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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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2
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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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Nesterenko Y, Hill CJ, Fleming JR, Murray P, Mayans O. The ZT Biopolymer: A Self-Assembling Protein Scaffold for Stem Cell Applications. Int J Mol Sci 2019; 20:E4299. [PMID: 31484291 PMCID: PMC6747707 DOI: 10.3390/ijms20174299] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2019] [Revised: 08/29/2019] [Accepted: 08/30/2019] [Indexed: 12/14/2022] Open
Abstract
The development of cell culture systems for the naturalistic propagation, self-renewal and differentiation of cells ex vivo is a high goal of molecular engineering. Despite significant success in recent years, the high cost of up-scaling cultures, the need for xeno-free culture conditions, and the degree of mimicry of the natural extracellular matrix attainable in vitro using designer substrates continue to pose obstacles to the translation of cell-based technologies. In this regard, the ZT biopolymer is a protein-based, stable, scalable, and economical cell substrate of high promise. ZT is based on the naturally occurring assembly of two human proteins: titin-Z1Z2 and telethonin. These protein building blocks are robust scaffolds that can be conveniently functionalized with full-length proteins and bioactive peptidic motifs by genetic manipulation, prior to self-assembly. The polymer is, thereby, fully encodable. Functionalized versions of the ZT polymer have been shown to successfully sustain the long-term culturing of human embryonic stem cells (hESCs), human induced pluripotent stem cells (hiPSCs), and murine mesenchymal stromal cells (mMSCs). Pluripotency of hESCs and hiPSCs was retained for the longest period assayed (4 months). Results point to the large potential of the ZT system for the creation of a modular, pluri-functional biomaterial for cell-based applications.
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Affiliation(s)
| | - Christopher J Hill
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool L69 3BX, UK
| | | | - Patricia Murray
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool L69 3BX, UK
| | - Olga Mayans
- Department of Biology, University of Konstanz, 78457 Konstanz, Germany.
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4
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Hill CJ, Fleming JR, Mousavinejad M, Nicholson R, Tzokov SB, Bullough PA, Bogomolovas J, Morgan MR, Mayans O, Murray P. Self-Assembling Proteins as High-Performance Substrates for Embryonic Stem Cell Self-Renewal. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2019; 31:e1807521. [PMID: 30866118 DOI: 10.1002/adma.201807521] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2018] [Revised: 01/28/2019] [Indexed: 06/09/2023]
Abstract
The development of extracellular matrix mimetics that imitate niche stem cell microenvironments and support cell growth for technological applications is intensely pursued. Specifically, mimetics are sought that can enact control over the self-renewal and directed differentiation of human pluripotent stem cells (hPSCs) for clinical use. Despite considerable progress in the field, a major impediment to the clinical translation of hPSCs is the difficulty and high cost of large-scale cell production under xeno-free culture conditions using current matrices. Here, a bioactive, recombinant, protein-based polymer, termed ZTFn , is presented that closely mimics human plasma fibronectin and serves as an economical, xeno-free, biodegradable, and functionally adaptable cell substrate. The ZTFn substrate supports with high performance the propagation and long-term self-renewal of human embryonic stem cells while preserving their pluripotency. The ZTFn polymer can, therefore, be proposed as an efficient and affordable replacement for fibronectin in clinical grade cell culturing. Further, it can be postulated that the ZT polymer has significant engineering potential for further orthogonal functionalization in complex cell applications.
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Affiliation(s)
- Christopher J Hill
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Nuffield Building, Crown Street, Liverpool, L69 3BX, UK
- Department of Biochemistry, Institute of Integrative Biology, University of Liverpool, Crown Street, Liverpool, L69 7ZB, UK
| | | | - Masoumeh Mousavinejad
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Nuffield Building, Crown Street, Liverpool, L69 3BX, UK
| | - Rachael Nicholson
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Nuffield Building, Crown Street, Liverpool, L69 3BX, UK
| | - Svetomir B Tzokov
- Department of Molecular Biology and Biotechnology, The Krebs Institute, University of Sheffield, Sheffield, S10 2TN, UK
| | - Per A Bullough
- Department of Molecular Biology and Biotechnology, The Krebs Institute, University of Sheffield, Sheffield, S10 2TN, UK
| | - Julius Bogomolovas
- Department of Medicine, UCSD, La Jolla, CA, 92093, USA
- Department of Cognitive and Clinical Neuroscience, Central Institute of Mental Health, Medical Faculty Mannheim, Heidelberg University, 68159, Mannheim, Germany
| | - Mark R Morgan
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Nuffield Building, Crown Street, Liverpool, L69 3BX, UK
| | - Olga Mayans
- Department of Biochemistry, Institute of Integrative Biology, University of Liverpool, Crown Street, Liverpool, L69 7ZB, UK
- Department of Biology, University of Konstanz, 78457, Konstanz, Germany
| | - Patricia Murray
- Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Nuffield Building, Crown Street, Liverpool, L69 3BX, UK
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5
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Tan H, Su W, Wang P, Zhang W, Sattler M, Zou P. Expression and purification of a difficult sarcomeric protein: Telethonin. Protein Expr Purif 2017; 140:74-80. [DOI: 10.1016/j.pep.2017.08.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2017] [Revised: 08/03/2017] [Accepted: 08/10/2017] [Indexed: 01/21/2023]
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Abstract
Myotilin is a component of the sarcomere where it plays an important role in organisation and maintenance of Z-disk integrity. This involves direct binding to F-actin and filamin C, a function mediated by its Ig domain pair. While the structures of these two individual domains are known, information about their relative orientation and flexibility remains limited. We set on to characterise the Ig domain pair of myotilin with emphasis on its molecular structure, dynamics and phylogeny. First, sequence conservation analysis of myotilin shed light on the molecular basis of myotilinopathies and revealed several motifs in Ig domains found also in I-band proteins. In particular, a highly conserved Glu344 mapping to Ig domain linker, was identified as a critical component of the inter-domain hinge mechanism. Next, SAXS and molecular dynamics revealed that Ig domain pair exists as a multi-conformation species with dynamic exchange between extended and compact orientations. Mutation of AKE motif to AAA further confirmed its impact on inter-domain flexibility. We hypothesise that the conformational plasticity of the Ig domain pair in its unbound form is part of the binding partner recognition mechanism.
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Petoukhov MV, Tuukkanen A. SAS-Based Structural Modelling and Model Validation. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 1009:87-105. [PMID: 29218555 DOI: 10.1007/978-981-10-6038-0_6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Small angle scattering of X-rays (SAXS) and neutrons (SANS) is a structural technique to study disordered systems with chaotic orientations of scattering inhomogeneities at low resolution. An important example of such systems are solutions of biological macromolecules. Rapid development in the methodology for solution scattering data interpretation and model building during the last two decades brought the analysis far beyond the determination of just few overall structural parameters (which was the only possibility in the past) and ensured SAS a firm position in the methods palette of the modern life sciences. The advances in the methodology include ab initio approaches for shape and domain structure restoration from scattering curves without a priori structural knowledge, classification and validation of the models, evaluation of potential ambiguity associated with the reconstruction. In rigid body and hybrid modelling approaches, solution scattering is synergistically used with other structural techniques utilizing the complementary information such as atomic models of the components, intramolecular contacts, subunits orientations etc. for the reconstruction of complex systems. The usual requirement of the sample monodispersity has been loosed recently and the technique can now address such systems as weakly bound oligomers and transient complexes. These state-of-the-art methods are described together with the examples of their applications and the possible ways of post-processing of the models.
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Affiliation(s)
- Maxim V Petoukhov
- Hamburg Unit, European Molecular Biology Laboratory, EMBL c/o DESY, Notkestrasse 85, 22607, Hamburg, Germany. .,Federal Scientific Research Centre "Crystallography and Photonics", RAS, Leninsky prospect 59, 119333, Moscow, Russia. .,A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, RAS, Leninsky prospect 31, 119071, Moscow, Russia.
| | - Anne Tuukkanen
- Hamburg Unit, European Molecular Biology Laboratory, EMBL c/o DESY, Notkestrasse 85, 22607, Hamburg, Germany
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8
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Structural advances on titin: towards an atomic understanding of multi-domain functions in myofilament mechanics and scaffolding. Biochem Soc Trans 2016; 43:850-5. [PMID: 26517893 DOI: 10.1042/bst20150084] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Titin is a gigantic filamentous protein of the muscle sarcomere that plays roles in myofibril mechanics and homoeostasis. 3D-structures of multi-domain fragments of titin are now available that start revealing the molecular mechanisms governing its mechanical and scaffolding functions. This knowledge is now being translated into the fabrication of self-assembling biopolymers. Here we review the structural advances on titin, the novel concepts derived from these and the emerging translational avenues.
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9
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Konarev PV, Petoukhov MV, Svergun DI. Rapid automated superposition of shapes and macromolecular models using spherical harmonics. J Appl Crystallogr 2016; 49:953-960. [PMID: 27275142 PMCID: PMC4886985 DOI: 10.1107/s1600576716005793] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2016] [Accepted: 04/07/2016] [Indexed: 01/20/2023] Open
Abstract
A rapid algorithm to superimpose macromolecular models in Fourier space is proposed and implemented (SUPALM). The method uses a normalized integrated cross-term of the scattering amplitudes as a proximity measure between two three-dimensional objects. The reciprocal-space algorithm allows for direct matching of heterogeneous objects including high- and low-resolution models represented by atomic coordinates, beads or dummy residue chains as well as electron microscopy density maps and inhomogeneous multi-phase models (e.g. of protein-nucleic acid complexes). Using spherical harmonics for the computation of the amplitudes, the method is up to an order of magnitude faster than the real-space algorithm implemented in SUPCOMB by Kozin & Svergun [J. Appl. Cryst. (2001 ▸), 34, 33-41]. The utility of the new method is demonstrated in a number of test cases and compared with the results of SUPCOMB. The spherical harmonics algorithm is best suited for low-resolution shape models, e.g. those provided by solution scattering experiments, but also facilitates a rapid cross-validation against structural models obtained by other methods.
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Affiliation(s)
- Petr V. Konarev
- Laboratory of Reflectometry and Small-Angle Scattering, A.V. Shubnikov Institute of Crystallography of Federal Scientific Research Centre ‘Crystallography and Photonics’, Russian Academy of Sciences, Leninsky prospekt 59, Moscow, 119333, Russian Federation
| | - Maxim V. Petoukhov
- Hamburg Outstation, European Molecular Biology Laboratory, Notkestrasse 85, Hamburg, 22607, Germany
| | - Dmitri I. Svergun
- Hamburg Outstation, European Molecular Biology Laboratory, Notkestrasse 85, Hamburg, 22607, Germany
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10
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Bodmer NK, Theisen KE, Dima RI. Molecular investigations into the mechanics of a muscle anchoring complex. Biophys J 2016; 108:2322-32. [PMID: 25954889 DOI: 10.1016/j.bpj.2015.03.036] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Revised: 02/16/2015] [Accepted: 03/13/2015] [Indexed: 11/15/2022] Open
Abstract
The titin-telethonin complex, essential for anchoring filaments in the Z-disk of the sarcomere, is composed of immunoglobulin domains. Surprisingly, atomic force microscopy experiments showed that it resists forces much higher than the typical immunoglobulin domain and that the force distribution is unusually broad. To investigate the origin of this behavior, we developed a multiscale simulation approach, combining minimalist and atomistic models (SOP-AT). By following the mechanical response of the complex on experimental timescales, we found that the mechanical stability of titin-telethonin is modulated primarily by the strength of contacts between telethonin and the two titin chains, and secondarily by the timescales of conformational excursions inside telethonin and the pulled titin domains. Importantly, the conformational transitions executed by telethonin in simulations support its proposed role in mechanosensing. Our SOP-AT computational approach thus provides a powerful tool for the exploration of the link between conformational diversity and the broadness of the mechanical response, which can be applied to other multidomain complexes.
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Affiliation(s)
| | - Kelly E Theisen
- Department of Chemistry, University of Cincinnati, Cincinnati, Ohio
| | - Ruxandra I Dima
- Department of Chemistry, University of Cincinnati, Cincinnati, Ohio.
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11
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Göbl C, Madl T, Simon B, Sattler M. NMR approaches for structural analysis of multidomain proteins and complexes in solution. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2014; 80:26-63. [PMID: 24924266 DOI: 10.1016/j.pnmrs.2014.05.003] [Citation(s) in RCA: 130] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Accepted: 05/14/2014] [Indexed: 05/22/2023]
Abstract
NMR spectroscopy is a key method for studying the structure and dynamics of (large) multidomain proteins and complexes in solution. It plays a unique role in integrated structural biology approaches as especially information about conformational dynamics can be readily obtained at residue resolution. Here, we review NMR techniques for such studies focusing on state-of-the-art tools and practical aspects. An efficient approach for determining the quaternary structure of multidomain complexes starts from the structures of individual domains or subunits. The arrangement of the domains/subunits within the complex is then defined based on NMR measurements that provide information about the domain interfaces combined with (long-range) distance and orientational restraints. Aspects discussed include sample preparation, specific isotope labeling and spin labeling; determination of binding interfaces and domain/subunit arrangements from chemical shift perturbations (CSP), nuclear Overhauser effects (NOEs), isotope editing/filtering, cross-saturation, and differential line broadening; and based on paramagnetic relaxation enhancements (PRE) using covalent and soluble spin labels. Finally, the utility of complementary methods such as small-angle X-ray or neutron scattering (SAXS, SANS), electron paramagnetic resonance (EPR) or fluorescence spectroscopy techniques is discussed. The applications of NMR techniques are illustrated with studies of challenging (high molecular weight) protein complexes.
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Affiliation(s)
- Christoph Göbl
- Biomolecular NMR and Center for Integrated Protein Science Munich at Department Chemie, Technische Universität München, Garching, Germany
| | - Tobias Madl
- Biomolecular NMR and Center for Integrated Protein Science Munich at Department Chemie, Technische Universität München, Garching, Germany; Institute of Structural Biology, Helmholtz Zentrum München, Neuherberg, Germany; Institute of Molecular Biology, University of Graz, Graz, Austria.
| | - Bernd Simon
- European Molecular Biology Laboratory, Structural and Computational Biology Unit, Meyerhofstraße 1, 69117 Heidelberg, Germany
| | - Michael Sattler
- Biomolecular NMR and Center for Integrated Protein Science Munich at Department Chemie, Technische Universität München, Garching, Germany; Institute of Structural Biology, Helmholtz Zentrum München, Neuherberg, Germany.
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12
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Abstract
Giant muscle proteins (e.g., titin, nebulin, and obscurin) play a seminal role in muscle elasticity, stretch response, and sarcomeric organization. Each giant protein consists of multiple tandem structural domains, usually arranged in a modular fashion spanning 500 kDa to 4 MDa. Although many of the domains are similar in structure, subtle differences create a unique function of each domain. Recent high and low resolution structural and dynamic studies now suggest more nuanced overall protein structures than previously realized. These findings show that atomic structure, interactions between tandem domains, and intrasarcomeric environment all influence the shape, motion, and therefore function of giant proteins. In this article we will review the current understanding of titin, obscurin, and nebulin structure, from the atomic level through the molecular level.
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Affiliation(s)
- Logan C Meyer
- Department of Chemistry and Biochemistry, James Madison University Harrisonburg, VA, USA
| | - Nathan T Wright
- Department of Chemistry and Biochemistry, James Madison University Harrisonburg, VA, USA
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13
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Petoukhov MV, Svergun DI. Applications of small-angle X-ray scattering to biomacromolecular solutions. Int J Biochem Cell Biol 2012; 45:429-37. [PMID: 23142499 DOI: 10.1016/j.biocel.2012.10.017] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2012] [Revised: 10/25/2012] [Accepted: 10/30/2012] [Indexed: 01/10/2023]
Abstract
Small-angle scattering of X-rays (SAXS) is an established method for low-resolution structural characterization of biological macromolecules in solution. Being complementary to the high resolution methods (X-ray crystallography and NMR), SAXS is often used in combination with them. The technique provides overall three-dimensional structures using ab initio reconstructions and hybrid modeling, and allows one to quantitatively characterize equilibrium mixtures as well as flexible systems. Recent progress in SAXS instrumentation, most notably, high brilliance synchrotron sources, has paved the way for high throughput automated SAXS studies allowing screening of external conditions (pH, temperature, ligand binding etc.). The modern approaches for SAXS data analysis are presented in this review including rapid characterization of macromolecular solutions in terms of low-resolution shapes, validation of high-resolution models in close-to-native conditions, quaternary structure analysis of complexes and quantitative description of the oligomeric composition in mixtures. Practical aspects of SAXS as a standalone tool and its combinations with other structural, biophysical or bioinformatics methods are reviewed. The capabilities of the technique are illustrated by a selection of recent applications for the studies of biological molecules. Future perspectives on SAXS and its potential impact to structural molecular biology are discussed.
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Affiliation(s)
- Maxim V Petoukhov
- European Molecular Biology Laboratory, Hamburg Outstation, Notkestrasse 85, 22607 Hamburg, Germany
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14
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Garcia-Manyes S, Badilla CL, Alegre-Cebollada J, Javadi Y, Fernández JM. Spontaneous dimerization of titin protein Z1Z2 domains induces strong nanomechanical anchoring. J Biol Chem 2012; 287:20240-7. [PMID: 22523089 DOI: 10.1074/jbc.m112.355883] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Muscle elasticity strongly relies on the mechanical anchoring of the giant protein titin to both the sarcomere M-band and the Z-disk. Such strong attachment ensures the reversible dynamics of the stretching-relaxing cycles determining the muscle passive elasticity. Similarly, the design of biomaterials with enhanced elastic function requires experimental strategies able to secure the constituent molecules to avoid mechanical failure. Here we show that an engineered titin-mimicking protein is able to spontaneously dimerize in solution. Our observations reveal that the titin Z1Z2 domains are key to induce dimerization over a long-range distance in proteins that would otherwise remain in their monomeric form. Using single molecule force spectroscopy, we measure the threshold force that triggers the noncovalent transition from protein dimer to monomer, occurring at ∼700 piconewtons. Such extremely high mechanical stability is likely to be a natural protective mechanism that guarantees muscle integrity. We propose a simple molecular model to understand the force-induced dimer-to-monomer transition based on the geometric distribution of forces occurring within a dimeric protein under mechanical tension.
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Affiliation(s)
- Sergi Garcia-Manyes
- Department of Physics and Randall Division of Cell and Molecular Biophysics, King's College London, London WC2R 2LS, United Kingdom.
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15
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Bruning M, Barsukov I, Franke B, Barbieri S, Volk M, Leopoldseder S, Ucurum Z, Mayans O. The intracellular Ig fold: a robust protein scaffold for the engineering of molecular recognition. Protein Eng Des Sel 2012; 25:205-12. [PMID: 22355150 DOI: 10.1093/protein/gzs007] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Protein scaffolds that support molecular recognition have multiple applications in biotechnology. Thus, protein frames with robust structural cores but adaptable surface loops are in continued demand. Recently, notable progress has been made in the characterization of Ig domains of intracellular origin--in particular, modular components of the titin myofilament. These Ig belong to the I(intermediate)-type, are remarkably stable, highly soluble and undemanding to produce in the cytoplasm of Escherichia coli. Using the Z1 domain from titin as representative, we show that the I-Ig fold tolerates the drastic diversification of its CD loop, constituting an effective peptide display system. We examine the stability of CD-loop-grafted Z1-peptide chimeras using differential scanning fluorimetry, Fourier transform infrared spectroscopy and nuclear magnetic resonance and demonstrate that the introduction of bioreactive affinity binders in this position does not compromise the structural integrity of the domain. Further, the binding efficiency of the exogenous peptide sequences in Z1 is analyzed using pull-down assays and isothermal titration calorimetry. We show that an internally grafted, affinity FLAG tag is functional within the context of the fold, interacting with the anti-FLAG M2 antibody in solution and in affinity gel. Together, these data reveal the potential of the intracellular Ig scaffold for targeted functionalization.
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Affiliation(s)
- Marc Bruning
- Institute of Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, UK
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16
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A simple procedure to evaluate the efficiency of bio-macromolecular rigid-body refinement by small-angle scattering. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2011; 41:1-11. [DOI: 10.1007/s00249-011-0751-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2011] [Accepted: 09/06/2011] [Indexed: 02/02/2023]
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17
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Chami M, Franke B, Mayans O, Kreplak L. Assembly of a protein “brush” by end-grafting titin fragments to liposomes. J Biosci Bioeng 2011; 112:178-9. [DOI: 10.1016/j.jbiosc.2011.04.014] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2011] [Revised: 04/21/2011] [Accepted: 04/28/2011] [Indexed: 10/18/2022]
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18
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Hsin J, Strümpfer J, Lee EH, Schulten K. Molecular Origin of the Hierarchical Elasticity of Titin: Simulation, Experiment, and Theory. Annu Rev Biophys 2011; 40:187-203. [DOI: 10.1146/annurev-biophys-072110-125325] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Jen Hsin
- Department of Physics, Urbana, Illinois 61801
- Beckman Institute for Advanced Science and Technology, Urbana, Illinois 61801
| | - Johan Strümpfer
- Department of Physics, Urbana, Illinois 61801
- Center for Biophysics and Computational Biology, Urbana, Illinois 61801
| | - Eric H. Lee
- Beckman Institute for Advanced Science and Technology, Urbana, Illinois 61801
- Center for Biophysics and Computational Biology, Urbana, Illinois 61801
- College of Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801;
| | - Klaus Schulten
- Department of Physics, Urbana, Illinois 61801
- Beckman Institute for Advanced Science and Technology, Urbana, Illinois 61801
- Center for Biophysics and Computational Biology, Urbana, Illinois 61801
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19
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Krüger M, Linke WA. The giant protein titin: a regulatory node that integrates myocyte signaling pathways. J Biol Chem 2011; 286:9905-12. [PMID: 21257761 DOI: 10.1074/jbc.r110.173260] [Citation(s) in RCA: 116] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Titin, the largest protein in the human body, is well known as a molecular spring in muscle cells and scaffold protein aiding myofibrillar assembly. However, recent evidence has established another important role for titin: that of a regulatory node integrating, and perhaps coordinating, diverse signaling pathways, particularly in cardiomyocytes. We review key findings within this emerging field, including those related to phosphorylation of the titin springs, and also discuss how titin participates in hypertrophic gene regulation and protein quality control.
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Affiliation(s)
- Martina Krüger
- Department of Cardiovascular Physiology, Ruhr University Bochum, D-44780 Bochum, Germany.
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Madl T, Gabel F, Sattler M. NMR and small-angle scattering-based structural analysis of protein complexes in solution. J Struct Biol 2010; 173:472-82. [PMID: 21074620 DOI: 10.1016/j.jsb.2010.11.004] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2010] [Revised: 11/01/2010] [Accepted: 11/04/2010] [Indexed: 01/14/2023]
Abstract
Structural analysis of multi-domain protein complexes is a key challenge in current biology and a prerequisite for understanding the molecular basis of essential cellular processes. The use of solution techniques is important for characterizing the quaternary arrangements and dynamics of domains and subunits of these complexes. In this respect solution NMR is the only technique that allows atomic- or residue-resolution structure determination and investigation of dynamic properties of multi-domain proteins and their complexes. As experimental NMR data for large protein complexes are sparse, it is advantageous to combine these data with additional information from other solution techniques. Here, the utility and computational approaches of combining solution state NMR with small-angle X-ray and Neutron scattering (SAXS/SANS) experiments for structural analysis of large protein complexes is reviewed. Recent progress in experimental and computational approaches of combining NMR and SAS are discussed and illustrated with recent examples from the literature. The complementary aspects of combining NMR and SAS data for studying multi-domain proteins, i.e. where weakly interacting domains are connected by flexible linkers, are illustrated with the structural analysis of the tandem RNA recognition motif (RRM) domains (RRM1-RRM2) of the human splicing factor U2AF65 bound to a nine-uridine (U9) RNA oligonucleotide.
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Affiliation(s)
- Tobias Madl
- Institute of Structural Biology, Helmholtz Zentrum München, Ingolstädter Landstr. 1, 85764 Neuherberg, Germany
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21
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Bruning M, Kreplak L, Leopoldseder S, Müller SA, Ringler P, Duchesne L, Fernig DG, Engel A, Ucurum-Fotiadis Z, Mayans O. Bipartite design of a self-fibrillating protein copolymer with nanopatterned peptide display capabilities. NANO LETTERS 2010; 10:4533-4537. [PMID: 20954695 DOI: 10.1021/nl1024886] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The development of biomatrices for technological and biomedical applications employs self-assembled scaffolds built from short peptidic motifs. However, biopolymers composed of protein domains would offer more varied molecular frames to introduce finer and more complex functionalities in bioreactive scaffolds using bottom-up approaches. Yet, the rules governing the three-dimensional organization of protein architectures in nature are complex and poorly understood. As a result, the synthetic fabrication of ordered protein association into polymers poses major challenges to bioengineering. We have now fabricated a self-assembling protein nanofiber with predictable morphologies and amenable to bottom-up customization, where features supporting function and assembly are spatially segregated. The design was inspired by the cross-linking of titin filaments by telethonin in the muscle sarcomere. The resulting fiber is a two-protein system that has nanopatterned peptide display capabilities as shown by the recruitment of functionalized gold nanoparticles at regular intervals of ∼ 5 nm, yielding a semiregular linear array over micrometers. This polymer promises the uncomplicated display of biologically active motifs to selectively bind and organize matter in the fine nanoscale. Further, its conceptual design has high potential for controlled plurifunctionalization.
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Affiliation(s)
- Marc Bruning
- Division of Structural Biology, Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
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22
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Bucher RM, Svergun DI, Muhle-Goll C, Mayans O. The Structure of the FnIII Tandem A77-A78 Points to a Periodically Conserved Architecture in the Myosin-Binding Region of Titin. J Mol Biol 2010; 401:843-53. [DOI: 10.1016/j.jmb.2010.06.011] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2010] [Revised: 06/01/2010] [Accepted: 06/05/2010] [Indexed: 11/25/2022]
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23
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Roles of titin in the structure and elasticity of the sarcomere. J Biomed Biotechnol 2010; 2010:612482. [PMID: 20625501 PMCID: PMC2896707 DOI: 10.1155/2010/612482] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2010] [Accepted: 05/13/2010] [Indexed: 11/18/2022] Open
Abstract
The giant protein titin is thought to play major roles in the assembly and function of muscle sarcomeres. Structural details, such as widths of Z- and M-lines and periodicities in the thick filaments, correlate with the substructure in the respective regions of the titin molecule. Sarcomere rest length, its operating range of lengths, and passive elastic properties are also directly controlled by the properties of titin. Here we review some recent titin data and discuss its implications for sarcomere architecture and elasticity.
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24
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Dynamic strength of titin's Z-disk end. J Biomed Biotechnol 2010; 2010:838530. [PMID: 20414364 PMCID: PMC2857871 DOI: 10.1155/2010/838530] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2009] [Accepted: 02/11/2010] [Indexed: 11/17/2022] Open
Abstract
Titin is a giant filamentous protein traversing the half sarcomere of striated muscle with putative functions as diverse as providing structural template, generating elastic response, and sensing and relaying mechanical information. The Z-disk region of titin, which corresponds to the N-terminal end of the molecule, has been thought to be a hot spot for mechanosensing while also serving as anchorage for its sarcomeric attachment. Understanding the mechanics of titin's Z-disk region, particularly under the effect of binding proteins, is of great interest. Here we briefly review recent findings on the structure, molecular associations, and mechanics of titin's Z-disk region. In addition, we report experimental results on the dynamic strength of titin's Z1Z2 domains measured by nanomechanical manipulation of the chemical dimer of a recombinant protein fragment.
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25
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Shape and flexibility in the titin 11-domain super-repeat. J Mol Biol 2010; 397:1092-105. [PMID: 20138893 DOI: 10.1016/j.jmb.2010.01.073] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2009] [Revised: 01/28/2010] [Accepted: 01/29/2010] [Indexed: 11/24/2022]
Abstract
Titin is a giant protein of striated muscle with important roles in the assembly, intracellular signalling and passive mechanical properties of sarcomeres. The molecule consists principally of approximately 300 immunoglobulin and fibronectin domains arranged in a chain more than 1 mum long. The isoform-dependent N-terminal part of the molecule forms an elastic connection between the end of the thick filament and the Z-line. The larger, constitutively expressed C-terminal part is bound to the thick filament. Through most of the thick filament part, the immunoglobulin and fibronectin domains are arranged in a repeating pattern of 11 domains termed the 'large super-repeat'. There are 11 contiguous copies of the large super-repeat making up a segment of the molecule nearly 0.5 mum long. We have studied a set of two-domain and three-domain recombinant fragments from the large super-repeat region by electron microscopy, synchrotron X-ray solution scattering and analytical ultracentrifugation, with the goal of reconstructing the overall structure of this part of titin. The data illustrate different average conformations in different domain pairs, which correlate with differences in interdomain linker lengths. They also illustrate interdomain bending and flexibility around average conformations. Overall, the data favour a helical conformation in the super-repeat. They also suggest that this region of titin is dimerized when bound to the thick filament.
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26
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Effect of interdomain dynamics on the structure determination of modular proteins by small-angle scattering. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2009; 39:769-80. [DOI: 10.1007/s00249-009-0549-3] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2009] [Revised: 09/10/2009] [Accepted: 09/24/2009] [Indexed: 01/08/2023]
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Pinotsis N, Abrusci P, Djinović-Carugo K, Wilmanns M. Terminal assembly of sarcomeric filaments by intermolecular beta-sheet formation. Trends Biochem Sci 2008; 34:33-9. [PMID: 18996015 DOI: 10.1016/j.tibs.2008.09.009] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2008] [Revised: 09/21/2008] [Accepted: 09/22/2008] [Indexed: 11/28/2022]
Abstract
The contraction-relaxation cycle of muscle cells translates into large movements of several filament systems in sarcomeres, requiring special molecular mechanisms to maintain their structural integrity. Recent structural and functional data from three filaments harboring extensive arrays of immunoglobulin-like domains - titin, filamin and myomesin--have, for the first time, unraveled a common function of their terminal domains: assembly and anchoring of the respective filaments. In each case, the protein-protein interactions are mediated by antiparallel dimerization modules via intermolecular beta-sheets. These observations on terminal filament assembly indicate an attractive model for several other filament proteins that require structural characterization.
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Affiliation(s)
- Nikos Pinotsis
- European Molecular Biology Laboratory Hamburg, Hamburg, Germany
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28
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Gabel F, Simon B, Nilges M, Petoukhov M, Svergun D, Sattler M. A structure refinement protocol combining NMR residual dipolar couplings and small angle scattering restraints. JOURNAL OF BIOMOLECULAR NMR 2008; 41:199-208. [PMID: 18670889 DOI: 10.1007/s10858-008-9258-y] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2008] [Accepted: 05/16/2008] [Indexed: 05/26/2023]
Abstract
We present the implementation of a target function based on Small Angle Scattering data (Gabel et al. Eur Biophys J 35(4):313-327, 2006) into the Crystallography and NMR Systems (CNS) and demonstrate its utility in NMR structure calculations by simultaneous application of small angle scattering (SAS) and residual dipolar coupling (RDC) restraints. The efficiency and stability of the approach are demonstrated by reconstructing the structure of a two domain region of the 31 kDa nuclear export factor TAP (TIP-associated protein). Starting with the high resolution X-ray structures of the two individual TAP domains, the translational and orientational domain arrangement is refined simultaneously. We tested the stability of the protocol against variations of the SAS target parameters and the number of RDCs and their uncertainties. The activation of SAS restraints results in an improved translational clustering of the domain positions and lifts part of the fourfold degeneracy of their orientations (associated with a single alignment tensor). The resulting ensemble of structures reflects the conformational space that is consistent with the experimental SAS and RDC data. The SAS target function is computationally very efficient. SAS restraints can be activated at different levels of precision and only a limited SAS angular range is required. When combined with additional data from chemical shift perturbation, paramagnetic relaxation enhancement or mutational analysis the SAS refinement is an efficient approach for defining the topology of multi-domain and/or multimeric biomolecular complexes in solution based on available high resolution structures (NMR or X-ray) of the individual domains.
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Affiliation(s)
- F Gabel
- Structural and Computational Biology Unit, EMBL, Meyerhofstrasse 1, Heidelberg, Germany
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29
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Bertini I, Calderone V, Fragai M, Jaiswal R, Luchinat C, Melikian M, Mylonas E, Svergun DI. Evidence of reciprocal reorientation of the catalytic and hemopexin-like domains of full-length MMP-12. J Am Chem Soc 2008; 130:7011-21. [PMID: 18465858 DOI: 10.1021/ja710491y] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The proteolytic activity of matrix metalloproteinases toward extracellular matrix components (ECM), cytokines, chemokines, and membrane receptors is crucial for several homeostatic and pathological processes. Active MMPs are a family of single-chain enzymes (23 family members in the human genome), most of which constituted by a catalytic domain and by a hemopexin-like domain connected by a linker. The X-ray structures of MMP-1 and MMP-2 suggest a conserved and well-defined spatial relationship between the two domains. Here we present structural data for MMP-12, suitably stabilized against self-hydrolysis, both in solution (NMR and SAXS) and in the solid state (X-ray), showing that the hemopexin-like and the catalytic domains experience conformational freedom with respect to each other on a time scale shorter than 10(-8) s. Hints on the probable conformations are also obtained. This experimental finding opens new perspectives for the often hypothesized active role of the hemopexin-like domain in the enzymatic activity of MMPs.
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Affiliation(s)
- Ivano Bertini
- Magnetic Resonance Center (CERM), University of Florence, Via L. Sacconi 6, 50019 Sesto Fiorentino, Italy.
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30
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X-ray solution scattering (SAXS) combined with crystallography and computation: defining accurate macromolecular structures, conformations and assemblies in solution. Q Rev Biophys 2008; 40:191-285. [PMID: 18078545 DOI: 10.1017/s0033583507004635] [Citation(s) in RCA: 845] [Impact Index Per Article: 52.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Crystallography supplies unparalleled detail on structural information critical for mechanistic analyses; however, it is restricted to describing low energy conformations of macromolecules within crystal lattices. Small angle X-ray scattering (SAXS) offers complementary information about macromolecular folding, unfolding, aggregation, extended conformations, flexibly linked domains, shape, conformation, and assembly state in solution, albeit at the lower resolution range of about 50 A to 10 A resolution, but without the size limitations inherent in NMR and electron microscopy studies. Together these techniques can allow multi-scale modeling to create complete and accurate images of macromolecules for modeling allosteric mechanisms, supramolecular complexes, and dynamic molecular machines acting in diverse processes ranging from eukaryotic DNA replication, recombination and repair to microbial membrane secretion and assembly systems. This review addresses both theoretical and practical concepts, concerns and considerations for using these techniques in conjunction with computational methods to productively combine solution scattering data with high-resolution structures. Detailed aspects of SAXS experimental results are considered with a focus on data interpretation tools suitable to model protein and nucleic acid macromolecular structures, including membrane protein, RNA, DNA, and protein-nucleic acid complexes. The methods discussed provide the basis to examine molecular interactions in solution and to study macromolecular flexibility and conformational changes that have become increasingly relevant for accurate understanding, simulation, and prediction of mechanisms in structural cell biology and nanotechnology.
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Abstract
Modular proteins such as titin, fibronectin, and cadherin are ubiquitous components of living cells. Often involved in signaling and mechanical processes, their architecture is characterized by domains containing a variable number of heterogeneous "repeats" arranged in series, with either flexible or rigid linker regions that determine their elasticity. Cadherin repeats arranged in series are unique in that linker regions also feature calcium-binding motifs. While it is well known that the extracellular repeats of cadherin proteins mediate cell-cell adhesion in a calcium-dependent manner, the molecular mechanisms behind the influence of calcium in adhesion dynamics and cadherin's mechanical response are not well understood. Here we show, using molecular dynamics simulations, how calcium ions control the structural integrity of cadherin's linker regions, thereby affecting cadherin's equilibrium dynamics, the availability of key residues involved in cell-cell adhesion, and cadherin's mechanical response. The all-atom, multi-nanosecond molecular dynamics simulations involved the entire C-cadherin extracellular domain solvated in water (a 345,000 atom system). Equilibrium simulations show that the extracellular domain maintains its crystal conformation (elongated and slightly curved) when calcium ions are present. In the absence of calcium ions, however, it assumes a disordered conformation. The conserved residue Trp(2), which is thought to insert itself into a hydrophobic pocket of another cadherin molecule (thereby providing the basis for cell-cell adhesion), switches conformation from exposed to intermittently buried upon removal of calcium ions. Furthermore, the overall mechanical response of C-cadherin's extracellular domain is characterized at low force by changes in shape (tertiary structure elasticity), and at high force by unraveling of secondary structure elements (secondary structure elasticity). This mechanical response is modulated by calcium ions at both low and high force, switching from a stiff, rod-like to a soft, spring-like behavior upon removal of ions. The simulations provide an unprecedented molecular view of calcium-mediated allostery in cadherins, also illustrating the general principles of linker-mediated elasticity of modular proteins relevant not only for cell-cell adhesion and sound transduction, but also muscle elasticity.
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32
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Grishaev A, Tugarinov V, Kay LE, Trewhella J, Bax A. Refined solution structure of the 82-kDa enzyme malate synthase G from joint NMR and synchrotron SAXS restraints. JOURNAL OF BIOMOLECULAR NMR 2008; 40:95-106. [PMID: 18008171 DOI: 10.1007/s10858-007-9211-5] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2007] [Revised: 10/30/2007] [Accepted: 11/02/2007] [Indexed: 05/25/2023]
Abstract
Determination of the accurate three-dimensional structure of large proteins by NMR remains challenging due to a loss in the density of experimental restraints resulting from the often prerequisite perdeuteration. Solution small-angle scattering, which carries long-range translational information, presents an opportunity to enhance the structural accuracy of derived models when used in combination with global orientational NMR restraints such as residual dipolar couplings (RDCs) and residual chemical shift anisotropies (RCSAs). We have quantified the improvements in accuracy that can be obtained using this strategy for the 82 kDa enzyme Malate Synthase G (MSG), currently the largest single chain protein solved by solution NMR. Joint refinement against NMR and scattering data leads to an improvement in structural accuracy as evidenced by a decrease from approximately 4.5 to approximately 3.3 A of the backbone rmsd between the derived model and the high-resolution X-ray structure, PDB code 1D8C. This improvement results primarily from medium-angle scattering data, which encode the overall molecular shape, rather than the lowest angle data that principally determine the radius of gyration and the maximum particle dimension. The effect of the higher angle data, which are dominated by internal density fluctuations, while beneficial, is also found to be relatively small. Our results demonstrate that joint NMR/SAXS refinement can yield significantly improved accuracy in solution structure determination and will be especially well suited for the study of systems with limited NMR restraints such as large proteins, oligonucleotides, or their complexes.
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Affiliation(s)
- Alexander Grishaev
- Laboratory of Chemical Physics, NIDDK, National Institutes of Health, Building 5, Bethesda, MD 20892-0520, USA.
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33
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A regular pattern of Ig super-motifs defines segmental flexibility as the elastic mechanism of the titin chain. Proc Natl Acad Sci U S A 2008; 105:1186-91. [PMID: 18212128 DOI: 10.1073/pnas.0707163105] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Myofibril elasticity, critical to muscle function, is dictated by the intrasarcomeric filament titin, which acts as a molecular spring. To date, the molecular events underlying the mechanics of the folded titin chain remain largely unknown. We have elucidated the crystal structure of the 6-Ig fragment I65-I70 from the elastic I-band fraction of titin and validated its conformation in solution using small angle x-ray scattering. The long-range properties of the chain have been visualized by electron microscopy on a 19-Ig fragment and modeled for the full skeletal tandem. Results show that conserved Ig-Ig transition motifs generate high-order in the structure of the filament, where conformationally stiff segments interspersed with pliant hinges form a regular pattern of dynamic super-motifs leading to segmental flexibility in the chain. Pliant hinges support molecular shape rearrangements that dominate chain behavior at moderate stretch, whereas stiffer segments predictably oppose high stretch forces upon full chain extension. There, librational entropy can be expected to act as an energy barrier to prevent Ig unfolding while, instead, triggering the unraveling of flanking springs formed by proline, glutamate, valine, and lysine (PEVK) sequences. We propose a mechanistic model based on freely jointed rigid segments that rationalizes the response to stretch of titin Ig-tandems according to molecular features.
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34
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Koch MHJ, Bras W. Synchrotron radiation studies of non-crystalline systems. ACTA ACUST UNITED AC 2008. [DOI: 10.1039/b703892p] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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35
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Lee EH, Hsin J, Mayans O, Schulten K. Secondary and tertiary structure elasticity of titin Z1Z2 and a titin chain model. Biophys J 2007; 93:1719-35. [PMID: 17496052 PMCID: PMC1948054 DOI: 10.1529/biophysj.107.105528] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2007] [Accepted: 04/10/2007] [Indexed: 11/18/2022] Open
Abstract
The giant protein titin, which is responsible for passive elasticity in muscle fibers, is built from approximately 300 regular immunoglobulin-like (Ig) domains and FN-III repeats. While the soft elasticity derived from its entropic regions, as well as the stiff mechanical resistance derived from the unfolding of the secondary structure elements of Ig- and FN-III domains have been studied extensively, less is known about the mechanical elasticity stemming from the orientation of neighboring domains relative to each other. Here we address the dynamics and energetics of interdomain arrangement of two adjacent Ig-domains of titin, Z1, and Z2, using molecular dynamics (MD) simulations. The simulations reveal conformational flexibility, due to the domain-domain geometry, that lends an intermediate force elasticity to titin. We employ adaptive biasing force MD simulations to calculate the energy required to bend the Z1Z2 tandem open to identify energetically feasible interdomain arrangements of the Z1 and Z2 domains. The finding is cast into a stochastic model for Z1Z2 interdomain elasticity that is generalized to a multiple domain chain replicating many Z1Z2-like units and representing a long titin segment. The elastic properties of this chain suggest that titin derives so-called tertiary structure elasticity from bending and twisting of its domains. Finally, we employ steered molecular dynamics simulations to stretch individual Z1 and Z2 domains and characterize the so-called secondary structure elasticity of the two domains. Our study suggests that titin's overall elastic response at weak force stems from a soft entropic spring behavior (not described here), from tertiary structure elasticity with an elastic spring constant of approximately 0.001-1 pN/A and, at strong forces, from secondary structure elasticity.
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Affiliation(s)
- Eric H Lee
- Center for Biophysics and Computational Biology and Beckman Institute, College of Medicine, Department of Physics and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL, USA
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36
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Müller S, Lange S, Gautel M, Wilmanns M. Rigid Conformation of an Immunoglobulin Domain Tandem Repeat in the A-band of the Elastic Muscle Protein Titin. J Mol Biol 2007; 371:469-80. [PMID: 17574571 DOI: 10.1016/j.jmb.2007.05.055] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2007] [Revised: 05/12/2007] [Accepted: 05/18/2007] [Indexed: 11/24/2022]
Abstract
Most of the structure of the giant muscle protein titin is formed by small modular domains. Many of them are predicted to be arranged in repeats with short linkers that may be key determinants of the peculiar elastic properties of titin. Here, we present the molecular structure of a tandem arrangement of two immunoglobulin-like domains, A168 and A169, located within the A-band segment of titin. The two domains are connected by a 17 residue long beta-strand and form a common interface. Based on these data, we establish general principles to estimate the amount of conformational flexibility of tandem domain motifs in titin. An unusual bulge within the second domain, A169, is directly involved into binding to a sarcomeric ligand, MURF-1, thus suggesting a dual role of this tandem for both the mechanical properties of titin and for sarcomeric signaling.
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Affiliation(s)
- Simone Müller
- EMBL Hamburg Outstation, c/o DESY, Notkestrasse 85, D-22603 Hamburg, Germany
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37
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Abstract
Single-molecule force experiments in vitro enable the characterization of the mechanical response of biological matter at the nanometer scale. However, they do not reveal the molecular mechanisms underlying mechanical function. These can only be readily studied through molecular dynamics simulations of atomic structural models: "in silico" (by computer analysis) single-molecule experiments. Steered molecular dynamics simulations, in which external forces are used to explore the response and function of macromolecules, have become a powerful tool complementing and guiding in vitro single-molecule experiments. The insights provided by in silico experiments are illustrated here through a review of recent research in three areas of protein mechanics: elasticity of the muscle protein titin and the extracellular matrix protein fibronectin; linker-mediated elasticity of the cytoskeleton protein spectrin; and elasticity of ankyrin repeats, a protein module found ubiquitously in cells but with an as-yet unclear function.
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Affiliation(s)
- Marcos Sotomayor
- Department of Physics, University of Illinois at Urbana-Champaign, and Beckman Institute for Advanced Science and Technology, 405 North Mathews Avenue, Urbana, IL 61801, USA
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38
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Mrosek M, Labeit D, Witt S, Heerklotz H, von Castelmur E, Labeit S, Mayans O. Molecular determinants for the recruitment of the ubiquitin-ligase MuRF-1 onto M-line titin. FASEB J 2007; 21:1383-92. [PMID: 17215480 DOI: 10.1096/fj.06-7644com] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Titin forms an intrasarcomeric filament system in vertebrate striated muscle, which has elastic and signaling properties and is thereby central to mechanotransduction. Near its C-terminus and directly preceding a kinase domain, titin contains a conserved pattern of Ig and FnIII modules (Ig(A168)-Ig(A169)-FnIII(A170), hereby A168-A170) that recruits the E3 ubiquitin-ligase MuRF-1 to the filament. This interaction is thought to regulate myofibril turnover and the trophic state of muscle. We have elucidated the crystal structure of A168-A170, characterized MuRF-1 variants by circular dichroism (CD) and SEC-MALS, and studied the interaction of both components by isothermal calorimetry, SPOTS blots, and pull-down assays. This has led to the identification of the molecular determinants of the binding. A168-A170 shows an extended, rigid architecture, which is characterized by a shallow surface groove that spans its full length and a distinct loop protrusion in its middle point. In MuRF-1, a C-terminal helical domain is sufficient to bind A168-A170 with high affinity. This helical region predictably docks into the surface groove of A168-A170. Furthermore, pull-down assays demonstrate that the loop protrusion in A168-A170 is a key mediator of MuRF-1 recognition. Our findings indicate that this region of titin could serve as a target to attempt therapeutic inhibition of MuRF-1-mediated muscle turnover, where binding of small molecules to its distinctive structural features could block MuRF-1 access.
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Affiliation(s)
- Michael Mrosek
- Division of Structural Biology, Biozentrum, University of Basel, Klingelbergstr. 70, CH-4056 Basel, Switzerland
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