massachusetts Lowell, Lowell, Massachusetts, USA
| | - Emily Kim
- Chemistry Department, University of Massachusetts Lowell, Lowell, Massachusetts, USA
| | - Matthew J Gage
- Chemistry Department, University of Massachusetts Lowell, Lowell, Massachusetts, USA.,UMass Movement Center, University of Massachusetts Lowell, Lowell, Massachusetts, USA
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18
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Scalable, Non-denaturing Purification of Phosphoproteins Using Ga 3+-IMAC: N2A and M1M2 Titin Components as Study case. Protein J 2019; 38:181-189. [PMID: 30719619 DOI: 10.1007/s10930-019-09815-w] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The purification of phosphorylated proteins in a folded state and in large enough quantity for biochemical or biophysical analysis remains a challenging task. Here, we develop a new implementation of the method of gallium immobilized metal chromatography (Ga3+-IMAC) as to permit the selective enrichment of phosphoproteins in the milligram scale and under native conditions using automated FPLC instrumentation. We apply this method to the purification of the UN2A and M1M2 components of the muscle protein titin upon being monophosphorylated in vitro by cAMP-dependent protein kinase (PKA). We found that UN2A is phosphorylated by PKA at its C-terminus in residue S9578 and M1M2 is phosphorylated in its interdomain linker sequence at position T32607. We demonstrate that the Ga3+-IMAC method is efficient, economical and suitable for implementation in automated purification pipelines for recombinant proteins. The procedure can be applied both to the selective enrichment and to the removal of phosphoproteins from biochemical samples.
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19
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van der Pijl R, Strom J, Conijn S, Lindqvist J, Labeit S, Granzier H, Ottenheijm C. Titin-based mechanosensing modulates muscle hypertrophy. J Cachexia Sarcopenia Muscle 2018; 9:947-961. [PMID: 29978560 PMCID: PMC6204599 DOI: 10.1002/jcsm.12319] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/08/2018] [Revised: 04/30/2018] [Accepted: 05/22/2018] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND Titin is an elastic sarcomeric filament that has been proposed to play a key role in mechanosensing and trophicity of muscle. However, evidence for this proposal is scarce due to the lack of appropriate experimental models to directly test the role of titin in mechanosensing. METHODS We used unilateral diaphragm denervation (UDD) in mice, an in vivo model in which the denervated hemidiaphragm is passively stretched by the contralateral, innervated hemidiaphragm and hypertrophy rapidly occurs. RESULTS In wildtype mice, the denervated hemidiaphragm mass increased 48 ± 3% after 6 days of UDD, due to the addition of both sarcomeres in series and in parallel. To test whether titin stiffness modulates the hypertrophy response, RBM20ΔRRM and TtnΔIAjxn mouse models were used, with decreased and increased titin stiffness, respectively. RBM20ΔRRM mice (reduced stiffness) showed a 20 ± 6% attenuated hypertrophy response, whereas the TtnΔIAjxn mice (increased stiffness) showed an 18 ± 8% exaggerated response after UDD. Thus, muscle hypertrophy scales with titin stiffness. Protein expression analysis revealed that titin-binding proteins implicated previously in muscle trophicity were induced during UDD, MARP1 & 2, FHL1, and MuRF1. CONCLUSIONS Titin functions as a mechanosensor that regulates muscle trophicity.
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Affiliation(s)
- Robbert van der Pijl
- Department of Cellular and Molecular MedicineUniversity of ArizonaTucsonAZUSA
- Dept of PhysiologyVU University Medical CenterAmsterdamThe Netherlands
| | - Joshua Strom
- Department of Cellular and Molecular MedicineUniversity of ArizonaTucsonAZUSA
| | - Stefan Conijn
- Dept of PhysiologyVU University Medical CenterAmsterdamThe Netherlands
| | - Johan Lindqvist
- Department of Cellular and Molecular MedicineUniversity of ArizonaTucsonAZUSA
| | - Siegfried Labeit
- Department of Integrative PathophysiologyMedical Faculty MannheimMannheimGermany
- Myomedix GmbHNeckargemuendGermany
| | - Henk Granzier
- Department of Cellular and Molecular MedicineUniversity of ArizonaTucsonAZUSA
| | - Coen Ottenheijm
- Department of Cellular and Molecular MedicineUniversity of ArizonaTucsonAZUSA
- Dept of PhysiologyVU University Medical CenterAmsterdamThe Netherlands
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20
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Calcium increases titin N2A binding to F-actin and regulated thin filaments. Sci Rep 2018; 8:14575. [PMID: 30275509 PMCID: PMC6167357 DOI: 10.1038/s41598-018-32952-8] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2018] [Accepted: 09/19/2018] [Indexed: 12/30/2022] Open
Abstract
Mutations in titin are responsible for many cardiac and muscle diseases, yet the underlying mechanisms remain largely unexplained. Numerous studies have established roles for titin in muscle function, and Ca2+-dependent interactions between titin and actin have been suggested to play a role in muscle contraction. The present study used co-sedimentation assays, dynamic force spectroscopy (DFS), and in vitro motility (IVM) assays to determine whether the N2A region of titin, overlooked in previous studies, interacts with actin in the presence of Ca2+. Co-sedimentation demonstrated that N2A – F-actin binding increases with increasing protein and Ca2+ concentration, DFS demonstrated increased rupture forces and decreased koff in the presence of Ca2+, and IVM demonstrated a Ca2+-dependent reduction in motility of F-actin and reconstituted thin filaments in the presence of N2A. These results indicate that Ca2+ increases the strength and stability of N2A – actin interactions, supporting the hypothesis that titin plays a regulatory role in muscle contraction. The results further support a model in which N2A – actin binding in active muscle increases titin stiffness, and that impairment of this mechanism contributes to the phenotype in muscular dystrophy with myositis. Future studies are required to determine whether titin – actin binding occurs in skeletal muscle sarcomeres in vivo.
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21
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Tiffany H, Sonkar K, Gage MJ. The insertion sequence of the N2A region of titin exists in an extended structure with helical characteristics. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2016; 1865:1-10. [PMID: 27742555 DOI: 10.1016/j.bbapap.2016.10.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2016] [Revised: 10/05/2016] [Accepted: 10/07/2016] [Indexed: 12/15/2022]
Abstract
The giant sarcomere protein titin is the third filament in muscle and is integral to maintaining sarcomere integrity as well as contributing to both active and passive tension. Titin is a multi-domain protein that contains regions of repeated structural elements. The N2A region sits at the boundary between the proximal Ig region of titin that is extended under low force and the PEVK region that is extended under high force. Multiple binding interactions have been associated with the N2A region and it has been proposed that this region acts as a mechanical stretch sensor. The focus of this work is a 117 amino acid portion of the N2A region (N2A-IS), which resides between the proximal Ig domains and the PEVK region. Our work has shown that the N2A-IS region is predicted to contain helical structure in the center while both termini are predicted to be disordered. Recombinantly expressed N2A-IS protein contains 13% α-helical structure, as measured via circular dichroism. Additional α-helical structure can be induced with 2,2,2-trifluoroethanol, suggesting that there is transient helical structure that might be stabilized in the context of the entire N2A region. The N2A-IS region does not exhibit any cooperativity in either thermal or chemical denaturation studies while size exclusion chromatography and Fluorescence Resonance Energy Transfer demonstrates that the N2A-IS region has an extended structure. Combined, these results lead to a model of the N2A-IS region having a helical core with extended N- and C-termini.
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Affiliation(s)
- Holly Tiffany
- Department of Biology, Northern Arizona University, Flagstaff, AZ, United States
| | - Kanchan Sonkar
- Department of Chemistry and Biochemistry, Northern Arizona University, Flagstaff, AZ, United States
| | - Matthew J Gage
- Department of Chemistry and Biochemistry, Northern Arizona University, Flagstaff, AZ, United States; Center for Bioengineering Innovation, Northern Arizona University, Flagstaff, AZ, United States; Department of Chemistry, University of Massachusetts Lowell, Lowell, MA, United States.
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