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McCourt JL, Rhett KK, Jaeger MA, Belanto JJ, Talsness DM, Ervasti JM. In vitro stability of therapeutically relevant, internally truncated dystrophins. Skelet Muscle 2015; 5:13. [PMID: 25954502 PMCID: PMC4424174 DOI: 10.1186/s13395-015-0040-z] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2015] [Accepted: 04/14/2015] [Indexed: 12/21/2022] Open
Abstract
Background The X-linked recessive disease Duchenne muscular dystrophy (DMD) is caused by mutations in the gene encoding the protein dystrophin. Despite its large size, dystrophin is a highly stable protein, demonstrating cooperative unfolding during thermal denaturation as monitored by circular dichroism spectroscopy. In contrast, internal sequence deletions have been associated with a loss of the cooperative unfolding and cause in vitro protein aggregation. Several emerging therapy options for DMD utilize internally deleted micro-dystrophins and multi-exon-skipped dystrophins that produce partially functional proteins, but the stability of such internally truncated proteins has not been investigated. Methods In this study, we analyzed the in vitro stability of human dystrophin constructs skipped around exon 45 or exon 51, several dystrophin gene therapy constructs, as well as human full-length and micro-utrophin. Constructs were expressed in insect cells using the baculovirus system, purified by affinity chromatography, and analyzed by high-speed sedimentation, circular dichroism spectroscopy, and differential scanning fluorimetry. Results Our results reveal that not all gene therapy constructs display stabilities consistent with full-length human dystrophin. However, all dystrophins skipped in-frame around exon 45 or exon 51 show stability profiles congruent with intact human dystrophin. Similar to previous studies of mouse proteins, full-length human utrophin also displays stability similar to human dystrophin and does not appear to be affected by a large internal deletion. Conclusions Our results suggest that the in vitro stability of human dystrophin is less sensitive to smaller deletions at natural exon boundaries than larger, more complex deletions present in some gene therapy constructs.
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Affiliation(s)
- Jackie L McCourt
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota - Twin Cities, Minneapolis, MN 55455 USA
| | - Katrina K Rhett
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota - Twin Cities, Minneapolis, MN 55455 USA
| | - Michele A Jaeger
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota - Twin Cities, Minneapolis, MN 55455 USA
| | - Joseph J Belanto
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota - Twin Cities, Minneapolis, MN 55455 USA
| | - Dana M Talsness
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota - Twin Cities, Minneapolis, MN 55455 USA
| | - James M Ervasti
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota - Twin Cities, Minneapolis, MN 55455 USA
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2
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Exon edited dystrophin rods in the hinge 3 region. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2012; 1824:1080-9. [DOI: 10.1016/j.bbapap.2012.06.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2011] [Revised: 06/19/2012] [Accepted: 06/20/2012] [Indexed: 01/12/2023]
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3
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Muthu M, Richardson KA, Sutherland-Smith AJ. The crystal structures of dystrophin and utrophin spectrin repeats: implications for domain boundaries. PLoS One 2012; 7:e40066. [PMID: 22911693 PMCID: PMC3401230 DOI: 10.1371/journal.pone.0040066] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2012] [Accepted: 05/31/2012] [Indexed: 11/18/2022] Open
Abstract
Dystrophin and utrophin link the F-actin cytoskeleton to the cell membrane via an associated glycoprotein complex. This functionality results from their domain organization having an N-terminal actin-binding domain followed by multiple spectrin-repeat domains and then C-terminal protein-binding motifs. Therapeutic strategies to replace defective dystrophin with utrophin in patients with Duchenne muscular dystrophy require full-characterization of both these proteins to assess their degree of structural and functional equivalence. Here the high resolution structures of the first spectrin repeats (N-terminal repeat 1) from both dystrophin and utrophin have been determined by x-ray crystallography. The repeat structures both display a three-helix bundle fold very similar to one another and to homologous domains from spectrin, α-actinin and plectin. The utrophin and dystrophin repeat structures reveal the relationship between the structural domain and the canonical spectrin repeat domain sequence motif, showing the compact structural domain of spectrin repeat one to be extended at the C-terminus relative to its previously defined sequence repeat. These structures explain previous in vitro biochemical studies in which extending dystrophin spectrin repeat domain length leads to increased protein stability. Furthermore we show that the first dystrophin and utrophin spectrin repeats have no affinity for F-actin in the absence of other domains.
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Affiliation(s)
- Muralidharan Muthu
- Institute of Molecular BioSciences, Massey University, Palmerston North, New Zealand
| | - Kylie A. Richardson
- Institute of Molecular BioSciences, Massey University, Palmerston North, New Zealand
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4
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A new twist to coiled coil. FEBS Lett 2012; 586:2717-22. [DOI: 10.1016/j.febslet.2012.05.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2012] [Revised: 05/02/2012] [Accepted: 05/03/2012] [Indexed: 01/21/2023]
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5
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Adkin CF, Meloni PL, Fletcher S, Adams AM, Muntoni F, Wong B, Wilton SD. Multiple exon skipping strategies to by-pass dystrophin mutations. Neuromuscul Disord 2011; 22:297-305. [PMID: 22182525 PMCID: PMC3488593 DOI: 10.1016/j.nmd.2011.10.007] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2011] [Revised: 10/10/2011] [Accepted: 10/11/2011] [Indexed: 11/24/2022]
Abstract
Manipulation of dystrophin pre-mRNA processing offers the potential to overcome mutations in the dystrophin gene that would otherwise lead to Duchenne muscular dystrophy. Dystrophin mutations will require the removal of one or more exons to restore the reading frame and in some cases, multiple exon skipping strategies exist to restore dystrophin expression. However, for some small intra-exonic mutations, a third strategy, not applicable to whole exon deletions, may be possible. The removal of only one frame-shifting exon flanking the mutation-carrying exon may restore the reading frame and allow synthesis of a functional dystrophin isoform, providing that no premature termination codons are encountered. For these mutations, the removal of only one exon offers a simpler, cheaper and more feasible alternative approach to the dual exon skipping that would otherwise be considered. We present strategies to by-pass intra-exonic dystrophin mutations that clearly demonstrate the importance of tailoring exon skipping strategies to specific patient mutations.
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Affiliation(s)
- Carl F Adkin
- Centre for Neuromuscular and Neurological Disorders, University of Western Australia, Perth, WA 6009, Australia
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6
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Legrand B, Giudice E, Nicolas A, Delalande O, Le Rumeur E. Computational study of the human dystrophin repeats: interaction properties and molecular dynamics. PLoS One 2011; 6:e23819. [PMID: 21901138 PMCID: PMC3162007 DOI: 10.1371/journal.pone.0023819] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2011] [Accepted: 07/26/2011] [Indexed: 01/16/2023] Open
Abstract
Dystrophin is a large protein involved in the rare genetic disease Duchenne muscular dystrophy (DMD). It functions as a mechanical linker between the cytoskeleton and the sarcolemma, and is able to resist shear stresses during muscle activity. In all, 75% of the dystrophin molecule consists of a large central rod domain made up of 24 repeat units that share high structural homology with spectrin-like repeats. However, in the absence of any high-resolution structure of these repeats, the molecular basis of dystrophin central domain's functions has not yet been deciphered. In this context, we have performed a computational study of the whole dystrophin central rod domain based on the rational homology modeling of successive and overlapping tandem repeats and the analysis of their surface properties. Each tandem repeat has very specific surface properties that make it unique. However, the repeats share enough electrostatic-surface similarities to be grouped into four separate clusters. Molecular dynamics simulations of four representative tandem repeats reveal specific flexibility or bending properties depending on the repeat sequence. We thus suggest that the dystrophin central rod domain is constituted of seven biologically relevant sub-domains. Our results provide evidence for the role of the dystrophin central rod domain as a scaffold platform with a wide range of surface features and biophysical properties allowing it to interact with its various known partners such as proteins and membrane lipids. This new integrative view is strongly supported by the previous experimental works that investigated the isolated domains and the observed heterogeneity of the severity of dystrophin related pathologies, especially Becker muscular dystrophy.
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Affiliation(s)
- Baptiste Legrand
- Université de Rennes 1, Rennes, France
- Equipe RMN-ILP, Faculté de médecine, UMR CNRS 6026, Rennes, France
- Université Européenne de Bretagne, Rennes, France
| | - Emmanuel Giudice
- Université de Rennes 1, Rennes, France
- Equipe SDM, UMR CNRS 6026, Rennes, France
- Université Européenne de Bretagne, Rennes, France
| | - Aurélie Nicolas
- Université de Rennes 1, Rennes, France
- Equipe RMN-ILP, Faculté de médecine, UMR CNRS 6026, Rennes, France
- Université Européenne de Bretagne, Rennes, France
| | - Olivier Delalande
- Université de Rennes 1, Rennes, France
- Equipe RMN-ILP, Faculté de médecine, UMR CNRS 6026, Rennes, France
- Université Européenne de Bretagne, Rennes, France
| | - Elisabeth Le Rumeur
- Université de Rennes 1, Rennes, France
- Equipe RMN-ILP, Faculté de médecine, UMR CNRS 6026, Rennes, France
- Université Européenne de Bretagne, Rennes, France
- * E-mail:
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Mirza A, Sagathevan M, Sahni N, Choi L, Menhart N. A biophysical map of the dystrophin rod. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2010; 1804:1796-809. [DOI: 10.1016/j.bbapap.2010.03.009] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2010] [Revised: 03/16/2010] [Accepted: 03/24/2010] [Indexed: 11/26/2022]
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8
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Dystrophin: more than just the sum of its parts. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2010; 1804:1713-22. [PMID: 20472103 DOI: 10.1016/j.bbapap.2010.05.001] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2010] [Revised: 04/30/2010] [Accepted: 05/03/2010] [Indexed: 01/05/2023]
Abstract
Dystrophin is one of a number of large cytoskeleton associated proteins that connect between various cytoskeletal elements and often are tethered to the membrane through other transmembrane protein complexes. These cytolinker proteins often provide structure and support to the cells where they are expressed, and mutations in genes encoding these proteins frequently gives rise to disease. Dystrophin is no exception in any of these respects, providing connections between a transmembrane complex known as the dystrophin-glycoprotein complex and the underlying cytoskeleton. The most established connection and possibly the most important is that to F-actin, but more recently evidence has been forthcoming of connections to membrane phospholipids, intermediate filaments and microtubules. Moreover it is becoming increasingly clear that the multiple spectrin-like repeats in the centre of the molecule, that had hitherto been thought to be largely redundant, harbour binding activities that have a significant impact on dystrophin functionality. This functionality is particularly apparent when assessed by the ability to rescue the dystrophic phenotype in mdx mice. This review will focus on the relatively neglected but functionally vital coiled-coil region of dystrophin, highlighting the structural relationships and interactions of the coiled-coil region and providing new insights into the functional role of this region.
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Banks GB, Judge LM, Allen JM, Chamberlain JS. The polyproline site in hinge 2 influences the functional capacity of truncated dystrophins. PLoS Genet 2010; 6:e1000958. [PMID: 20502633 PMCID: PMC2873924 DOI: 10.1371/journal.pgen.1000958] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2009] [Accepted: 04/20/2010] [Indexed: 01/01/2023] Open
Abstract
Mutations in dystrophin can lead to Duchenne muscular dystrophy or the more mild form of the disease, Becker muscular dystrophy. The hinge 3 region in the rod domain of dystrophin is particularly prone to deletion mutations. In-frame deletions of hinge 3 are predicted to lead to BMD, however the severity of disease can vary considerably. Here we performed extensive structure-function analyses of truncated dystrophins with modified hinges and spectrin-like repeats in mdx mice. We found that the polyproline site in hinge 2 profoundly influences the functional capacity of a microdystrophin(DeltaR4-R23/DeltaCT) with a large deletion in the hinge 3 region. Inclusion of polyproline in microdystrophin(DeltaR4-R23/DeltaCT) led to small myofibers (12% smaller than wild-type), Achilles myotendinous disruption, ringed fibers, and aberrant neuromuscular junctions in the mdx gastrocnemius muscles. Replacing hinge 2 of microdystrophin(DeltaR4-R23/DeltaCT) with hinge 3 significantly improved the functional capacity to prevent muscle degeneration, increase muscle fiber area, and maintain the junctions. We conclude that the rigid alpha-helical structure of the polyproline site significantly impairs the functional capacity of truncated dystrophins to maintain appropriate connections between the cytoskeleton and extracellular matrix.
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Affiliation(s)
- Glen B. Banks
- Department of Neurology, Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center, University of Washington, Seattle, Washington, United States of America
| | - Luke M. Judge
- Department of Neurology, Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center, University of Washington, Seattle, Washington, United States of America
| | - James M. Allen
- Department of Neurology, Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center, University of Washington, Seattle, Washington, United States of America
- Department of Medicine, University of Washington, Seattle, Washington, United States of America
| | - Jeffrey S. Chamberlain
- Department of Neurology, Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center, University of Washington, Seattle, Washington, United States of America
- Department of Medicine, University of Washington, Seattle, Washington, United States of America
- Department of Biochemistry, University of Washington, Seattle, Washington, United States of America
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10
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Disease-causing missense mutations in actin binding domain 1 of dystrophin induce thermodynamic instability and protein aggregation. Proc Natl Acad Sci U S A 2010; 107:9632-7. [PMID: 20457930 DOI: 10.1073/pnas.1001517107] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mutations in the dystrophin gene cause Duchenne muscular dystrophy (DMD) most commonly through loss of protein expression. In a small subpopulation of patients, missense mutations can cause DMD, Becker muscular dystrophy, or X-linked cardiomyopathy. Nearly one-half of disease-causing missense mutations are located in actin-binding domain 1 (ABD1) of dystrophin. To test the hypothesis that ABD1 missense mutations cause disease by impairing actin-binding activity, we engineered the K18N, L54R, D165V, A168D, L172H, and Y231N mutations into the full-length dystrophin cDNA and characterized the biochemical properties of each mutant protein. The K18N and L54R mutations are associated with the most severe diseases in humans and each caused a small but significant 4-fold decrease in actin-binding affinity, while the affinities of the other four mutant proteins were not significantly different from WT dystrophin. More interestingly, WT dystrophin was observed to unfold in a single-step, highly cooperative manner. In contrast, all six mutant proteins were significantly more prone to thermal denaturation and aggregation. Our results suggest that missense mutations in ABD1 may all cause loss of dystrophin function via protein instability and aggregation rather than through loss of ligand binding function. However, more severe disease progressions may be due to the combinatorial effects of some mutations on both protein aggregation and impaired actin-binding activity.
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11
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Legardinier S, Raguénès-Nicol C, Tascon C, Rocher C, Hardy S, Hubert JF, Le Rumeur E. Mapping of the lipid-binding and stability properties of the central rod domain of human dystrophin. J Mol Biol 2009; 389:546-58. [PMID: 19379759 DOI: 10.1016/j.jmb.2009.04.025] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2009] [Revised: 03/31/2009] [Accepted: 04/11/2009] [Indexed: 11/28/2022]
Abstract
Dystrophin is a cytoskeletal protein that confers resistance to the sarcolemma against the stress of contraction-relaxation cycles by interacting with cytoskeletal and membrane partners. Apart from several proteins, membrane phospholipids are a partner of the central rod domain made up of 24 spectrin-like repeats, separated into sub-domains by four hinges. We previously showed that repeats 1 to 3 bind to membrane anionic phospholipids, while repeats 20 to 24 are not able to do so. We focus here on the phospholipid-binding properties of the major part of the central rod domain, namely, the sub-domain delineated by hinges 2 and 3 comprising 16 repeats ranging from repeat 4 to 19 (R4-19). We designed and produced multirepeat proteins comprising three to five repeats and report their lipid-binding properties as well as their thermal stabilities. When these proteins are mixed with liposomes including the anionic lipid phosphatidylserine, they form stable protein-vesicle complexes as determined by gel-filtration chromatography. The absence of an anionic lipid precludes the formation of such complexes. Spectroscopic analyses by circular dichroism and tryptophan fluorescence show that, while the alpha-helical secondary structures are not modified by the binding, protein trans conformation leads to the movement of tryptophan residues into more hydrophobic environments. In addition, the decrease in the molar ellipticity ratio at 222/208 nm as observed by circular dichroism indicates that lipid binding reduces the inter-helical interactions of multirepeat proteins, thus suggesting partly "opened" coiled-coil structures. Combining these results with data from our previous studies, we propose a new model of the dystrophin molecule lying along the membrane bilayer, in which the two sub-domains R1-3 and R4-19 interact with lipids and F-actin, while the distal sub-domain R20-24 does not exhibit any interaction. These lipid-binding domains should thus maintain a structural link between cytoskeletal actin and sarcolemma via the membrane phospholipids.
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Affiliation(s)
- Sébastien Legardinier
- Université de Rennes 1, UMR CNRS 6026, Interactions cellulaires et moléculaires, IFR 140, Faculté de Médecine, CS 34317, 35043 Rennes Cedex, France
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12
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Ruszczak C, Mirza A, Menhart N. Differential stabilities of alternative exon-skipped rod motifs of dystrophin. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2009; 1794:921-8. [PMID: 19286484 DOI: 10.1016/j.bbapap.2009.02.016] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2008] [Revised: 02/16/2009] [Accepted: 02/27/2009] [Indexed: 11/26/2022]
Abstract
Exon skipping repair is a strategy being investigated in early stage clinical trials to treat Duchenne muscular dystrophy. This is most applicable to the majority of cases which arise when genetic defects cause frame shift mutations, and induced exon skipping of out-of-phase exons restores the reading frame. However, the consequences to the edited protein so produced have not been considered. In many cases alternative routes to restoring the reading frame are possible, and we show in a test case involving exon 44 that the resulting differently edited proteins greatly vary in stability, with one of them very similar to normal unskipped dystrophin, and the other much less stable as assessed by the thermodynamics of folding as well as resistance to proteolysis. This has implications for the design of optimal therapeutic exon skipping strategies, which presumably wish to result repairs with as much fidelity to normal dystrophin as possible.
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Affiliation(s)
- Chris Ruszczak
- Division of Biology, Illinois Institute of Technology, Chicago IL 60616, USA
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The value of mammalian models for duchenne muscular dystrophy in developing therapeutic strategies. Curr Top Dev Biol 2009; 84:431-53. [PMID: 19186250 DOI: 10.1016/s0070-2153(08)00609-1] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Duchenne muscular dystrophy (DMD) is the most common form of muscular dystrophy. There is no effective treatment and patients typically die in approximately the third decade. DMD is an X-linked recessive disease caused by mutations in the dystrophin gene. There are three mammalian models of DMD that have been used to understand better the pathogenesis of disease and develop therapeutic strategies. The mdx mouse is the most widely used model of DMD that displays some features of muscle degeneration, but the pathogenesis of disease is comparatively mild. The severity of disease in mice lacking both dystrophin and utrophin is similar to DMD, but one has to account for the discrete functions of utrophin. Canine X-linked muscular dystrophy (cxmd) is the best representation of DMD, but the phenotype of the most widely used golden retriever (GRMD) model is variable, making functional endpoints difficult to ascertain. Although each mammalian model has its limitations, together they have been essential for the development of several treatment strategies for DMD that target dystrophin replacement, disease progression, and muscle regeneration.
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Legardinier S, Legrand B, Raguénès-Nicol C, Bondon A, Hardy S, Tascon C, Le Rumeur E, Hubert JF. A Two-amino Acid Mutation Encountered in Duchenne Muscular Dystrophy Decreases Stability of the Rod Domain 23 (R23) Spectrin-like Repeat of Dystrophin. J Biol Chem 2009; 284:8822-32. [PMID: 19158079 DOI: 10.1074/jbc.m805846200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Lack of functional dystrophin causes severe Duchenne muscular dystrophy. The subsarcolemmal location of dystrophin, as well as its association with both cytoskeleton and membrane, suggests a role in the mechanical regulation of muscular membrane stress. In particular, phenotype rescue in a Duchenne muscular dystrophy mice model has shown that some parts of the central rod domain of dystrophin, constituted by 24 spectrin-like repeats, are essential. In this study, we made use of rare missense pathogenic mutations in the dystrophin gene and analyzed the biochemical properties of the isolated repeat 23 bearing single or double mutations E2910V and N2912D found in muscle dystrophy with severity grading. No dramatic effect on secondary and tertiary structure of the repeat was found in mutants compared with wild type as revealed by circular dichroism and NMR. Thermal and chemical unfolding data from circular dichroism and tryptophan fluorescence show significant decrease of stability for the mutants, and stopped-flow spectroscopy shows decreased refolding rates. The most deleterious single mutation is the N2912D replacement, although we observe additive effects of the two mutations on repeat stability. Based on three-dimensional structures built by homology molecular modeling, we discuss the modifications of the mutation-induced repeat stability. We conclude that the main forces involved in repeat stability are electrostatic inter-helix interactions that are disrupted following mutations. This study represents the first analysis at the protein level of the consequences of missense mutations in the human dystrophin rod domain. Our results suggest that it may participate in mechanical weakening of dystrophin-deficient muscle.
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Affiliation(s)
- Sébastien Legardinier
- UMR CNRS 6026 Interactions Cellulaires et Moléculaires,Equipe RMN et Interactions Lipides-Protéines and UMR CNRS 6061 Génétique et Développement, Université de Rennes 1, IFR 140, FacultédeMédecine, CS 34317, 35043 Rennes Cedex, France
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15
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Mirza A, Menhart N. Stability of dystrophin STR fragments in relation to junction helicity. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2008; 1784:1301-9. [PMID: 18589007 DOI: 10.1016/j.bbapap.2008.05.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2008] [Revised: 04/22/2008] [Accepted: 05/19/2008] [Indexed: 11/16/2022]
Abstract
Dystrophin is a rod shaped protein consisting of amino- and carboxy-terminal binding domains linked by a large central rod composed of 24 homologous copies of the STR motif and 4 non-homologous regions termed hinges. These hinges are proposed to confer local flexibility; conversely, the tacit implication is that the STR regions away from the hinges are comparatively rigid. This, and the repeating nature of this rod, has contributed to the view that the STR region of the rod is uniform and monolithic. However, we have produced various 2 STR fragments, chosen to have high and low alpha-helix content at their junctions with each other, and show that they exhibit markedly different stabilities. In contrast to a related protein, spectrin, these differences are not correlated with the calculated helicity, but appear to be an intrinsic property of the motifs themselves. A full understanding of how these properties vary along the length of the rod has implications for the engineering of these rods regions in exon skipping and minidystrophin therapies.
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Affiliation(s)
- Ahmed Mirza
- Department of Biological, Chemical and Physical Sciences, Illinois Institute of Technology, 3101 South Dearborn, Chicago, IL 60616, USA
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16
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Legardinier S, Hubert JF, Bihan OL, Tascon C, Rocher C, Raguénès-Nicol C, Bondon A, Hardy S, Rumeur EL. Sub-domains of the dystrophin rod domain display contrasting lipid-binding and stability properties. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2008; 1784:672-82. [DOI: 10.1016/j.bbapap.2007.12.014] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2007] [Revised: 12/12/2007] [Accepted: 12/24/2007] [Indexed: 10/22/2022]
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17
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Suchyna TM, Sachs F. Mechanosensitive channel properties and membrane mechanics in mouse dystrophic myotubes. J Physiol 2007; 581:369-87. [PMID: 17255168 PMCID: PMC2075208 DOI: 10.1113/jphysiol.2006.125021] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Muscular dystrophy is associated with increased activity of mechanosensitive channels (MSCs) and increased cell calcium levels. MSCs in patches from mdx mouse myotubes have higher levels of resting activity, compared to patches from wild-type mice, and a pronounced latency of activation and deactivation. Measurements of patch capacitance and geometry reveal that the differences are linked to cortical membrane mechanics rather than to differences in channel gating. We found unexpectedly that patches from mdx mice are strongly curved towards the pipette tip by actin pulling normal to the membrane. This force produces a substantial tension (approximately 5 mN m(-1)) that can activate MSCs in the absence of overt stimulation. The inward curvature of patches from mdx mice is eliminated by actin inhibitors. Applying moderate suction to the pipette flattens the membrane, reducing tension, and making the response appear to be stretch inactivated. The pronounced latency to activation in patches from mdx mice is caused by the mechanical relaxation time required to reorganize the cortex from inward to outward curvature. The increased latency is equivalent to a three-fold increase in cortical viscosity. Disruption of the cytoskeleton by chemical or mechanical means eliminates the differences in kinetics and curvature between patches from wild-type and mdx mice. The stretch-induced increase in specific capacitance of the patch, approximately 80 fF microm(-2), far exceeds the specific capacitance of bilayers, suggesting the presence of stress-sensitive access to large pools of membrane, possibly caveoli, T-tubules or portions of the gigaseal. In mdx mouse cells the intrinsic gating property of fast voltage-sensitive inactivation is lost. It is robust in wild-type mouse cells (observed in 50% of outside-out patches), but never observed in mdx cells. This link between dystrophin and inactivation may lead to increased background cation currents and Ca2+ influx. Spontaneous Ca2+ transients in mdx mouse cells are sensitive to depolarization and are inhibited by the specific MSC inhibitor GsMTx4, in both the D and L forms.
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Affiliation(s)
- Thomas M Suchyna
- Department of Physiology and Biophysics, Center for Single Molecule Biophysics, State University New York (SUNY) at Buffalo, Buffalo, NY 14214, USA.
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