1
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Roopnarine O, Thomas DD. Structural Dynamics of Protein Interactions Using Site-Directed Spin Labeling of Cysteines to Measure Distances and Rotational Dynamics with EPR Spectroscopy. APPLIED MAGNETIC RESONANCE 2024; 55:79-100. [PMID: 38371230 PMCID: PMC10868710 DOI: 10.1007/s00723-023-01623-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2023] [Revised: 09/19/2023] [Accepted: 09/22/2023] [Indexed: 02/20/2024]
Abstract
Here we review applications of site-directed spin labeling (SDSL) with engineered cysteines in proteins, to study the structural dynamics of muscle and non-muscle proteins, using and developing the electron paramagnetic resonance (EPR) spectroscopic techniques of dipolar EPR, double electron electron resonance (DEER), saturation transfer EPR (STEPR), and orientation measured by EPR. The SDSL technology pioneered by Wayne Hubbell and collaborators has greatly expanded the use of EPR, including the measurement of distances between spin labels covalently attached to proteins and peptides. The Thomas lab and collaborators have applied these techniques to elucidate dynamic interactions in the myosin-actin complex, myosin-binding protein C, calmodulin, ryanodine receptor, phospholamban, utrophin, dystrophin, β-III-spectrin, and Aurora kinase. The ability to design and engineer cysteines in proteins for site-directed covalent labeling has enabled the use of these powerful EPR techniques to measure distances, while showing that they are complementary with optical spectroscopy measurements.
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Affiliation(s)
- Osha Roopnarine
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
| | - David D. Thomas
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
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2
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Fischer NC, Friedman V, Martinez-Reyes MA, Hao H, Chowdhury TA, Starr DA, Quinn CC. The ANC-1 (Nesprin-1/2) organelle-anchoring protein functions through mitochondria to polarize axon growth in response to SLT-1. PLoS Genet 2022; 18:e1010521. [PMID: 36409768 PMCID: PMC9721489 DOI: 10.1371/journal.pgen.1010521] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Revised: 12/05/2022] [Accepted: 11/11/2022] [Indexed: 11/22/2022] Open
Abstract
A family of giant KASH proteins, including C. elegans ANC-1 and mammalian Nesprin-1 and -2, are involved in organelle anchoring and are associated with multiple neurodevelopmental disorders including autism, bipolar disorder, and schizophrenia. However, little is known about how these proteins function in neurons. Moreover, the role of organelle anchoring in axon development is poorly understood. Here, we report that ANC-1 functions with the SLT-1 extracellular guidance cue to polarize ALM axon growth. This role for ANC-1 is specific to its longer ANC-1A and ANC-1C isoforms, suggesting that it is mechanistically distinct from previously described roles for ANC-1. We find that ANC-1 is required for the localization of a cluster of mitochondria to the base of the proximal axon. Furthermore, genetic and pharmacological studies indicate that ANC-1 functions with mitochondria to promote polarization of ALM axon growth. These observations reveal a mechanism whereby ANC-1 functions through mitochondria to polarize axon growth in response to SLT-1.
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Affiliation(s)
- Nathan C. Fischer
- Department of Biological Sciences, University of Wisconsin-Milwaukee; Milwaukee, Wisconsin, United States of America
| | - Vladislav Friedman
- Department of Biological Sciences, University of Wisconsin-Milwaukee; Milwaukee, Wisconsin, United States of America
| | - Miguel A. Martinez-Reyes
- Department of Biological Sciences, University of Wisconsin-Milwaukee; Milwaukee, Wisconsin, United States of America
| | - Hongyan Hao
- Department of Molecular and Cellular Biology, University of California, Davis, California, United States of America
| | - Tamjid A. Chowdhury
- Department of Biological Sciences, University of Wisconsin-Milwaukee; Milwaukee, Wisconsin, United States of America
| | - Daniel A. Starr
- Department of Molecular and Cellular Biology, University of California, Davis, California, United States of America
| | - Christopher C. Quinn
- Department of Biological Sciences, University of Wisconsin-Milwaukee; Milwaukee, Wisconsin, United States of America
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3
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Morita R, Nakano K, Shigeta Y, Harada R. Molecular Mechanism for the Actin-Binding Domain of α-Actinin Ain1 Elucidated by Molecular Dynamics Simulations and Mutagenesis Experiments. J Phys Chem B 2020; 124:8495-8503. [DOI: 10.1021/acs.jpcb.0c04623] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Rikuri Morita
- Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8572, Japan
- Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
| | - Kentaro Nakano
- Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8572, Japan
| | - Yasuteru Shigeta
- Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
| | - Ryuhei Harada
- Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8577, Japan
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4
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Structural basis for high-affinity actin binding revealed by a β-III-spectrin SCA5 missense mutation. Nat Commun 2017; 8:1350. [PMID: 29116080 PMCID: PMC5676748 DOI: 10.1038/s41467-017-01367-w] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2017] [Accepted: 09/08/2017] [Indexed: 12/24/2022] Open
Abstract
Spinocerebellar ataxia type 5 (SCA5) is a neurodegenerative disease caused by mutations in the cytoskeletal protein β-III-spectrin. Previously, a SCA5 mutation resulting in a leucine-to-proline substitution (L253P) in the actin-binding domain (ABD) was shown to cause a 1000-fold increase in actin-binding affinity. However, the structural basis for this increase is unknown. Here, we report a 6.9 Å cryo-EM structure of F-actin complexed with the L253P ABD. This structure, along with co-sedimentation and pulsed-EPR measurements, demonstrates that high-affinity binding caused by the CH2-localized mutation is due to opening of the two CH domains. This enables CH1 to bind actin aided by an unstructured N-terminal region that becomes α-helical upon binding. This helix is required for association with actin as truncation eliminates binding. Collectively, these results shed light on the mechanism by which β-III-spectrin, and likely similar actin-binding proteins, interact with actin, and how this mechanism can be perturbed to cause disease.
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5
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Kyrychenko V, Kyrychenko S, Tiburcy M, Shelton JM, Long C, Schneider JW, Zimmermann WH, Bassel-Duby R, Olson EN. Functional correction of dystrophin actin binding domain mutations by genome editing. JCI Insight 2017; 2:95918. [PMID: 28931764 DOI: 10.1172/jci.insight.95918] [Citation(s) in RCA: 70] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Accepted: 08/15/2017] [Indexed: 12/26/2022] Open
Abstract
Dystrophin maintains the integrity of striated muscles by linking the actin cytoskeleton with the cell membrane. Duchenne muscular dystrophy (DMD) is caused by mutations in the dystrophin gene (DMD) that result in progressive, debilitating muscle weakness, cardiomyopathy, and a shortened lifespan. Mutations of dystrophin that disrupt the amino-terminal actin-binding domain 1 (ABD-1), encoded by exons 2-8, represent the second-most common cause of DMD. In the present study, we compared three different strategies for CRISPR/Cas9 genome editing to correct mutations in the ABD-1 region of the DMD gene by deleting exons 3-9, 6-9, or 7-11 in human induced pluripotent stem cells (iPSCs) and by assessing the function of iPSC-derived cardiomyocytes. All three exon deletion strategies enabled the expression of truncated dystrophin protein and restoration of cardiomyocyte contractility and calcium transients to varying degrees. We show that deletion of exons 3-9 by genomic editing provides an especially effective means of correcting disease-causing ABD-1 mutations. These findings represent an important step toward eventual correction of common DMD mutations and provide a means of rapidly assessing the expression and function of internally truncated forms of dystrophin-lacking portions of ABD-1.
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Affiliation(s)
- Viktoriia Kyrychenko
- Department of Molecular Biology.,Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center, and.,Hamon Center for Regenerative Science and Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Sergii Kyrychenko
- Department of Molecular Biology.,Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center, and.,Hamon Center for Regenerative Science and Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Malte Tiburcy
- Institute of Pharmacology and Toxicology, University Medical Center Göttingen, Göttingen, Germany.,DZHK (German Center for Cardiovascular Research), Partner Site Göttingen, Göttingen, Germany
| | - John M Shelton
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Chengzu Long
- Department of Molecular Biology.,Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center, and.,Hamon Center for Regenerative Science and Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Jay W Schneider
- Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center, and.,Hamon Center for Regenerative Science and Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA.,Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Wolfram-Hubertus Zimmermann
- Institute of Pharmacology and Toxicology, University Medical Center Göttingen, Göttingen, Germany.,DZHK (German Center for Cardiovascular Research), Partner Site Göttingen, Göttingen, Germany
| | - Rhonda Bassel-Duby
- Department of Molecular Biology.,Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center, and.,Hamon Center for Regenerative Science and Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Eric N Olson
- Department of Molecular Biology.,Senator Paul D. Wellstone Muscular Dystrophy Cooperative Research Center, and.,Hamon Center for Regenerative Science and Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA
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6
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Delalande O, Czogalla A, Hubert JF, Sikorski A, Le Rumeur E. Dystrophin and Spectrin, Two Highly Dissimilar Sisters of the Same Family. Subcell Biochem 2017; 82:373-403. [PMID: 28101868 DOI: 10.1007/978-3-319-49674-0_12] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Dystrophin and Spectrin are two proteins essential for the organization of the cytoskeleton and for the stabilization of membrane cells. The comparison of these two sister proteins, and with the dystrophin homologue utrophin, enables us to emphasise that, despite a similar topology with common subdomains and a common structural basis of a three-helix coiled-coil, they show a large range of dissimilarities in terms of genetics, cell expression and higher level structural organisation. Interactions with cellular partners, including proteins and membrane phospholipids, also show both strikingly similar and very different behaviours. The differences between dystrophin and spectrin are also illustrated by the large variety of pathological anomalies emerging from the dysfunction or the absence of these proteins, showing that they are keystones in their function of providing a scaffold that sustains cell structure.
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Affiliation(s)
- Olivier Delalande
- Institut de Génétique et Développement de Rennes, UMR CNRS 6290, Université de Rennes 1, Rennes, France.
| | - Aleksander Czogalla
- Biotechnology Faculty, Department of Cytobiochemistry, University of Wrocław, ul. joliot-Curie 14a, 50-383, Wroclaw, Poland
| | - Jean-François Hubert
- Institut de Génétique et Développement de Rennes, UMR CNRS 6290, Université de Rennes 1, Rennes, France
| | - Aleksander Sikorski
- Biotechnology Faculty, Department of Cytobiochemistry, University of Wrocław, ul. joliot-Curie 14a, 50-383, Wroclaw, Poland
| | - Elisabeth Le Rumeur
- Institut de Génétique et Développement de Rennes, UMR CNRS 6290, Université de Rennes 1, Rennes, France
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7
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Wang P, Liu H, Wang Y, Liu O, Zhang J, Gleason A, Yang Z, Wang H, Shi A, Grant BD. RAB-10 Promotes EHBP-1 Bridging of Filamentous Actin and Tubular Recycling Endosomes. PLoS Genet 2016; 12:e1006093. [PMID: 27272733 PMCID: PMC4894640 DOI: 10.1371/journal.pgen.1006093] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2015] [Accepted: 05/10/2016] [Indexed: 12/21/2022] Open
Abstract
EHBP-1 (Ehbp1) is a conserved regulator of endocytic recycling, acting as an effector of small GTPases including RAB-10 (Rab10). Here we present evidence that EHBP-1 associates with tubular endosomal phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2] enriched membranes through an N-terminal C2-like (NT-C2) domain, and define residues within the NT-C2 domain that mediate membrane interaction. Furthermore, our results indicate that the EHBP-1 central calponin homology (CH) domain binds to actin microfilaments in a reaction that is stimulated by RAB-10(GTP). Loss of any aspect of this RAB-10/EHBP-1 system in the C. elegans intestinal epithelium leads to retention of basolateral recycling cargo in endosomes that have lost their normal tubular endosomal network (TEN) organization. We propose a mechanism whereby RAB-10 promotes the ability of endosome-bound EHBP-1 to also bind to the actin cytoskeleton, thereby promoting endosomal tubulation. Endosomes are intracellular organelles that sort protein and lipid components integral to the membrane, as well as more loosely associated lumenal content, for delivery to distinct intracellular destinations. Endosomes associated with recycling cargo back to the plasma membrane are often tubular in morphology, and this morphology is thought to be essential for recycling function. Our previous work identified a particularly dramatic network of endosomal tubules involved in membrane protein recycling in the basolateral intestinal epithelial cells of C. elegans. Our subsequent genetic analysis of basolateral recycling in this system identified a number of key regulators of these endosomes, including the small GTPase RAB-10 and its effector EHBP-1. Our new work presented here shows that EHBP-1 promotes endosomal tubulation by linking the membrane lipid PI(4,5)P2 to the actin cytoskeleton, and that the linkage of EHBP-1 to actin is enhanced by the interaction of EHBP-1 with RAB-10. This work has broad implications for how endosomal tubulation occurs in all cells, and has specific implications for the role of EHBP-1 in related processes such as insulin-stimulated recycling of glucose transporters in human adipocytes, a process intimately linked to type II diabetes.
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Affiliation(s)
- Peixiang Wang
- Department of Medical Genetics, School of Basic Medicine and the Collaborative Innovation Center for Brain Science, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Hang Liu
- Department of Medical Genetics, School of Basic Medicine and the Collaborative Innovation Center for Brain Science, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Yu Wang
- Department of Medical Genetics, School of Basic Medicine and the Collaborative Innovation Center for Brain Science, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Ou Liu
- Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey, United States of America
| | - Jing Zhang
- Department of Medical Genetics, School of Basic Medicine and the Collaborative Innovation Center for Brain Science, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Adenrele Gleason
- Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey, United States of America
| | - Zhenrong Yang
- Department of Medical Genetics, School of Basic Medicine and the Collaborative Innovation Center for Brain Science, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Hui Wang
- Department of Medical Genetics, School of Basic Medicine and the Collaborative Innovation Center for Brain Science, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Anbing Shi
- Department of Medical Genetics, School of Basic Medicine and the Collaborative Innovation Center for Brain Science, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
- Institute for Brain Research, Huazhong University of Science and Technology, Wuhan, Hubei, China
- Key Laboratory of Neurological Disease of National Education Ministry, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
- * E-mail: (AS); (BDG)
| | - Barth D. Grant
- Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey, United States of America
- * E-mail: (AS); (BDG)
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8
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Mechanoaccumulative Elements of the Mammalian Actin Cytoskeleton. Curr Biol 2016; 26:1473-1479. [PMID: 27185555 DOI: 10.1016/j.cub.2016.04.007] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2015] [Revised: 02/16/2016] [Accepted: 04/01/2016] [Indexed: 11/20/2022]
Abstract
To change shape, divide, form junctions, and migrate, cells reorganize their cytoskeletons in response to changing mechanical environments [1-4]. Actin cytoskeletal elements, including myosin II motors and actin crosslinkers, structurally remodel and activate signaling pathways in response to imposed stresses [5-9]. Recent studies demonstrate the importance of force-dependent structural rearrangement of α-catenin in adherens junctions [10] and vinculin's molecular clutch mechanism in focal adhesions [11]. However, the complete landscape of cytoskeletal mechanoresponsive proteins and the mechanisms by which these elements sense and respond to force remain to be elucidated. To find mechanosensitive elements in mammalian cells, we examined protein relocalization in response to controlled external stresses applied to individual cells. Here, we show that non-muscle myosin II, α-actinin, and filamin accumulate to mechanically stressed regions in cells from diverse lineages. Using reaction-diffusion models for force-sensitive binding, we successfully predicted which mammalian α-actinin and filamin paralogs would be mechanoaccumulative. Furthermore, a "Goldilocks zone" must exist for each protein where the actin-binding affinity must be optimal for accumulation. In addition, we leveraged genetic mutants to gain a molecular understanding of the mechanisms of α-actinin and filamin catch-bonding behavior. Two distinct modes of mechanoaccumulation can be observed: a fast, diffusion-based accumulation and a slower, myosin II-dependent cortical flow phase that acts on proteins with specific binding lifetimes. Finally, we uncovered cell-type- and cell-cycle-stage-specific control of the mechanosensation of myosin IIB, but not myosin IIA or IIC. Overall, these mechanoaccumulative mechanisms drive the cell's response to physical perturbation during proper tissue development and disease.
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9
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Bandi S, Singh SM, Mallela KMG. Interdomain Linker Determines Primarily the Structural Stability of Dystrophin and Utrophin Tandem Calponin-Homology Domains Rather than Their Actin-Binding Affinity. Biochemistry 2015; 54:5480-8. [PMID: 26288220 DOI: 10.1021/acs.biochem.5b00741] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Tandem calponin-homology (CH) domains are the most common actin-binding domains in proteins. However, structural principles underlying their function are poorly understood. These tandem domains exist in multiple conformations with varying degrees of inter-CH-domain interactions. Dystrophin and utrophin tandem CH domains share high sequence similarity (∼82%), yet differ in their structural stability and actin-binding affinity. We examined whether the conformational differences between the two tandem CH domains can explain differences in their stability and actin binding. Dystrophin tandem CH domain is more stable by ∼4 kcal/mol than that of utrophin. Individual CH domains of dystrophin and utrophin have identical structures but differ in their relative orientation around the interdomain linker. We swapped the linkers between dystrophin and utrophin tandem CH domains. Dystrophin tandem CH domain with utrophin linker (DUL) has similar stability as that of utrophin tandem CH domain. Utrophin tandem CH domain with dystrophin linker (UDL) has similar stability as that of dystrophin tandem CH domain. Dystrophin tandem CH domain binds to F-actin ∼30 times weaker than that of utrophin. After linker swapping, DUL has twice the binding affinity as that of dystrophin tandem CH domain. Similarly, UDL has half the binding affinity as that of utrophin tandem CH domain. However, changes in binding free energies due to linker swapping are much lower by an order of magnitude compared to the corresponding changes in unfolding free energies. These results indicate that the linker region determines primarily the structural stability of tandem CH domains rather than their actin-binding affinity.
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Affiliation(s)
- Swati Bandi
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, and ‡Program in Structural Biology and Biochemistry, University of Colorado Anschutz Medical Campus , Aurora, Colorado 80045, United States
| | - Surinder M Singh
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, and ‡Program in Structural Biology and Biochemistry, University of Colorado Anschutz Medical Campus , Aurora, Colorado 80045, United States
| | - Krishna M G Mallela
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, and ‡Program in Structural Biology and Biochemistry, University of Colorado Anschutz Medical Campus , Aurora, Colorado 80045, United States
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10
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Singh SM, Bandi S, Shah DD, Armstrong G, Mallela KMG. Missense mutation Lys18Asn in dystrophin that triggers X-linked dilated cardiomyopathy decreases protein stability, increases protein unfolding, and perturbs protein structure, but does not affect protein function. PLoS One 2014; 9:e110439. [PMID: 25340340 PMCID: PMC4207752 DOI: 10.1371/journal.pone.0110439] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2014] [Accepted: 09/15/2014] [Indexed: 11/19/2022] Open
Abstract
Genetic mutations in a vital muscle protein dystrophin trigger X-linked dilated cardiomyopathy (XLDCM). However, disease mechanisms at the fundamental protein level are not understood. Such molecular knowledge is essential for developing therapies for XLDCM. Our main objective is to understand the effect of disease-causing mutations on the structure and function of dystrophin. This study is on a missense mutation K18N. The K18N mutation occurs in the N-terminal actin binding domain (N-ABD). We created and expressed the wild-type (WT) N-ABD and its K18N mutant, and purified to homogeneity. Reversible folding experiments demonstrated that both mutant and WT did not aggregate upon refolding. Mutation did not affect the protein's overall secondary structure, as indicated by no changes in circular dichroism of the protein. However, the mutant is thermodynamically less stable than the WT (denaturant melts), and unfolds faster than the WT (stopped-flow kinetics). Despite having global secondary structure similar to that of the WT, mutant showed significant local structural changes at many amino acids when compared with the WT (heteronuclear NMR experiments). These structural changes indicate that the effect of mutation is propagated over long distances in the protein structure. Contrary to these structural and stability changes, the mutant had no significant effect on the actin-binding function as evident from co-sedimentation and depolymerization assays. These results summarize that the K18N mutation decreases thermodynamic stability, accelerates unfolding, perturbs protein structure, but does not affect the function. Therefore, K18N is a stability defect rather than a functional defect. Decrease in stability and increase in unfolding decrease the net population of dystrophin molecules available for function, which might trigger XLDCM. Consistently, XLDCM patients have decreased levels of dystrophin in cardiac muscle.
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Affiliation(s)
- Surinder M. Singh
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States of America
| | - Swati Bandi
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States of America
| | - Dinen D. Shah
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States of America
| | - Geoffrey Armstrong
- Department of Chemistry and Biochemistry, University of Colorado Boulder, Boulder, Colorado, United States of America
| | - Krishna M. G. Mallela
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States of America
- Program in Structural Biology and Biochemistry, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States of America
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11
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Wein N, Vulin A, Sofia Falzarano M, Al-Khalili Szigyarto C, Maiti B, Findlay A, Heller KN, Uhlén M, Bakthavachalu B, Messina S, Vita G, Passarelli C, Gualandi F, Wilton SD, Rodino-Klapac L, Yang L, Dunn DM, Schoenberg D, Weiss RB, Howard MT, Ferlini A, Flanigan KM. Translation from a DMD exon 5 IRES results in a functional dystrophin isoform that attenuates dystrophinopathy in humans and mice. Nat Med 2014; 20:992-1000. [PMID: 25108525 PMCID: PMC4165597 DOI: 10.1038/nm.3628] [Citation(s) in RCA: 89] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Accepted: 06/05/2014] [Indexed: 12/26/2022]
Abstract
Most mutations that truncate the reading frame of the DMD gene cause loss of dystrophin expression and lead to Duchenne muscular dystrophy. However, amelioration of disease severity has been shown to result from alternative translation initiation beginning in DMD exon 6 that leads to expression of a highly functional N-truncated dystrophin. Here we demonstrate that this isoform results from usage of an internal ribosome entry site (IRES) within exon 5 that is glucocorticoid inducible. We confirmed IRES activity by both peptide sequencing and ribosome profiling in muscle from individuals with minimal symptoms despite the presence of truncating mutations. We generated a truncated reading frame upstream of the IRES by exon skipping, which led to synthesis of a functional N-truncated isoform in both human subject-derived cell lines and in a new DMD mouse model, where expression of the truncated isoform protected muscle from contraction-induced injury and corrected muscle force to the same level as that observed in control mice. These results support a potential therapeutic approach for patients with mutations within the 5' exons of DMD.
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Affiliation(s)
- Nicolas Wein
- The Center for Gene Therapy, Nationwide Children’s Hospital; The Ohio State University, Columbus, Ohio, USA
| | - Adeline Vulin
- The Center for Gene Therapy, Nationwide Children’s Hospital; The Ohio State University, Columbus, Ohio, USA
| | - Maria Sofia Falzarano
- Section of Microbiology and Medical Genetics, Department of Medical Sciences, University of Ferrara, Ferrara, Italy
| | - Christina Al-Khalili Szigyarto
- Department of Proteomics and Nanobiotechnology, School of Biotechnology, KTH-Royal Institute of Technology, Stockholm, Sweden
| | - Baijayanta Maiti
- Department of Neurology, Washington University School of Medicine, St. Louis, Missouri
| | - Andrew Findlay
- The Center for Gene Therapy, Nationwide Children’s Hospital; The Ohio State University, Columbus, Ohio, USA
| | - Kristin N Heller
- The Center for Gene Therapy, Nationwide Children’s Hospital; The Ohio State University, Columbus, Ohio, USA
| | - Mathias Uhlén
- Department of Proteomics and Nanobiotechnology, School of Biotechnology, KTH-Royal Institute of Technology, Stockholm, Sweden
| | - Baskar Bakthavachalu
- Center for RNA Biology and Department of Molecular and Cellular Biochemistry, The Ohio State University, Columbus, Ohio, USA
| | - Sonia Messina
- Department of Neuroscience, University of Messina and Centro Clinico Nemo Sud, Messina, Italy
| | - Giuseppe Vita
- Department of Neuroscience, University of Messina and Centro Clinico Nemo Sud, Messina, Italy
| | | | - Francesca Gualandi
- Section of Microbiology and Medical Genetics, Department of Medical Sciences, University of Ferrara, Ferrara, Italy
| | - Steve D Wilton
- Centre for Comparative Genomics, Murdoch University, Perth, Australia
| | - Louise Rodino-Klapac
- The Center for Gene Therapy, Nationwide Children’s Hospital; The Ohio State University, Columbus, Ohio, USA
- Department of Pediatrics, The Ohio State University, Columbus, Ohio, USA
| | - Lin Yang
- Division of Biomedical Informatics, Department of Computer Science, University of Kentucky Lexington, Kentucky, USA
| | - Diane M. Dunn
- Department of Human Genetics, The University of Utah School of Medicine, Salt Lake City, Utah, USA
| | - Daniel Schoenberg
- Center for RNA Biology and Department of Molecular and Cellular Biochemistry, The Ohio State University, Columbus, Ohio, USA
| | - Robert B. Weiss
- Department of Human Genetics, The University of Utah School of Medicine, Salt Lake City, Utah, USA
| | - Michael T. Howard
- Department of Human Genetics, The University of Utah School of Medicine, Salt Lake City, Utah, USA
| | - Alessandra Ferlini
- Section of Microbiology and Medical Genetics, Department of Medical Sciences, University of Ferrara, Ferrara, Italy
| | - Kevin M. Flanigan
- The Center for Gene Therapy, Nationwide Children’s Hospital; The Ohio State University, Columbus, Ohio, USA
- Department of Pediatrics, The Ohio State University, Columbus, Ohio, USA
- Department of Neurology, The Ohio State University, Columbus, Ohio, USA
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12
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Blunk AD, Akbergenova Y, Cho RW, Lee J, Walldorf U, Xu K, Zhong G, Zhuang X, Littleton JT. Postsynaptic actin regulates active zone spacing and glutamate receptor apposition at the Drosophila neuromuscular junction. Mol Cell Neurosci 2014; 61:241-54. [PMID: 25066865 PMCID: PMC4134997 DOI: 10.1016/j.mcn.2014.07.005] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Revised: 07/14/2014] [Accepted: 07/23/2014] [Indexed: 12/26/2022] Open
Abstract
Synaptic communication requires precise alignment of presynaptic active zones with postsynaptic receptors to enable rapid and efficient neurotransmitter release. How transsynaptic signaling between connected partners organizes this synaptic apparatus is poorly understood. To further define the mechanisms that mediate synapse assembly, we carried out a chemical mutagenesis screen in Drosophila to identify mutants defective in the alignment of active zones with postsynaptic glutamate receptor fields at the larval neuromuscular junction. From this screen we identified a mutation in Actin 57B that disrupted synaptic morphology and presynaptic active zone organization. Actin 57B, one of six actin genes in Drosophila, is expressed within the postsynaptic bodywall musculature. The isolated allele, act(E84K), harbors a point mutation in a highly conserved glutamate residue in subdomain 1 that binds members of the Calponin Homology protein family, including spectrin. Homozygous act(E84K) mutants show impaired alignment and spacing of presynaptic active zones, as well as defects in apposition of active zones to postsynaptic glutamate receptor fields. act(E84K) mutants have disrupted postsynaptic actin networks surrounding presynaptic boutons, with the formation of aberrant actin swirls previously observed following disruption of postsynaptic spectrin. Consistent with a disruption of the postsynaptic actin cytoskeleton, spectrin, adducin and the PSD-95 homolog Discs-Large are all mislocalized in act(E84K) mutants. Genetic interactions between act(E84K) and neurexin mutants suggest that the postsynaptic actin cytoskeleton may function together with the Neurexin-Neuroligin transsynaptic signaling complex to mediate normal synapse development and presynaptic active zone organization.
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Affiliation(s)
- Aline D Blunk
- The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - Yulia Akbergenova
- The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - Richard W Cho
- The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - Jihye Lee
- The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; The Department of Oral Pathology, School of Dentistry, Pusan National University, Republic of Korea
| | - Uwe Walldorf
- Department of Developmental Biology, University of Saarland, Homburg, Saar, Germany
| | - Ke Xu
- Howard Hughes Medical Institute (HHMI), Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, United States
| | - Guisheng Zhong
- Howard Hughes Medical Institute (HHMI), Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, United States
| | - Xiaowei Zhuang
- Howard Hughes Medical Institute (HHMI), Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, United States; Department of Physics, Harvard University, Cambridge, MA 02138, United States
| | - J Troy Littleton
- The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, United States.
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13
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Singh SM, Bandi S, Winder SJ, Mallela KMG. The actin binding affinity of the utrophin tandem calponin-homology domain is primarily determined by its N-terminal domain. Biochemistry 2014; 53:1801-9. [PMID: 24628267 DOI: 10.1021/bi500149q] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The structural determinants of the actin binding function of tandem calponin-homology (CH) domains are poorly understood, particularly the role of individual domains. We determined the actin binding affinity of isolated CH domains from human utrophin and compared them with the affinity of the full-length tandem CH domain. Traditional cosedimentation assays indicate that the C-terminal CH2 domain binds to F-actin much weaker than the full-length tandem CH domain. The N-terminal CH1 domain is less stable and undergoes severe protein aggregation; therefore, traditional actin cosedimentation assays could not be used. To address this, we have developed a folding-upon-binding method. We refolded the CH1 domain from its unfolded state in the presence of F-actin. This results in a competition between actin binding and aggregation. A differential centrifugation technique was used to distinguish actin binding from aggregation. Low-speed centrifugation pelleted CH1 aggregates, but not F-actin or its bound protein. Subsequent high-speed centrifugation resulted in the cosedimentation of bound CH1 along with F-actin. The CH1 domain binds to F-actin with an affinity similar to that of the full-length tandem CH domain, unlike the CH2 domain. The actin binding cooperativity between the two domains was quantitatively calculated from the association constants of the full-length tandem CH domain and its CH domains, and found to be much smaller than the association constant of the CH1 domain alone. These results indicate that the actin binding affinity of the utrophin tandem CH domain is primarily determined by its CH1 domain, when compared to that of its CH2 domain or the cooperativity between the two CH domains.
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Affiliation(s)
- Surinder M Singh
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus , Aurora, Colorado 80045, United States
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14
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The N-terminal actin-binding tandem calponin-homology (CH) domain of dystrophin is in a closed conformation in solution and when bound to F-actin. Biophys J 2013. [PMID: 23199925 DOI: 10.1016/j.bpj.2012.08.066] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Deficiency of the vital muscle protein dystrophin triggers Duchenne/Becker muscular dystrophy, but the structure-function relationship of dystrophin is poorly understood. To date, molecular structures of three dystrophin domains have been determined, of which the N-terminal actin-binding domain (N-ABD or ABD1) is of particular interest. This domain is composed of two calponin-homology (CH) domains, which form an important class of ABDs in muscle proteins. A previously determined x-ray structure indicates that the dystrophin N-ABD is a domain-swapped dimer, with each monomer adopting an extended, open conformation in which the two CH domains do not interact. This structure is controversial because it contradicts functional studies and known structures of similar ABDs from other muscle proteins. Here, we investigated the solution conformation of the dystrophin N-ABD using a very simple and elegant technique of pyrene excimer fluorescence. Using the wild-type protein, which contains two cysteines, and the corresponding single-cysteine mutants, we show that the protein is a monomer in solution and is in a closed conformation in which the two CH domains seem to interact, as observed from the excimer fluorescence of pyrene-labeled wild-type protein. Excimer fluorescence was also observed in its actin-bound form, indicating that the dystrophin N-ABD binds to F-actin in a closed conformation. Comparison of the dystrophin N-ABD conformation with other ABDs indicates that the tandem CH domains in general may be monomeric in solution and predominantly occur in closed conformation, whereas their actin-bound conformations may differ.
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15
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Abstract
The heterotrimeric laminins are a defining component of all basement membranes and self-assemble into a cell-associated network. The three short arms of the cross-shaped laminin molecule form the network nodes, with a strict requirement for one α, one β and one γ arm. The globular domain at the end of the long arm binds to cellular receptors, including integrins, α-dystroglycan, heparan sulfates and sulfated glycolipids. Collateral anchorage of the laminin network is provided by the proteoglycans perlecan and agrin. A second network is then formed by type IV collagen, which interacts with the laminin network through the heparan sulfate chains of perlecan and agrin and additional linkage by nidogen. This maturation of basement membranes becomes essential at later stages of embryo development.
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16
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Suphamungmee W, Nakamura F, Hartwig JH, Lehman W. Electron microscopy and 3D reconstruction reveals filamin Ig domain binding to F-actin. J Mol Biol 2012; 424:248-56. [PMID: 23041423 DOI: 10.1016/j.jmb.2012.09.025] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2012] [Revised: 09/24/2012] [Accepted: 09/28/2012] [Indexed: 11/24/2022]
Abstract
Filamin A (FLNa) is an actin-binding protein that cross-links F-actin into networks of orthogonally branched filaments. FLNa also directs the networks to integrins while responding to mechanochemical signaling pathways. Flexible, 160-nm-long FLNa molecules are tail-to-tail dimers, each subunit of which contains an N-terminal calponin homology (CH)/actin-binding domain connected by a series of 24 immunoglobulin (Ig) repeats to a dimerization site at their C-terminal end. Whereas the contribution of the CH domains to F-actin affinity is weak (apparent K(a)~10(5)), the binding of the intact protein to F-actin is strong (apparent K(a)~10(8)), suggesting involvement of additional parts of the molecule in this association. Indeed, previous results indicate that Ig repeats along FLNa contribute significantly to the strength of the actin filament interaction. In the current study, we used electron microscopy and three-dimensional reconstruction to elucidate the structural basis of the Ig repeat-F-actin binding. We find that FLNa density is clearly delineated in reconstructions of F-actin complexed either with a four-Ig-repeat segment of FLNa containing Ig repeat 10 or with immunoglobulin-like filamin A repeat (IgFLNa)10 alone. The mass attributable to IgFLNa10 lies peripherally along the actin helix over the N-terminus of actin subdomain 1. The IgFLNa10 interaction appears to be specific, since no other individual Ig repeat or fragment of the FLNa molecule examined, besides ones with IgFLNa10 or CH domains, decorated F-actin filaments or were detected in reconstructions. We conclude that the combined interactions of CH domains and the IgFLNa10 repeat provide the binding strength of the whole FLNa molecule and propose a model for the association of IgFLNa10 on actin filaments.
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Affiliation(s)
- Worawit Suphamungmee
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118, USA
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17
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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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18
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Singh SM, Molas JF, Kongari N, Bandi S, Armstrong GS, Winder SJ, Mallela KM. Thermodynamic stability, unfolding kinetics, and aggregation of the N-terminal actin-binding domains of utrophin and dystrophin. Proteins 2012; 80:1377-92. [PMID: 22275054 PMCID: PMC3439503 DOI: 10.1002/prot.24033] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2011] [Revised: 12/21/2011] [Accepted: 01/02/2012] [Indexed: 12/12/2022]
Abstract
Muscular dystrophy (MD) is the most common genetic lethal disorder in children. Mutations in dystrophin trigger the most common form of MD, Duchenne, and its allelic variant Becker MD. Utrophin is the closest homologue and has been shown to compensate for the loss of dystrophin in human disease animal models. However, the structural and functional similarities and differences between utrophin and dystrophin are less understood. Both proteins interact with actin through their N-terminal actin-binding domain (N-ABD). In this study, we examined the thermodynamic stability and aggregation of utrophin N-ABD and compared with that of dystrophin. Our results show that utrophin N-ABD has spectroscopic properties similar to dystrophin N-ABD. However, utrophin N-ABD has decreased denaturant and thermal stability, unfolds faster, and is correspondingly more susceptible to proteolysis, which might account for its decreased in vivo half-life compared to dystrophin. In addition, utrophin N-ABD aggregates to a lesser extent compared with dystrophin N-ABD, contrary to the general behavior of proteins in which decreased stability enhances protein aggregation. Despite these differences in stability and aggregation, both proteins exhibit deleterious effects of mutations. When utrophin N-ABD mutations analogous in position to the dystrophin disease-causing mutations were generated, they behaved similarly to dystrophin mutants in terms of decreased stability and the formation of cross-β aggregates, indicating a possible role for utrophin mutations in disease mechanisms.
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Affiliation(s)
- Surinder M. Singh
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado 80045, USA
| | - Justine F. Molas
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado 80045, USA
| | - Narsimulu Kongari
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado 80045, USA
| | - Swati Bandi
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado 80045, USA
| | - Geoffrey S. Armstrong
- Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, Colorado 80309, USA
| | - Steve J. Winder
- Department of Biomedical Science, University of Sheffield, Western Bank, Sheffield, S10 2TN, UK
| | - Krishna M.G. Mallela
- Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado 80045, USA
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19
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Lehman W, Morgan KG. Structure and dynamics of the actin-based smooth muscle contractile and cytoskeletal apparatus. J Muscle Res Cell Motil 2012; 33:461-9. [PMID: 22311558 DOI: 10.1007/s10974-012-9283-z] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Accepted: 01/16/2012] [Indexed: 01/04/2023]
Abstract
The thin filaments of differentiated smooth muscle cells are composed of actin and tropomyosin isoforms and numerous ancillary actin-binding proteins that assemble together into distinct thin filament classes. These different filament classes are segregated in smooth muscle cells into structurally and functionally separated contractile and cytoskeletal cellular domains. Typically, thin filaments in smooth muscle cells have been considered to be relatively stable structures like those in striated cells. However, recent efforts have shown that smooth muscle thin filaments indeed are dynamic and that remodeling of the actin cytoskeleton, in particular, regulates smooth muscle function. Thus, the cytoskeleton of differentiated smooth muscle cells appears to function midway between that of less dynamic striated muscle cells and that of very plastic proliferative cells such as fibroblasts. Michael and Kate Bárány keenly followed and participated in some of these studies, consistent with their broad interest in actin function and smooth muscle mechanisms. As a way of honoring the memory of these two pioneer members of the muscle research community, we review data on distribution and remodeling of thin filaments in smooth muscle cells, one of the many research topics that intrigued them.
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Affiliation(s)
- William Lehman
- Department of Physiology and Biophysics, Boston University School of Medicine, 72 East Concord Street, Boston, MA 02118, USA.
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20
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Broderick MJF, Bobkov A, Winder SJ. Utrophin ABD binds to F-actin in an open conformation. FEBS Open Bio 2012; 2:6-11. [PMID: 23650574 PMCID: PMC3642092 DOI: 10.1016/j.fob.2012.01.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2012] [Accepted: 01/18/2012] [Indexed: 11/20/2022] Open
Abstract
Structural analyses of actin binding regions comprising tandem calponin homology domains alone and when bound to F-actin have revealed a number of different conformations with calponin homology domains in ‘open’ and ‘closed’ positions. In an attempt to resolve these issues we have examined the properties of the utrophin actin binding domain in open and closed conformations in order to verify the conformation when bound to F-actin. Locking the actin binding domain in a closed conformation using engineered cysteine residues in each calponin homology domain reduced the affinity for F-actin without affecting the stoichiometry furthermore differential scanning calorimetry experiments revealed a reduction in melting temperature on binding to actin. The data suggest the amino-terminal utrophin actin binding domain is in an open conformation in solution and when bound to F-actin.
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Key Words
- ABD, actin binding domain
- Actin binding domain
- CD, circular dichroism
- CH, calponin homology
- Calponin homology domain
- DSC, differential scanning calorimetry
- Differential scanning calorimetry
- Dystrophin
- EM, electron microscopy
- F-actin, filamentous actin
- NTCB, 2-nitro-5-thiocyanobenzoic acid
- SDS-PAGE, sodium dodecyl sulphate poly-acrylamide electrophoresis
- Spectrin
- Tm, melting temperature
- UTR261, utrophin residues 1-261
- α-Actinin
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Affiliation(s)
- Mike J F Broderick
- Department of Biomedical Science, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK ; IBLS, University of Glasgow, Glasgow G12 8QQ, UK
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21
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Tissue expression and actin binding of a novel N-terminal utrophin isoform. J Biomed Biotechnol 2012; 2011:904547. [PMID: 22228988 PMCID: PMC3228681 DOI: 10.1155/2011/904547] [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: 06/01/2011] [Revised: 07/13/2011] [Accepted: 07/14/2011] [Indexed: 11/21/2022] Open
Abstract
Utrophin and dystrophin present two large proteins that link the intracellular actin cytoskeleton to the extracellular matrix via the C-terminal-associated protein complex. Here we describe a novel short N-terminal isoform of utrophin and its protein product in various rat tissues (N-utro, 62 kDa, amino acids 1–539, comprising the actin-binding domain plus the first two spectrin repeats). Using different N-terminal recombinant utrophin fragments, we show that actin binding exhibits pronounced negative cooperativity (affinity constants K1 = ∼5 × 106
and K2 = ∼1 × 105 M−1) and is Ca2+-insensitive. Expression of the different fragments in COS7 cells and in myotubes indicates that the actin-binding domain alone binds exlusively to actin filaments. The recombinant N-utro analogue binds in vitro to actin and in the cells associates to the membranes. The results indicate that N-utro may be responsible for the anchoring of the cortical actin cytoskeleton to the membranes in muscle and other tissues.
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22
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Large-scale opening of utrophin's tandem calponin homology (CH) domains upon actin binding by an induced-fit mechanism. Proc Natl Acad Sci U S A 2011; 108:12729-33. [PMID: 21768337 DOI: 10.1073/pnas.1106453108] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
We have used site-directed spin labeling and pulsed electron paramagnetic resonance to resolve a controversy concerning the structure of the utrophin-actin complex, with implications for the pathophysiology of muscular dystrophy. Utrophin is a homolog of dystrophin, the defective protein in Duchenne and Becker muscular dystrophies, and therapeutic utrophin derivatives are currently being developed. Both proteins have a pair of N-terminal calponin homology (CH) domains that are important for actin binding. Although there is a crystal structure of the utrophin actin-binding domain, electron microscopy of the actin-bound complexes has produced two very different structural models, in which the CH domains are in open or closed conformations. We engineered a pair of labeling sites in the CH domains of utrophin and used dipolar electron-electron resonance to determine the distribution of interdomain distances with high resolution. We found that the two domains are flexibly connected in solution, indicating a dynamic equilibrium between two distinct open structures. Upon actin binding, the two domains become dramatically separated and ordered, indicating a transition to a single open and extended conformation. There is no trace of this open conformation of utrophin in the absence of actin, providing strong support for an induced-fit model of actin binding.
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23
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Nesprins LINC the nucleus and cytoskeleton. Curr Opin Cell Biol 2010; 23:47-54. [PMID: 21177090 DOI: 10.1016/j.ceb.2010.11.006] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2010] [Revised: 11/19/2010] [Accepted: 11/27/2010] [Indexed: 01/08/2023]
Abstract
Like other spectrin repeat proteins, nesprins co-ordinate and maintain cellular architecture by linking membranous organelles to the cytoskeleton. However nuclear envelope (NE) nesprins, uniquely hardwire the nuclear lamina to the cytoskeleton and molecular motors. Emerging evidence suggests that nesprins also form a continuous network linking the plasma membrane to the NE that potentially translates mechanical stimuli into nuclear reorganisation. Surprisingly, this network is also essential for cytoskeletal organisation and its disruption has dramatic effects on nuclear migration, centrosomal positioning, focal adhesion maturation and cell motility. Herein we review recent advances in our understanding of how nesprins couple to various filamentous systems within the cell and emphasise the importance of both KASH and KASH-less nesprin isoforms in these interactions.
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24
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Hild G, Bugyi B, Nyitrai M. Conformational dynamics of actin: effectors and implications for biological function. Cytoskeleton (Hoboken) 2010; 67:609-29. [PMID: 20672362 PMCID: PMC3038201 DOI: 10.1002/cm.20473] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2010] [Accepted: 07/15/2010] [Indexed: 12/30/2022]
Abstract
Actin is a protein abundant in many cell types. Decades of investigations have provided evidence that it has many functions in living cells. The diverse morphology and dynamics of actin structures adapted to versatile cellular functions is established by a large repertoire of actin-binding proteins. The proper interactions with these proteins assume effective molecular adaptations from actin, in which its conformational transitions play essential role. This review attempts to summarise our current knowledge regarding the coupling between the conformational states of actin and its biological function.
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Affiliation(s)
- Gábor Hild
- Department of Biophysics, University of Pécs, Faculty of Medicine, Pécs, Szigeti str. 12, H-7624, Hungary
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25
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Abstract
The dynamic remolding of the actin cytoskeleton is a critical part of most cellular activities, and malfunction of cytoskeletal proteins results in various human diseases. The transition between two forms of actin, monomeric or G-actin and filamentous or F-actin, is tightly regulated in time and space by a large number of signaling, scaffolding and actin-binding proteins (ABPs). New ABPs are constantly being discovered in the post-genomic era. Most of these proteins are modular, integrating actin binding, protein-protein interaction, membrane-binding, and signaling domains. In response to extracellular signals, often mediated by Rho family GTPases, ABPs control different steps of actin cytoskeleton assembly, including filament nucleation, elongation, severing, capping, and depolymerization. This review summarizes structure-function relationships among ABPs in the regulation of actin cytoskeleton assembly.
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Affiliation(s)
- Sung Haeng Lee
- Chosun University School of Medicine, Department of Cellular and Molecular Medicine, Gwangju 501-759, Korea.
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26
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Sawyer GM, Clark AR, Robertson SP, Sutherland-Smith AJ. Disease-associated substitutions in the filamin B actin binding domain confer enhanced actin binding affinity in the absence of major structural disturbance: Insights from the crystal structures of filamin B actin binding domains. J Mol Biol 2009; 390:1030-47. [PMID: 19505475 DOI: 10.1016/j.jmb.2009.06.009] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2009] [Revised: 05/29/2009] [Accepted: 06/03/2009] [Indexed: 10/20/2022]
Abstract
Missense mutations in filamin B (FLNB) are associated with the autosomal dominant atelosteogenesis (AO) and the Larsen group of skeletal malformation disorders. These mutations cluster in particular FLNB protein domains and act in a presumptive gain-of-function mechanism. In contrast the loss-of-function disorder, spondylocarpotarsal synostosis syndrome, is characterised by the complete absence of FLNB. One cluster of AO missense mutations is found within the second of two calponin homology (CH) domains that create a functional actin-binding domain (ABD). This N-terminal ABD is required for filamin F-actin crosslinking activity, a crucial aspect of filamin's role of integrating cell-signalling events with cellular scaffolding and mechanoprotection. This study characterises the wild type FLNB ABD and investigates the effects of two disease-associated mutations on the structure and function of the FLNB ABD that could explain a gain-of-function mechanism for the AO diseases. We have determined high-resolution X-ray crystal structures of the human filamin B wild type ABD, plus W148R and M202V mutants. All three structures display the classic compact monomeric conformation for the ABD with the CH1 and CH2 domains in close contact. The conservation of tertiary structure in the presence of these mutations shows that the compact ABD conformation is stable to the sequence substitutions. In solution the mutant ABDs display reduced melting temperatures (by 6-7 degrees C) as determined by differential scanning fluorimetry. Characterisation of the wild type and mutant ABD F-actin binding activities via co-sedimentation assays shows that the mutant FLNB ABDs have increased F-actin binding affinities, with dissociation constants of 2.0 microM (W148R) and 0.56 microM (M202V), compared to the wild type ABD K(d) of 7.0 microM. The increased F-actin binding affinity of the mutants presents a biochemical mechanism that differentiates the autosomal dominant gain-of-function FLNB disorders from those that arise through the complete loss of FLNB protein.
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Affiliation(s)
- Gregory M Sawyer
- Institute of Molecular BioSciences, Massey University, Palmerston North, New Zealand
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Dystrophin and utrophin have distinct effects on the structural dynamics of actin. Proc Natl Acad Sci U S A 2009; 106:7822-7. [PMID: 19416869 DOI: 10.1073/pnas.0812007106] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have used time-resolved spectroscopy to investigate the structural dynamics of actin interaction with dystrophin and utrophin in relationship to the pathology of muscular dystrophy. Dystrophin and utrophin bind actin in vitro with similar affinities, but the molecular contacts of these two proteins with actin are different. It has been hypothesized that the presence of two low-affinity actin-binding sites in dystrophin allows more elastic response of the actin-dystrophin-sarcolemma linkage to muscle stretches, compared with utrophin, which binds via one contiguous actin-binding domain. We have directly tested this hypothesis by determining the effects of dystrophin and utrophin on the microsecond rotational dynamics of a phosphorescent dye attached to C374 on actin, as detected by transient phosphorescence anisotropy (TPA). Binding of dystrophin or utrophin to actin resulted in significant changes in the TPA decay, increasing the final anisotropy (restricting the rotational amplitude) and decreasing the rotational correlation times (increasing the rotational rates and the torsional flexibility). This paradoxical combination of effects on actin dynamics (decreased amplitude but increased rate) has not been observed for other actin-binding proteins. Thus, when dystrophin or utrophin binds, actin becomes less like cast iron (strong but brittle) and more like steel (stronger and more resilient). At low levels of saturation, the binding of dystrophin and utrophin has similar effects, but at higher levels, utrophin caused much greater restrictions in amplitude and increases in rate. The effects of dystrophin and utrophin on actin dynamics provide molecular insight into the pathology of muscular dystrophy.
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Sjöblom B, Ylänne J, Djinović-Carugo K. Novel structural insights into F-actin-binding and novel functions of calponin homology domains. Curr Opin Struct Biol 2008; 18:702-8. [PMID: 18952167 DOI: 10.1016/j.sbi.2008.10.003] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2008] [Revised: 10/14/2008] [Accepted: 10/14/2008] [Indexed: 12/23/2022]
Abstract
Tandem calponin homology (CH) domains are well-known actin filaments (F-actin) binding motifs. There has been a continuous debate about the details of CH domain-actin interaction, mainly because atomic level structures of F-actin are not available. A recent electron microscopy study has considerably advanced our structural understanding of CH domain:F-actin complex. On the contrary, it has recently also been shown that CH domains can bind other macromolecular systems: two CH domains from separate polypeptides Ncd80, Nuf2 can form a microtubule-binding site, as well as tandem CH domains in the EB1 dimer, while the single C-terminal CH domain of alpha-parvin has been observed to bind to a alpha-helical leucin-aspartate rich motif from paxillin.
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Affiliation(s)
- Björn Sjöblom
- Department for Biomolecular Structural Chemistry, Max F. Perutz Laboratories, University of Vienna, Campus Vienna Biocenter 5, A-1030 Vienna, Austria
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29
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Egelman EH. Problems in fitting high resolution structures into electron microscopic reconstructions. HFSP JOURNAL 2008; 2:324-31. [PMID: 19436497 DOI: 10.2976/1.2992221] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2008] [Indexed: 11/19/2022]
Abstract
Great advances have been made in electron microscopy (EM) over the past decade, with the result that a number of protein complexes have been solved at near-atomic resolution using EM imaging. However, only a limited number of such complexes are expected to have the high degree of internal order needed to achieve this type of resolution. Many other complexes and polymers will be visualized and reconstructed by EM at an intermediate level of resolution, where the polypeptide chain cannot be directly traced. Crystal and nuclear magnetic resonance structures for components or subunits of these higher-order assemblies are frequently available. One of the greatest strengths of EM continues to be the ability to dock high-resolution structures of components into low or intermediate resolution reconstructions of assemblies to build pseudoatomic models for quaternary structure. This review discusses the strengths and limitations of this approach, with particular emphasis on protein polymers. I discuss how limitations in resolution can lead to ambiguities in building models, and these cannot be always be resolved with available data. The use of homology models for quaternary structure are particularly problematic, given accumulating evidence for the divergence of quaternary structures at the same time that tertiary structure can be conserved.
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Affiliation(s)
- Edward H Egelman
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, Virginia 22908-0733
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30
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Lee SH, Weins A, Hayes DB, Pollak MR, Dominguez R. Crystal structure of the actin-binding domain of alpha-actinin-4 Lys255Glu mutant implicated in focal segmental glomerulosclerosis. J Mol Biol 2008; 376:317-24. [PMID: 18164029 PMCID: PMC2255586 DOI: 10.1016/j.jmb.2007.11.084] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2007] [Revised: 11/22/2007] [Accepted: 11/28/2007] [Indexed: 11/28/2022]
Abstract
Mutations in alpha-actinin-4 have been linked to familial focal segmental glomerulosclerosis (FSGS), a common renal disorder in humans, and produce an apparent increase in the actin-binding affinity of alpha-actinin-4 in vitro. One of the mutations, in particular, Lys255Glu, falls in the middle of the actin-binding interface of the actin-binding domain (ABD). The ABD consists of tandem calponin homology (CH) domains (CH1 and CH2). The crystal structures of most ABDs display a compact conformation, characterized by extensive inter-CH interactions. However, the conformation of F-actin-bound ABDs is unsettled. Some electron microscopy studies find that the compact conformation is preserved upon binding to F-actin, whereas other studies suggest that the CHs separate and the ABD becomes extended. The Lys255Glu mutation in CH2 is significant in this regard since it removes a crucial inter-CH interaction with Trp147 of CH1, thought to stabilize the compact conformation. Together, the increased actin-binding affinity and the removal of this important inter-CH contact suggested that the Lys255Glu mutation might facilitate the transition toward the open ABD conformation proposed by some of the electron microscopy studies. However, the crystal structure of the ABD of alpha-actinin-4 Lys255Glu mutant described here displays the canonical compact conformation. Furthermore, the sedimentation coefficients by analytical ultracentrifugation of wild-type and FSGS mutant ABDs (Lys255Glu, Ser262Pro, and Thr259Ile) are nearly identical (2.50+/-0.03 S) and are in good agreement with the theoretical value calculated from the crystal structure (2.382 S), implying that the compact conformation is retained in solution. The absence of a structural change suggests that the compact ABD conformation observed in the majority of the structures is highly stable and is preserved in solution, even in FSGS mutant ABDs.
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Affiliation(s)
- Sung Haeng Lee
- University of Pennsylvania School of Medicine, Department of Physiology, 3700 Hamilton Walk, Philadelphia, PA 19104−6085
| | - Astrid Weins
- Renal and Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - David B. Hayes
- Boston Biomedical Research Institute, 64 Grove Street, Watertown, MA 02472
| | - Martin R. Pollak
- Renal and Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Roberto Dominguez
- University of Pennsylvania School of Medicine, Department of Physiology, 3700 Hamilton Walk, Philadelphia, PA 19104−6085
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31
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High-resolution cryo-EM structure of the F-actin-fimbrin/plastin ABD2 complex. Proc Natl Acad Sci U S A 2008; 105:1494-8. [PMID: 18234857 DOI: 10.1073/pnas.0708667105] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Many actin binding proteins have a modular architecture, and calponin-homology (CH) domains are one such structurally conserved module found in numerous proteins that interact with F-actin. The manner in which CH-domains bind F-actin has been controversial. Using cryo-EM and a single-particle approach to helical reconstruction, we have generated 12-A-resolution maps of F-actin alone and F-actin decorated with a fragment of human fimbrin (L-plastin) containing tandem CH-domains. The high resolution allows an unambiguous fit of the crystal structure of fimbrin into the map. The interaction between fimbrin ABD2 (actin binding domain 2) and F-actin is different from any interaction previously observed or proposed for tandem CH-domain proteins, showing that the structural conservation of the CH-domains does not lead to a conserved mode of interaction with F-actin. Both the stapling of adjacent actin protomers and the additional closure of the nucleotide binding cleft in F-actin when the fimbrin fragment binds may explain how fimbrin can stabilize actin filaments. A mechanism is proposed where ABD1 of fimbrin becomes activated for binding a second actin filament after ABD2 is bound to a first filament, and this can explain how mutations of residues buried in the interface between ABD2 and ABD1 can rescue temperature-sensitive defects in actin.
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32
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Stone MR, O'Neill A, Lovering RM, Strong J, Resneck WG, Reed PW, Toivola DM, Ursitti JA, Omary MB, Bloch RJ. Absence of keratin 19 in mice causes skeletal myopathy with mitochondrial and sarcolemmal reorganization. J Cell Sci 2007; 120:3999-4008. [PMID: 17971417 DOI: 10.1242/jcs.009241] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Intermediate filaments, composed of desmin and of keratins, play important roles in linking contractile elements to each other and to the sarcolemma in striated muscle. We examined the contractile properties and morphology of fast-twitch skeletal muscle from mice lacking keratin 19. Tibialis anterior muscles of keratin-19-null mice showed a small but significant decrease in mean fiber diameter and in the specific force of tetanic contraction, as well as increased plasma creatine kinase levels. Costameres at the sarcolemma of keratin-19-null muscle, visualized with antibodies against spectrin or dystrophin, were disrupted and the sarcolemma was separated from adjacent myofibrils by a large gap in which mitochondria accumulated. The costameric dystrophin-dystroglycan complex, which co-purified with gamma-actin, keratin 8 and keratin 19 from striated muscles of wild-type mice, co-purified with gamma-actin but not keratin 8 in the mutant. Our results suggest that keratin 19 in fast-twitch skeletal muscle helps organize costameres and links them to the contractile apparatus, and that the absence of keratin 19 disrupts these structures, resulting in loss of contractile force, altered distribution of mitochondria and mild myopathy. This is the first demonstration of a mammalian phenotype associated with a genetic perturbation of keratin 19.
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Affiliation(s)
- Michele R Stone
- Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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33
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Slep KC, Vale RD. Structural basis of microtubule plus end tracking by XMAP215, CLIP-170, and EB1. Mol Cell 2007; 27:976-91. [PMID: 17889670 PMCID: PMC2052927 DOI: 10.1016/j.molcel.2007.07.023] [Citation(s) in RCA: 200] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2007] [Revised: 06/27/2007] [Accepted: 07/17/2007] [Indexed: 02/01/2023]
Abstract
Microtubule plus end binding proteins (+TIPs) localize to the dynamic plus ends of microtubules, where they stimulate microtubule growth and recruit signaling molecules. Three main +TIP classes have been identified (XMAP215, EB1, and CLIP-170), but whether they act upon microtubule plus ends through a similar mechanism has not been resolved. Here, we report crystal structures of the tubulin binding domains of XMAP215 (yeast Stu2p and Drosophila Msps), EB1 (yeast Bim1p and human EB1), and CLIP-170 (human), which reveal diverse tubulin binding interfaces. Functional studies, however, reveal a common property that native or artificial dimerization of tubulin binding domains (including chemically induced heterodimers of EB1 and CLIP-170) induces tubulin nucleation/assembly in vitro and, in most cases, plus end tracking in living cells. We propose that +TIPs, although diverse in structure, share a common property of multimerizing tubulin, thus acting as polymerization chaperones that aid in subunit addition to the microtubule plus end.
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Affiliation(s)
- Kevin C Slep
- Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA 94158, USA
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34
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Antolik C, Catino DH, O’Neill AM, Resneck WG, Ursitti JA, Bloch RJ. The actin binding domain of ACF7 binds directly to the tetratricopeptide repeat domains of rapsyn. Neuroscience 2007; 145:56-65. [PMID: 17222516 PMCID: PMC1868462 DOI: 10.1016/j.neuroscience.2006.11.047] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2006] [Revised: 09/01/2006] [Accepted: 11/12/2006] [Indexed: 11/16/2022]
Abstract
Formation of the neuromuscular junction requires the release of agrin from the presynaptic terminal of motor neurons. Clustering of acetylcholine receptors (AChRs) on the postsynaptic sarcolemma is initiated by agrin-dependent activation of the muscle-specific kinase. While the postsynaptic scaffolding protein rapsyn is vital for high density AChR aggregation, little is known about the mechanism through which AChRs are immobilized on the postsynaptic membrane. Ultrastructural and immunohistochemical studies of rat skeletal muscle have suggested that AChRs are anchored to a membrane-associated cytoskeleton that contains spectrin-like proteins and is thus similar to that of the human erythrocyte [Bloch RJ, Bezakova G, Ursitti JA, Zhou D, Pumplin DW (1997) A membrane skeleton that clusters nicotinic acetylcholine receptors in muscle. Soc Gen Physiol Ser 52:177-195]. We are studying a protein of the spectrin superfamily, ACF7 (also known as MACF), as a postsynaptic cytoskeletal component of the neuromuscular junction. ACF7 has multiple cytoskeleton-binding domains, including an N-terminal actin-binding domain that, we postulate, may interact with rapsyn, the scaffolding protein that binds directly to AChRs. To test this hypothesis, we co-expressed fragments of these molecules in cultured fibroblasts and assessed their co-distribution and interaction using confocal microscopy and co-immunoprecipitation. We demonstrate that the actin-binding domain of ACF7 specifically interacts with the tetratricopeptide repeat domains of rapsyn. Furthermore, we show using surface plasmon resonance and blot overlay that the actin-binding domain of ACF7 binds directly to rapsyn. These results suggest that, in mammalian skeletal muscle, AChRs are immobilized in the membrane through rapsyn-mediated anchoring to an ACF7-containing network that in turn is linked to the actin cytoskeleton.
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Affiliation(s)
- Christian Antolik
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
| | - Dawn H. Catino
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
| | - Andrea M. O’Neill
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
| | - Wendy G. Resneck
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
| | - Jeanine A. Ursitti
- University of Maryland Biotechnology Institute, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
| | - Robert J. Bloch
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
- Corresponding author. 655 W. Baltimore St., Baltimore, MD 21201, USA; Tel: +1-410-706-3020; Fax: +1-410-706-8341. E-mail address: (R.J. Bloch)
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35
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Ervasti JM. Dystrophin, its interactions with other proteins, and implications for muscular dystrophy. Biochim Biophys Acta Mol Basis Dis 2006; 1772:108-17. [PMID: 16829057 DOI: 10.1016/j.bbadis.2006.05.010] [Citation(s) in RCA: 220] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2006] [Revised: 05/31/2006] [Accepted: 05/31/2006] [Indexed: 11/27/2022]
Abstract
Duchenne muscular dystrophy is the most prevalent and severe form of human muscular dystrophy. Investigations into the molecular basis for Duchenne muscular dystrophy were greatly facilitated by seminal studies in the 1980s that identified the defective gene and its major protein product, dystrophin. Biochemical studies revealed its tight association with a multi-subunit complex, the so-named dystrophin-glycoprotein complex. Since its description, the dystrophin-glycoprotein complex has emerged as an important structural unit of muscle and also as a critical nexus for understanding a diverse array of muscular dystrophies arising from defects in several distinct genes. The dystrophin homologue utrophin can compensate at the cell/tissue level for dystrophin deficiency, but functions through distinct molecular mechanisms of protein-protein interaction.
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Affiliation(s)
- James M Ervasti
- Department of Physiology, 127 Service Memorial Institute, University of Wisconsin Medical School, 1300 University Avenue, Madison, WI 53706, USA.
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36
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Galkin VE, Orlova A, Fattoum A, Walsh MP, Egelman EH. The CH-domain of calponin does not determine the modes of calponin binding to F-actin. J Mol Biol 2006; 359:478-85. [PMID: 16626733 DOI: 10.1016/j.jmb.2006.03.044] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2006] [Revised: 03/15/2006] [Accepted: 03/20/2006] [Indexed: 11/30/2022]
Abstract
Many actin-binding proteins have been observed to have a modular architecture. One of the most abundant modules is the calponin-homology (CH) domain, found as tandem repeats in proteins that cross-link actin filaments (such as fimbrin, spectrin and alpha-actinin) or link the actin cytoskeleton to intermediate filaments (such as plectin). In proteins such as the eponymous calponin, IQGAP1, and Scp1, a single CH-domain exists, but there has been some controversy over whether this domain binds to actin filaments. A previous three-dimensional reconstruction of the calponin-F-actin complex has led to the conclusion that the visualized portion of calponin bound to actin belongs to its amino-terminal homology (CH) domain. We show, using a calponin fragment lacking the CH-domain, that this domain is not bound to F-actin, and cannot be positioning calponin on F-actin as hypothesized. Further, using classification methods, we show a multiplicity in cooperative modes of binding of calponin to F-actin, similar to what has been observed for other actin-binding proteins such as tropomyosin and cofilin. Our results suggest that the form and function of the structurally conserved CH-domain found in many other actin-binding proteins have diverged. This has broad implications for inferring function from the presence of structurally conserved domains.
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Affiliation(s)
- Vitold E Galkin
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22908-0733, USA
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37
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Borrego-Diaz E, Kerff F, Lee SH, Ferron F, Li Y, Dominguez R. Crystal structure of the actin-binding domain of alpha-actinin 1: evaluating two competing actin-binding models. J Struct Biol 2006; 155:230-8. [PMID: 16698282 DOI: 10.1016/j.jsb.2006.01.013] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2005] [Accepted: 01/29/2006] [Indexed: 11/28/2022]
Abstract
Alpha-actinin belongs to the spectrin family of actin crosslinking and bundling proteins that function as key regulators of cell motility, morphology and adhesion. The actin-binding domain (ABD) of these proteins consists of two consecutive calponin homology (CH) domains. Electron microscopy studies on ABDs appear to support two competing actin-binding models, extended and compact, whereas the crystal structures typically display a compact conformation. We have determined the 1.7A resolution structure of the ABD of alpha-actinin 1, a ubiquitously expressed isoform. The structure displays the classical compact conformation. We evaluated the two binding models by surface conservation analysis. The results show a conserved surface that spans both domains and corresponds to two previously identified actin-binding sites (ABS2 and ABS3). A third, and probably less important site, ABS1, is mostly buried in the compact conformation. However, a thorough examination of existing structures suggests a weak and semi-polar binding interface between the two CHs, leaving open the possibility of domain reorientation or opening. Our results are consistent with a two-step binding mechanism in which the ABD interacts first in the compact form observed in the structures, and then transitions toward a higher affinity state, possibly through minor rearrangement of the domains.
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Affiliation(s)
- Emma Borrego-Diaz
- Boston Biomedical Research Institute, 64 Grove Street, Watertown, MA 02472, USA
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38
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von Nandelstadh P, Grönholm M, Moza M, Lamberg A, Savilahti H, Carpén O. Actin-organising properties of the muscular dystrophy protein myotilin. Exp Cell Res 2005; 310:131-9. [PMID: 16122733 DOI: 10.1016/j.yexcr.2005.06.027] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2004] [Revised: 06/28/2005] [Accepted: 06/29/2005] [Indexed: 12/27/2022]
Abstract
Myotilin is a sarcomeric Z-disc protein that binds F-actin directly and bundles actin filaments, although it does not contain a conventional actin-binding domain. Expression of mutant myotilin leads to sarcomeric alterations in the dominantly inherited limb-girdle muscular dystrophy 1A and in myofibrillar myopathy/desmin-related myopathy. Together, with previous in vitro studies, this indicates that myotilin has an important function in the assembly and maintenance of Z-discs. This study characterises further the interaction between myotilin and actin. Functionally important regions in myotilin were identified by actin pull-down and yeast two-hybrid assays and with a novel strategy that combines in vitro DNA transposition-based peptide insertion mutagenesis with phenotype analysis in yeast cells. The shortest fragment to bind actin was the second Ig domain together with a short C-terminal sequence. Concerted action of the first and second Ig domain was, however, necessary for the functional activity of myotilin, as verified by analysis of transposon mutants, actin binding and phenotypic effect in mammalian cells. Furthermore, the Ig domains flanked with N- and C-terminal regions were needed for actin-bundling, indicating that the mere actin-binding sequence was insufficient for the actin-regulating activity. None of the four known disease-associated mutations altered the actin-organising ability. These results, together with previous studies in titin and kettin, identify the Ig domain as an actin-binding unit.
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Affiliation(s)
- Pernilla von Nandelstadh
- Department of Anatomy and Neuroscience Program, P.O. Box 63, Biomedicum, University of Helsinki, Finland; Department of Pathology, Helsinki University Hospital, 00014 University of Helsinki, Finland
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39
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Röper K, Mao Y, Brown NH. Contribution of sequence variation inDrosophilaactins to their incorporation into actin-based structures in vivo. J Cell Sci 2005; 118:3937-48. [PMID: 16105877 DOI: 10.1242/jcs.02517] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Actin is a highly conserved protein important for many cellular functions including motility, contraction in muscles and intracellular transport. Many eukaryotic genomes encode multiple actin protein isoforms that differ from each other by only a few residues. We addressed whether the sequence differences between actin paralogues in one species affect their ability to integrate into the large variety of structures generated by filamentous actin. We thus ectopically expressed all six Drosophila actins as fusion proteins with green fluorescent protein (GFP) in a variety of embryonic, larval and adult fly tissues. We found that each actin was able to integrate into most actin structures analysed. For example, in contrast to studies in mammalian cells, the two Drosophila cytoplasmic actins were incorporated into muscle sarcomeres. However, there were differences in the efficiency with which each actin was incorporated into specific actin structures. The most striking difference was observed within the Z-lines of the sarcomeres: one actin was specifically excluded and we mapped this feature to one or both of two residues within the C-terminal half of the protein. Thus, in Drosophila, the primary sequence of different actins does affect their ability to incorporate into actin structures, and so specific GFPactins may be used to label certain actin structures particularly well.
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Affiliation(s)
- Katja Röper
- Wellcome Trust/Cancer Research UK Gurdon Institute and Department of Anatomy, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK
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40
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Abstract
Actin participates in more protein-protein interactions than any other known protein, including the interaction of actin with itself to form the helical polymer F-actin. The vast majority of actin-binding proteins (ABPs) can be grouped into conserved families. Only a handful of structures of complexes of actin with ABPs have been determined so far. These structures are starting to reveal how certain ABPs, including gelsolin, vitamin D-binding protein and Wiskott-Aldrich syndrome protein (WASP)-homology domain-2-related proteins, share a common actin-binding motif. It is proposed here that other ABPs, including actin itself, might share this motif, providing a mechanism whereby ABPs and actin compete for a common binding site. Of particular interest is a hydrophobic pocket that mediates important interactions in five of the existing structures of actin complexes. As the pocket remains accessible in F-actin, it is proposed that this pocket represents a primary target for F-actin-binding proteins, such as calponin-homology-related proteins and myosin.
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Affiliation(s)
- Roberto Dominguez
- Boston Biomedical Research Institute, 64 Grove Street, Watertown, MA 02472, USA.
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41
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Stone MR, O'Neill A, Catino D, Bloch RJ. Specific interaction of the actin-binding domain of dystrophin with intermediate filaments containing keratin 19. Mol Biol Cell 2005; 16:4280-93. [PMID: 16000376 PMCID: PMC1196337 DOI: 10.1091/mbc.e05-02-0112] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Cytokeratins 8 and 19 concentrate at costameres of striated muscle and copurify with the dystrophin-glycoprotein complex, perhaps through the interaction of the cytokeratins with the actin-binding domain of dystrophin. We overexpressed dystrophin's actin-binding domain (Dys-ABD), K8 and K19, as well as closely related proteins, in COS-7 cells to assess the basis and specificity of their interaction. Dys-ABD alone associated with actin microfilaments. Expressed with K8 and K19, which form filaments, Dys-ABD associated preferentially with the cytokeratins. This interaction was specific, as the homologous ABD of betaI-spectrin failed to interact with K8/K19 filaments, and Dys-ABD did not associate with desmin or K8/K18 filaments. Studies in COS-7 cells and in vitro showed that Dys-ABD binds directly and specifically to K19. Expressed in muscle fibers in vivo, K19 accumulated in the myoplasm in structures that contained dystrophin and spectrin and disrupted the organization of the sarcolemma. K8 incorporated into sarcomeres, with no effect on the sarcolemma. Our results show that dystrophin interacts through its ABD with K19 specifically and are consistent with the idea that cytokeratins associate with dystrophin at the sarcolemma of striated muscle.
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Affiliation(s)
- Michele R Stone
- Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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42
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Rybakova IN, Ervasti JM. Identification of spectrin-like repeats required for high affinity utrophin-actin interaction. J Biol Chem 2005; 280:23018-23. [PMID: 15826935 DOI: 10.1074/jbc.m502530200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Most studies aimed at characterizing the utrophinactin interaction have focused on the amino-terminal tandem calponin homology domain. However, we recently reported evidence suggesting that spectrin-like repeats of utrophin also participate in binding to actin. Here we expressed several recombinant fragments encoding the utrophin amino-terminal domain alone or in combination with various numbers of spectrin-like repeats. We further quantitatively characterized the actin binding properties of each recombinant utrophin fragment using a high-speed sedimentation assay. To evaluate the capacity of each protein to stabilize actin filaments, we compared the effect of utrophin recombinant fragments and full-length utrophin on 6-propionyl-2-(N,N-dimethylamino)naphthalene actin depolymerization. Our results suggest that, whereas the amino-terminal domain is essential for primary interaction between utrophin and actin, spectrin-like repeats have additive effects on the affinity and stoichiometry of binding. Our data indicate that the amino-terminal domain and first 10 consecutive spectrin-like repeats recapitulate the actin binding activity of full-length utrophin more faithfully than the amino-terminal domain alone. These findings support the model for lateral association of utrophin along the actin filament and provide the molecular basis for designing the most effective utrophin "mini-genes" for treatment of dystrophinopathies.
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Affiliation(s)
- Inna N Rybakova
- Department of Physiology, University of Wisconsin Medical School, Madison, 53706, USA
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Waheed I, Gilbert R, Nalbantoglu J, Guibinga GH, Petrof BJ, Karpati G. Factors Associated with Induced Chronic Inflammation in mdx Skeletal Muscle Cause Posttranslational Stabilization and Augmentation of Extrasynaptic Sarcolemmal Utrophin. Hum Gene Ther 2005; 16:489-501. [PMID: 15871680 DOI: 10.1089/hum.2005.16.489] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
Chronic inflammation in tibialis anterior muscles of mdx mice was produced by a single injection of a recombinant adenovirus vector (AV) expressing an immunogenic beta-galactosidase (beta-gal). In regions of intense beta-gal staining, mononuclear infiltrates abounded, and muscle fibers showed strong extrasynaptic utrophin immunostaining, restoration of dystrophin-associated protein complex, and a marked reduction of the prevalence of centronucleation. Immunoblot analysis confirmed an increase of endogenous utrophin without an increase of the mRNA of the major muscle isoform utrA. Significantly better maximal tetanic force values were demonstrated in the inflammatory versus control mdx muscles. The resistance to lengthening contraction- induced damage was also significantly increased in the former. In muscles of mice lacking TNF-alpha gene, AV vector did not induce inflammation and extrajunctional utrophin increase did not occur. In the inflammatory mdx muscles, proteolytic activity of calcium-activated calpain was reduced, and in mdx myotubes in vitro, incubation with NO donors also reduced calpain-mediated utrophin proteolysis. Since utrophin was shown to be a natural substrate of calpain and known inhibitors of calpain in cultured mdx myotubes increased utrophin levels, the above results were consistent with the following conclusions: (1) extrasynaptic utrophin increase is mainly responsible for the antidystrophic effect; (2) extrasynaptic utrophin increase is a result of posttranscriptional mechanism(s) related to proinflammatory factors; and (3) reduction of endogenous muscle calpain activity by inflammatory cytokines has an important role in the stabilization and increase of the extrasynaptic utrophin.
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MESH Headings
- Adenoviridae/genetics
- Animals
- Animals, Newborn
- Calcium/metabolism
- Calpain/metabolism
- Cells, Cultured
- Chronic Disease
- Cytokines/genetics
- Cytokines/metabolism
- Male
- Mice
- Mice, Inbred mdx
- Mice, Knockout
- Muscle Fibers, Skeletal/cytology
- Muscle Fibers, Skeletal/drug effects
- Muscle Fibers, Skeletal/metabolism
- Muscle Fibers, Skeletal/pathology
- Muscle, Skeletal/immunology
- Muscle, Skeletal/metabolism
- Muscle, Skeletal/pathology
- Myositis/etiology
- Myositis/metabolism
- Myositis/pathology
- Nitric Oxide Donors/pharmacology
- Protein Processing, Post-Translational
- Sarcolemma/metabolism
- Synapses/metabolism
- Utrophin/drug effects
- Utrophin/genetics
- Utrophin/metabolism
- beta-Galactosidase/adverse effects
- beta-Galactosidase/genetics
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Affiliation(s)
- Ishrat Waheed
- Neuromuscular Research Group, Montreal Neurological Institute, McGill University, Montréal, Québec, Canada, H3A 2B4
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Franzot G, Sjöblom B, Gautel M, Djinović Carugo K. The Crystal Structure of the Actin Binding Domain from α-Actinin in its Closed Conformation: Structural Insight into Phospholipid Regulation of α-Actinin. J Mol Biol 2005; 348:151-65. [PMID: 15808860 DOI: 10.1016/j.jmb.2005.01.002] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2004] [Revised: 12/22/2004] [Accepted: 01/03/2005] [Indexed: 10/25/2022]
Abstract
Alpha-actinin is the major F-actin crosslinking protein in both muscle and non-muscle cells. We report the crystal structure of the actin binding domain of human muscle alpha-actinin-3, which is formed by two consecutive calponin homology domains arranged in a "closed" conformation. Structural studies and available biochemical data on actin binding domains suggest that two calponin homology domains come in a closed conformation in the native apo-form, and that conformational changes involving the relative orientation of the two calponin homology domains are required for efficient binding to actin filaments. The actin binding activity of muscle isoforms is supposed to be regulated by phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2), which binds to the second calponin homology domain. On the basis of structural analysis we propose a distinct binding site for PtdIns(4,5)P2, where the fatty acid moiety would be oriented in a direction that allows it to interact with the linker sequence between the actin binding domain and the first spectrin-like repeat, regulating thereby the binding of the C-terminal calmodulin-like domain to this linker.
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Affiliation(s)
- Giacomo Franzot
- Structural Biology Laboratory, Elettra-Sincrotrone Trieste in Area Science Park, S.S. 14 Km 163,5 34012 Trieste, Italy
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Hodgkinson JL, Peters C, Kuznetsov SA, Steffen W. Three-dimensional reconstruction of the dynactin complex by single-particle image analysis. Proc Natl Acad Sci U S A 2005; 102:3667-72. [PMID: 15738427 PMCID: PMC553325 DOI: 10.1073/pnas.0409506102] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2004] [Accepted: 01/20/2005] [Indexed: 11/18/2022] Open
Abstract
Dynactin is a large complex of at least nine distinct proteins that co-complexes with cytoplasmic dynein within cells, where it plays a major role as a regulator of the motor's function. Owing to its large size and complexity, relatively little is known about dynactin's 3D structure or the structural basis of its function. Use of single-particle image analysis techniques has enabled us to produce the first 3D reconstruction of the dynactin complex, to a resolution of 3 nm. The actin-related protein (Arp) backbone of the filament has been clearly visualized. Fitting of models of the Arp backbone showed that it consists of 10 subunits. Additional mass, not part of the Arp backbone, was also seen. A preliminary fitting of the capping protein CapZ structure into our 3D reconstruction of the dynactin complex suggests that it is optimally placed to perform its proposed function as a stabilizer of the Arp1 backbone and gives clues as to likely interaction points between the capping protein and Arp subunits. The results provide the first detailed visualization of the dynactin complex and shed light on the mode of interaction between several of its constituent proteins and their possible functions.
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Affiliation(s)
- J L Hodgkinson
- Department of Biomedical Sciences, Imperial College London, London SW3 6LY, United Kingdom
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Abstract
Spectrin family proteins represent an important group of actin-bundling and membrane-anchoring proteins found in diverse structures from yeast to man. Arising from a common ancestral alpha-actinin gene through duplications and rearrangements, the family has increased to include the spectrins and dystrophin/utrophin. The spectrin family is characterized by the presence of spectrin repeats, actin binding domains, and EF hands. With increasing divergence, new domains and functions have been added such that spectrin and dystrophin also contain specialized protein-protein interaction motifs and regions for interaction with membranes and phospholipids. The acquisition of new domains also increased the functional complexity of the family such that the proteins perform a range of tasks way beyond the simple bundling of actin filaments by alpha-actinin in S. pombe. We discuss the evolutionary, structural, functional, and regulatory roles of the spectrin family of proteins and describe some of the disease traits associated with loss of spectrin family protein function.
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Affiliation(s)
- M J F Broderick
- Department of Biomedical Science, University of Sheffield, Sheffield S10 2TN, United Kingdom
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Lee HS, Bellin RM, Walker DL, Patel B, Powers P, Liu H, Garcia-Alvarez B, de Pereda JM, Liddington RC, Volkmann N, Hanein D, Critchley DR, Robson RM. Characterization of an actin-binding site within the talin FERM domain. J Mol Biol 2004; 343:771-84. [PMID: 15465061 DOI: 10.1016/j.jmb.2004.08.069] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2004] [Revised: 08/10/2004] [Accepted: 08/16/2004] [Indexed: 11/24/2022]
Abstract
Talin is a large cytoskeletal protein that couples integrins to F-actin. Three actin-binding sites (ABS1-3) have been reported: one in the N-terminal head, and two in the C-terminal rod domain. Although the C-terminal ABS3 has been partially characterized, the presence and properties of ABS1 within the talin head are less well defined. We show here that the talin head binds F-actin in vitro and in vivo at a specific site within the actin filament. Thus, purified talin head liberated from gizzard talin by calpain cleavage cosediments with F-actin in a low salt buffer at pH 6.4 (conditions that are optimal for binding intact talin), and using recombinant polypeptides, we have mapped ABS1 to the FERM domain within the talin head. Both the F2 and F3 FERM subdomains contribute to binding, and EGFP-tagged FERM subdomains colocalize with actin stress fibers when expressed in COS cells. High-resolution electron microscopy of actin filaments decorated with F2F3 localizes binding to a site that is distinct from that recognized by members of the calponin-homology superfamily. Finally, we show that the FERM domain can couple F-actin to PIPkin, and by inference to integrins, since they bind to the same pocket in the F3 subdomain. This suggests that the talin FERM domain functions as a linker between PIPkin or integrins and F-actin at sites of cell-matrix adhesions.
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Affiliation(s)
- Ho-Sup Lee
- Muscle Biology Group, Departments of Biochemistry, Biophysics, and Molecular Biology and of Animal Science, Iowa State University, Ames, IA 50011-3260, USA
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Yang S, Yu X, Galkin VE, Egelman EH. Issues of resolution and polymorphism in single-particle reconstruction. J Struct Biol 2004; 144:162-71. [PMID: 14643219 DOI: 10.1016/j.jsb.2003.09.016] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Three-dimensional reconstruction from electron microscopic (EM) images of isolated macromolecular complexes is being employed by many laboratories. This approach is extremely powerful and continues to improve in resolution. In the absence of stereochemical constraints that can be used to assess the quality of a reconstruction, as exist in X-ray crystallography, several other measures have typically been used. A very useful assessment of quality can be made in the comparison between the projections of the three-dimensional reconstruction and averages generated from classes of images. The main quantitative measure has been that of resolution statistics, typically based upon Fourier shell correlations. We show, using only simulated noise for images, that impressive resolution statistics are generated that can even extend the apparent resolution of the starting model. When truly independent reconstructions are generated starting from different initial models, however, such artefacts are not possible. We also show, using real images of DnaB rings, that in the presence of polymorphism artefactual reconstructions can be generated whose projections match class averages. These averages, however, are themselves artefactual as they involve heterogeneous images. The issues presented here need to be considered when single-particle EM reconstructions are evaluated.
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Affiliation(s)
- Shixin Yang
- Department of Biochemistry and Molecular Genetics, University of Virginia Health Sciences Center, Charlottesville, VA 22908-0733, USA
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Sevcík J, Urbániková L, Kost'an J, Janda L, Wiche G. Actin-binding domain of mouse plectin. Crystal structure and binding to vimentin. ACTA ACUST UNITED AC 2004; 271:1873-84. [PMID: 15128297 DOI: 10.1111/j.1432-1033.2004.04095.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Plectin, a large and widely expressed cytolinker protein, is composed of several subdomains that harbor binding sites for a variety of different interaction partners. A canonical actin-binding domain (ABD) comprising two calponin homology domains (CH1 and CH2) is located in proximity to its amino terminus. However, the ABD of plectin is unique among actin-binding proteins as it is expressed in the form of distinct, plectin isoform-specific versions. We have determined the three-dimensional structure of two distinct crystalline forms of one of its ABD versions (pleABD/2alpha) from mouse, to a resolution of 1.95 and 2.0 A. Comparison of pleABD/2alpha with the ABDs of fimbrin and utrophin revealed structural similarity between plectin and fimbrin, although the proteins share only low sequence identity. In fact, pleABD/2alpha has been found to have the same compact fold as the human plectin ABD and the fimbrin ABD, differing from the open conformation described for the ABDs of utrophin and dystrophin. Plectin harbors a specific binding site for intermediate filaments of various types within its carboxy-terminal R5 repeat domain. Our experiments revealed an additional vimentin-binding site of plectin, residing within the CH1 subdomain of its ABD. We show that vimentin binds to this site via the amino-terminal part of its rod domain. This additional amino-terminal intermediate filament protein binding site of plectin may have a function in intermediate filament dynamics and assembly, rather than in linking and stabilizing intermediate filament networks.
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Affiliation(s)
- Jozef Sevcík
- Institute of Molecular Biology, Slovak Academy of Sciences, Bratislava, Slovak Republic
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