1
|
Douglas CM, Bird JE, Kopinke D, Esser KA. An optimized approach to study nanoscale sarcomere structure utilizing super-resolution microscopy with nanobodies. PLoS One 2024; 19:e0300348. [PMID: 38687705 PMCID: PMC11060602 DOI: 10.1371/journal.pone.0300348] [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: 11/06/2023] [Accepted: 02/23/2024] [Indexed: 05/02/2024] Open
Abstract
The sarcomere is the fundamental contractile unit in skeletal muscle, and the regularity of its structure is critical for function. Emerging data demonstrates that nanoscale changes to the regularity of sarcomere structure can affect the overall function of the protein dense ~2μm sarcomere. Further, sarcomere structure is implicated in many clinical conditions of muscle weakness. However, our understanding of how sarcomere structure changes in disease, especially at the nanoscale, has been limited in part due to the inability to robustly detect and measure at sub-sarcomere resolution. We optimized several methodological steps and developed a robust pipeline to analyze sarcomere structure using structured illumination super-resolution microscopy in conjunction with commercially-available and fluorescently-conjugated Variable Heavy-Chain only fragment secondary antibodies (nanobodies), and achieved a significant increase in resolution of z-disc width (353nm vs. 62nm) compared to confocal microscopy. The combination of these methods provides a unique approach to probe sarcomere protein localization at the nanoscale and may prove advantageous for analysis of other cellular structures.
Collapse
Affiliation(s)
- Collin M. Douglas
- Department of Physiology and Aging, University of Florida, Gainesville, Florida, United States of America
| | - Jonathan E. Bird
- Department of Pharmacology and Therapeutics, University of Florida, Gainesville, Florida, United States of America
| | - Daniel Kopinke
- Department of Pharmacology and Therapeutics, University of Florida, Gainesville, Florida, United States of America
| | - Karyn A. Esser
- Department of Physiology and Aging, University of Florida, Gainesville, Florida, United States of America
| |
Collapse
|
2
|
Noureddine M, Gehmlich K. Structural and signaling proteins in the Z-disk and their role in cardiomyopathies. Front Physiol 2023; 14:1143858. [PMID: 36935760 PMCID: PMC10017460 DOI: 10.3389/fphys.2023.1143858] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2023] [Accepted: 02/21/2023] [Indexed: 03/06/2023] Open
Abstract
The sarcomere is the smallest functional unit of muscle contraction. It is delineated by a protein-rich structure known as the Z-disk, alternating with M-bands. The Z-disk anchors the actin-rich thin filaments and plays a crucial role in maintaining the mechanical stability of the cardiac muscle. A multitude of proteins interact with each other at the Z-disk and they regulate the mechanical properties of the thin filaments. Over the past 2 decades, the role of the Z-disk in cardiac muscle contraction has been assessed widely, however, the impact of genetic variants in Z-disk proteins has still not been fully elucidated. This review discusses the various Z-disk proteins (alpha-actinin, filamin C, titin, muscle LIM protein, telethonin, myopalladin, nebulette, and nexilin) and Z-disk-associated proteins (desmin, and obscurin) and their role in cardiac structural stability and intracellular signaling. This review further explores how genetic variants of Z-disk proteins are linked to inherited cardiac conditions termed cardiomyopathies.
Collapse
Affiliation(s)
- Maya Noureddine
- Institute of Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham, United Kingdom
- *Correspondence: Maya Noureddine, ; Katja Gehmlich,
| | - Katja Gehmlich
- Institute of Cardiovascular Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham, United Kingdom
- Cardiovascular Medicine, Radcliffe Department of Medicine and British Heart Foundation Centre of Research Excellence Oxford, University of Oxford, Oxford, United Kingdom
- *Correspondence: Maya Noureddine, ; Katja Gehmlich,
| |
Collapse
|
3
|
Ahmad MN, Mat Noh NA, Abdullah EN, Yarmo MA, Mat Piah MB, Ku Bulat KH. Optimization of a protease extraction using a statistical approach for the production of an alternative meat tenderizer fromSpondias cytherearoots. J FOOD PROCESS PRES 2019. [DOI: 10.1111/jfpp.14192] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Mohammad Norazmi Ahmad
- Experimental and Theoretical Research Laboratory Department of Chemistry Kulliyyah of Science, International Islamic University Malaysia Kuantan Malaysia
| | - Nor Aini Mat Noh
- Experimental and Theoretical Research Laboratory Department of Chemistry Kulliyyah of Science, International Islamic University Malaysia Kuantan Malaysia
| | - Erna Normaya Abdullah
- Experimental and Theoretical Research Laboratory Department of Chemistry Kulliyyah of Science, International Islamic University Malaysia Kuantan Malaysia
| | - Mohd Ambar Yarmo
- School of Chemical Sciences and Food Technology Faculty of Science and Technology Universiti Kebangsaan Malaysia Bangi Malaysia
| | - Mohd Bijarimi Mat Piah
- Faculty of Chemical & Natural Resources Engineering Universiti Malaysia Pahang Kuantan Malaysia
| | - Ku Halim Ku Bulat
- Department of Chemistry, Faculty of Science University Malaysia Terengganu Kuala Terengganu Malaysia
| |
Collapse
|
4
|
Villalobo A, González-Muñoz M, Berchtold MW. Proteins with calmodulin-like domains: structures and functional roles. Cell Mol Life Sci 2019; 76:2299-2328. [PMID: 30877334 PMCID: PMC11105222 DOI: 10.1007/s00018-019-03062-z] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2018] [Revised: 02/26/2019] [Accepted: 03/07/2019] [Indexed: 12/21/2022]
Abstract
The appearance of modular proteins is a widespread phenomenon during the evolution of proteins. The combinatorial arrangement of different functional and/or structural domains within a single polypeptide chain yields a wide variety of activities and regulatory properties to the modular proteins. In this review, we will discuss proteins, that in addition to their catalytic, transport, structure, localization or adaptor functions, also have segments resembling the helix-loop-helix EF-hand motifs found in Ca2+-binding proteins, such as calmodulin (CaM). These segments are denoted CaM-like domains (CaM-LDs) and play a regulatory role, making these CaM-like proteins sensitive to Ca2+ transients within the cell, and hence are able to transduce the Ca2+ signal leading to specific cellular responses. Importantly, this arrangement allows to this group of proteins direct regulation independent of other Ca2+-sensitive sensor/transducer proteins, such as CaM. In addition, this review also covers CaM-binding proteins, in which their CaM-binding site (CBS), in the absence of CaM, is proposed to interact with other segments of the same protein denoted CaM-like binding site (CLBS). CLBS are important regulatory motifs, acting either by keeping these CaM-binding proteins inactive in the absence of CaM, enhancing the stability of protein complexes and/or facilitating their dimerization via CBS/CLBS interaction. The existence of proteins containing CaM-LDs or CLBSs substantially adds to the enormous versatility and complexity of Ca2+/CaM signaling.
Collapse
Affiliation(s)
- Antonio Villalobo
- Department of Cancer Biology, Instituto de Investigaciones Biomédicas, Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid, Arturo Duperier 4, 28029, Madrid, Spain.
- Instituto de Investigaciones Sanitarias, Hospital Universitario La Paz, Edificio IdiPAZ, Paseo de la Castellana 261, 28046, Madrid, Spain.
| | - María González-Muñoz
- Department of Cancer Biology, Instituto de Investigaciones Biomédicas, Consejo Superior de Investigaciones Científicas and Universidad Autónoma de Madrid, Arturo Duperier 4, 28029, Madrid, Spain
| | - Martin W Berchtold
- Department of Biology, University of Copenhagen, 13 Universitetsparken, 2100, Copenhagen, Denmark.
| |
Collapse
|
5
|
Sun X, Liu Z, Wu B, Zhou L, Wang Q, Wu W, Yang A. Differences between fast and slow muscles in scallops revealed through proteomics and transcriptomics. BMC Genomics 2018; 19:377. [PMID: 29783952 PMCID: PMC5963113 DOI: 10.1186/s12864-018-4770-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Accepted: 05/09/2018] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Scallops possess striated and catch adductor muscles, which have different structure and contractile properties. The striated muscle contracts very quickly for swimming, whereas the smooth catch muscle can keep the shells closed for long periods with little expenditure of energy. In this study, we performed proteomic and transcriptomic analyses of differences between the striated (fast) and catch (slow) adductor muscles in Yesso scallop Patinopecten yessoensis. RESULTS Transcriptomic analysis reveals 1316 upregulated and 8239 downregulated genes in slow compared to fast adductor muscle. For the same comparison, iTRAQ-based proteomics reveals 474 differentially expressed proteins (DEPs), 198 up- and 276 downregulated. These DEPs mainly comprise muscle-specific proteins of the sarcoplasmic reticulum, extracellular matrix, and metabolic pathways. A group of conventional muscle proteins-myosin heavy chain, myosin regulatory light chain, myosin essential light chain, and troponin-are enriched in fast muscle. In contrast, paramyosin, twitchin, and catchin are preferentially expressed in slow muscle. The association analysis of proteomic and transcriptomic data provides the evidences of regulatory events at the transcriptional and posttranscriptional levels in fast and slow muscles. Among 1236 differentially expressed unigenes, 22.7% show a similar regulation of mRNA levels and protein abundances. In contrast, more unigenes (53.2%) exhibit striking differences between gene expression and protein abundances in the two muscles, which indicates the existence of fiber-type specific, posttranscriptional regulatory events in most of myofibrillar proteins, such as myosin heavy chain, titin, troponin, and twitchin. CONCLUSIONS This first, global view of protein and mRNA expression levels in scallop fast and slow muscles reveal that regulatory mechanisms at the transcriptional and posttranscriptional levels are essential in the maintenance of muscle structure and function. The existence of fiber-type specific, posttranscriptional regulatory mechanisms in myofibrillar proteins will greatly improve our understanding of the molecular basis of muscle contraction and its regulation in non-model invertebrates.
Collapse
Affiliation(s)
- Xiujun Sun
- Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao, 266071, China.,Function Laboratory for Marine Fisheries Science and Food Production Processes, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266200, People's Republic of China
| | - Zhihong Liu
- Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao, 266071, China.,Function Laboratory for Marine Fisheries Science and Food Production Processes, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266200, People's Republic of China
| | - Biao Wu
- Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao, 266071, China.,Function Laboratory for Marine Fisheries Science and Food Production Processes, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266200, People's Republic of China
| | - Liqing Zhou
- Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao, 266071, China.,Function Laboratory for Marine Fisheries Science and Food Production Processes, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266200, People's Republic of China
| | - Qi Wang
- College of Fisheries, Ocean University of China, Qingdao, 266003, China
| | - Wei Wu
- Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao, 266071, China.,Function Laboratory for Marine Fisheries Science and Food Production Processes, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266200, People's Republic of China
| | - Aiguo Yang
- Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao, 266071, China. .,Function Laboratory for Marine Fisheries Science and Food Production Processes, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266200, People's Republic of China.
| |
Collapse
|
6
|
Schilling MW, Suman SP, Zhang X, Nair MN, Desai MA, Cai K, Ciaramella MA, Allen PJ. Proteomic approach to characterize biochemistry of meat quality defects. Meat Sci 2017; 132:131-138. [PMID: 28454727 DOI: 10.1016/j.meatsci.2017.04.018] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Revised: 04/19/2017] [Accepted: 04/19/2017] [Indexed: 02/06/2023]
Abstract
Proteomics can be used to characterize quality defects including pale, soft, and exudative (PSE) meat (pork and poultry), woody broiler breast meat, reddish catfish fillets, meat toughness, and beef myoglobin oxidation. PSE broiler meat was characterized by 15 proteins that differed in abundance in comparison to normal broiler breast meat, and eight proteins were differentially expressed in woody breast meat in comparison to normal breast meat. Hemoglobin was the only protein that was differentially expressed between red and normal catfish fillets. However, inducing low oxygen and/or heat stress conditions to catfish fillets did not lead to the production of red fillets. Proteomic data provided information pertaining to the protein differences that exist in meat quality defects. However, these data need to be evaluated in conjunction with information pertaining to genetics, nutrition, environment of the live animal, muscle to meat conversion, meat quality analyses and sensory attributes to understand causality, protein biomarkers, and ultimately how to prevent quality defects.
Collapse
Affiliation(s)
- M W Schilling
- Department of Food Science, Nutrition and Health Promotion, Mississippi State University, Mississippi State, MS 39762, United States.
| | - S P Suman
- Department of Animal and Food Sciences, University of Kentucky, Lexington, KY 40546, United States
| | - X Zhang
- Department of Food Science, Nutrition and Health Promotion, Mississippi State University, Mississippi State, MS 39762, United States
| | - M N Nair
- Department of Animal and Food Sciences, University of Kentucky, Lexington, KY 40546, United States
| | - M A Desai
- Reed Food Technology, Pearl, MS 39208, United States
| | - K Cai
- Department of Food Science, Nutrition and Health Promotion, Mississippi State University, Mississippi State, MS 39762, United States
| | - M A Ciaramella
- New York Sea Grant, College of Agriculture and Life Sciences, Cornell University, Stony Brook, NY 11794, United States
| | - P J Allen
- Department of Wildlife, Fisheries, and Aquaculture, Mississippi State University, Mississippi State, MS 39762, United States
| |
Collapse
|
7
|
Ciaramella MA, Nair MN, Suman SP, Allen PJ, Schilling MW. Differential abundance of muscle proteome in cultured channel catfish (Ictalurus punctatus) subjected to ante-mortem stressors and its impact on fillet quality. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. PART D, GENOMICS & PROTEOMICS 2016; 20:10-18. [PMID: 27484844 DOI: 10.1016/j.cbd.2016.06.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Revised: 06/10/2016] [Accepted: 06/23/2016] [Indexed: 11/19/2022]
Abstract
The effects of environmental and handling stress during catfish (Ictalurus punctatus) aquaculture were evaluated to identify the biochemical alterations they induce in the muscle proteome and their impacts on fillet quality. Temperature (25°C and 33°C) and oxygen (~2.5mg/L [L] and >5mg/L [H]) were manipulated followed by sequential socking (S) and transport (T) stress to evaluate changes in quality when fish were subjected to handling (25-H-ST; temperature-oxygen-handling), oxygen stress (25-L-ST), temperature stress (33-H-ST) and severe stress (33-L-ST). Instrumental color and texture of fillets were evaluated, and muscle proteome profile was analyzed. Fillet redness, yellowness and chroma decreased, and hue angle increased in all treatments except temperature stress (33-H-ST). Alterations in texture compared to controls were observed when oxygen levels were held high. In general, changes in the abundance of structural proteins and those involved in protein regulation and energy metabolism were identified. Rearing under hypoxic conditions demonstrated a shift in metabolism to ketogenic pathways and a suppression of the stress-induced changes as the severity of the stress increased. Increased proteolytic activity observed through the down-regulation of various structural proteins could be responsible for the alterations in color and texture.
Collapse
Affiliation(s)
- Michael A Ciaramella
- Mississippi State University, Department of Food Science, Nutrition and Health Promotion, Herzer Building, 945 Stone Blvd, Box 9805, Mississippi State, MS 39762, United States; Mississippi State University, Department Wildlife, Fisheries and Aquaculture, Box 9690, Mississippi State, MS 39762, United States.
| | - Mahesh N Nair
- University of Kentucky, Department of Animal and Food Sciences, Lexington, KY 40546, United States
| | - Surendranath P Suman
- University of Kentucky, Department of Animal and Food Sciences, Lexington, KY 40546, United States.
| | - Peter J Allen
- Mississippi State University, Department Wildlife, Fisheries and Aquaculture, Box 9690, Mississippi State, MS 39762, United States.
| | - M Wes Schilling
- Mississippi State University, Department of Food Science, Nutrition and Health Promotion, Herzer Building, 945 Stone Blvd, Box 9805, Mississippi State, MS 39762, United States.
| |
Collapse
|
8
|
Gautel M, Djinović-Carugo K. The sarcomeric cytoskeleton: from molecules to motion. ACTA ACUST UNITED AC 2016; 219:135-45. [PMID: 26792323 DOI: 10.1242/jeb.124941] [Citation(s) in RCA: 143] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Highly ordered organisation of striated muscle is the prerequisite for the fast and unidirectional development of force and motion during heart and skeletal muscle contraction. A group of proteins, summarised as the sarcomeric cytoskeleton, is essential for the ordered assembly of actin and myosin filaments into sarcomeres, by combining architectural, mechanical and signalling functions. This review discusses recent cell biological, biophysical and structural insight into the regulated assembly of sarcomeric cytoskeleton proteins and their roles in dissipating mechanical forces in order to maintain sarcomere integrity during passive extension and active contraction. α-Actinin crosslinks in the Z-disk show a pivot-and-rod structure that anchors both titin and actin filaments. In contrast, the myosin crosslinks formed by myomesin in the M-band are of a ball-and-spring type and may be crucial in providing stable yet elastic connections during active contractions, especially eccentric exercise.
Collapse
Affiliation(s)
- Mathias Gautel
- King's College London BHF Centre of Research Excellence, Randall Division for Cell and Molecular Biophysics, and Cardiovascular Division, New Hunt's House, London SE1 1UL, UK
| | - Kristina Djinović-Carugo
- Department of Structural and Computational Biology, Max F. Perutz Laboratories, University of Vienna, Campus Vienna Biocenter 5, Vienna A-1030, Austria Department of Biochemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, Ljubljana 1000, Slovenia
| |
Collapse
|
9
|
Fan X, Hughes BG, Ali MAM, Cho WJ, Lopez W, Schulz R. Dynamic Alterations to α-Actinin Accompanying Sarcomere Disassembly and Reassembly during Cardiomyocyte Mitosis. PLoS One 2015; 10:e0129176. [PMID: 26076379 PMCID: PMC4467976 DOI: 10.1371/journal.pone.0129176] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Accepted: 05/05/2015] [Indexed: 11/19/2022] Open
Abstract
Although mammals are thought to lose their capacity to regenerate heart muscle shortly after birth, embryonic and neonatal cardiomyocytes in mammals are hyperplastic. During proliferation these cells need to selectively disassemble their myofibrils for successful cytokinesis. The mechanism of sarcomere disassembly is, however, not understood. To study this, we performed a series of immunofluorescence studies of multiple sarcomeric proteins in proliferating neonatal rat ventricular myocytes and correlated these observations with biochemical changes at different cell cycle stages. During myocyte mitosis, α-actinin and titin were disassembled as early as prometaphase. α-actinin (representing the sarcomeric Z-disk) disassembly precedes that of titin (M-line), suggesting that titin disassembly occurs secondary to the collapse of the Z-disk. Sarcomere disassembly was concurrent with the dissolution of the nuclear envelope. Inhibitors of several intracellular proteases could not block the disassembly of α-actinin or titin. There was a dramatic increase in both cytosolic (soluble) and sarcomeric α-actinin during mitosis, and cytosolic α-actinin exhibited decreased phosphorylation compared to sarcomeric α-actinin. Inhibition of cyclin-dependent kinase 1 (CDK1) induced the quick reassembly of the sarcomere. Sarcomere dis- and re-assembly in cardiomyocyte mitosis is CDK1-dependent and features dynamic differential post-translational modifications of sarcomeric and cytosolic α-actinin.
Collapse
Affiliation(s)
- Xiaohu Fan
- Department of Pediatrics, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
- Department of Pharmacology, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
- Cardiovascular Research Centre, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
- Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Bryan G. Hughes
- Department of Pediatrics, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
- Department of Pharmacology, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
- Cardiovascular Research Centre, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
- Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Mohammad A. M. Ali
- Department of Pediatrics, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
- Department of Pharmacology, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
- Cardiovascular Research Centre, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
- Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Woo Jung Cho
- Department of Medical Microbiology & Immunology, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
| | - Waleska Lopez
- Department of Pediatrics, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
- Department of Pharmacology, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
- Cardiovascular Research Centre, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
- Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Richard Schulz
- Department of Pediatrics, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
- Department of Pharmacology, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
- Cardiovascular Research Centre, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, Alberta, Canada
- Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada
- * E-mail:
| |
Collapse
|
10
|
Sequeira V, Nijenkamp LLAM, Regan JA, van der Velden J. The physiological role of cardiac cytoskeleton and its alterations in heart failure. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:700-22. [PMID: 23860255 DOI: 10.1016/j.bbamem.2013.07.011] [Citation(s) in RCA: 116] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2013] [Revised: 07/01/2013] [Accepted: 07/08/2013] [Indexed: 12/11/2022]
Abstract
Cardiac muscle cells are equipped with specialized biochemical machineries for the rapid generation of force and movement central to the work generated by the heart. During each heart beat cardiac muscle cells perceive and experience changes in length and load, which reflect one of the fundamental principles of physiology known as the Frank-Starling law of the heart. Cardiac muscle cells are unique mechanical stretch sensors that allow the heart to increase cardiac output, and adjust it to new physiological and pathological situations. In the present review we discuss the mechano-sensory role of the cytoskeletal proteins with respect to their tight interaction with the sarcolemma and extracellular matrix. The role of contractile thick and thin filament proteins, the elastic protein titin, and their anchorage at the Z-disc and M-band, with associated proteins are reviewed in physiologic and pathologic conditions leading to heart failure. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé
Collapse
Affiliation(s)
- Vasco Sequeira
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
| | - Louise L A M Nijenkamp
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
| | - Jessica A Regan
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands; Department of Physiology, Molecular Cardiovascular Research Program, Sarver Heart Center, University of Arizona, Tucson, AZ 85724, USA
| | - Jolanda van der Velden
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands; ICIN-Netherlands Heart Institute, The Netherlands.
| |
Collapse
|
11
|
Travers T, Shao H, Wells A, Camacho C. Modeling the assembly of the multiple domains of α-actinin-4 and its role in actin cross-linking. Biophys J 2013; 104:705-15. [PMID: 23442921 PMCID: PMC3566466 DOI: 10.1016/j.bpj.2012.12.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2012] [Revised: 12/04/2012] [Accepted: 12/05/2012] [Indexed: 12/30/2022] Open
Abstract
The assembly of proteins into multidomain complexes is critical for their function. In eukaryotic nonmuscle cells, regulation of the homodimeric actin cross-linking protein α-actinin-4 (ACTN4) during cell migration involves signaling receptors with intrinsic tyrosine kinase activity, yet the underlying molecular mechanisms are poorly understood. As a first step to address the latter, we validate here an atomic model for the ACTN4 end region, which corresponds to a ternary complex between the N-terminal actin-binding domain (ABD) and an adjacent helical neck region of one monomer, and the C-terminal calmodulin-like domain of the opposite antiparallel monomer. Mutagenesis experiments designed to disrupt this ternary complex confirm that its formation reduces binding to F-actin. Molecular dynamics simulations show that the phosphomimic mutation Y265E increases actin binding by breaking several interactions that tether the two calponin homology domains into a closed ABD conformation. Simulations also show a disorder-to-order transition in the double phosphomimic mutant Y4E/Y31E of the 45-residue ACTN4 N-terminal region, which can inhibit actin binding by latching both calponin homology domains more tightly. Collectively, these studies provide a starting point for understanding the role of external cues in regulating ACTN4, with different phenotypes resulting from changes in the multidomain assembly of the protein.
Collapse
Affiliation(s)
- Timothy Travers
- Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Hanshuang Shao
- Department of Pathology, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Alan Wells
- Department of Pathology, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Carlos J. Camacho
- Department of Computational and Systems Biology, University of Pittsburgh, Pittsburgh, Pennsylvania
| |
Collapse
|
12
|
Beck MR, Otey CA, Campbell SL. Structural characterization of the interactions between palladin and α-actinin. J Mol Biol 2011; 413:712-25. [PMID: 21925511 PMCID: PMC3226707 DOI: 10.1016/j.jmb.2011.08.059] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2011] [Revised: 08/29/2011] [Accepted: 08/30/2011] [Indexed: 12/11/2022]
Abstract
The interaction between α-actinin and palladin, two actin-cross-linking proteins, is essential for proper bidirectional targeting of these proteins. As a first step toward understanding the role of this complex in organizing cytoskeletal actin, we have characterized binding interactions between the EF-hand domain of α-actinin (Act-EF34) and peptides derived from palladin and generated an NMR-derived structural model for the Act-EF34/palladin peptide complex. The critical binding site residues are similar to an α-actinin binding motif previously suggested for the complex between Act-EF34 and titin Z-repeats. The structure-based model of the Act-EF34/palladin peptide complex expands our understanding of binding specificity between the scaffold protein α-actinin and various ligands, which appears to require an α-helical motif containing four hydrophobic residues, common to many α-actinin ligands. We also provide evidence that the Family X mutation in palladin, associated with a highly penetrant form of pancreatic cancer, does not interfere with α-actinin binding.
Collapse
Affiliation(s)
- Moriah R. Beck
- Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599, USA
- Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599, USA
| | - Carol A. Otey
- Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599, USA
- Department of Cell and Molecular Physiology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599, USA
| | - Sharon L. Campbell
- Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599, USA
- Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599, USA
| |
Collapse
|
13
|
Zhang G, Chu W, Hu S, Meng T, Pan L, Zhou R, Liu Z, Zhang J. Identification and analysis of muscle-related protein isoforms expressed in the white muscle of the mandarin fish (Siniperca chuatsi). MARINE BIOTECHNOLOGY (NEW YORK, N.Y.) 2011; 13:151-162. [PMID: 20354749 DOI: 10.1007/s10126-010-9275-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2009] [Accepted: 01/19/2010] [Indexed: 05/29/2023]
Abstract
To identify muscle-related protein isoforms expressed in the white muscle of the mandarin fish Siniperca chuatsi, we analyzed 5,063 high-quality expressed sequence tags (ESTs) from white muscle cDNA library and predicted the integrity of the clusters annotated to these genes and the physiochemical properties of the putative polypeptides with full length. Up to about 33% of total ESTs were annotated to muscle-related proteins: myosin, actin, tropomyosin/troponin complex, parvalbumin, and Sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCa). Thirty-two isoforms were identified and more than one isoform existed in each of these proteins. Among these isoforms, 14 putative polypeptides were with full length. In addition, about 2% of total ESTs were significantly homologous to "glue" molecules such as alpha-actinins, myosin-binding proteins, myomesin, tropomodulin, cofilin, profilin, twinfilins, coronin-1, and nebulin, which were required for the integrity and maintenance of the muscle sarcomere. The results demonstrated that multiple isoforms of major muscle-related proteins were expressed in S. chuatsi white muscle. The analysis on these isoforms and other proteins sequences will greatly aid our systematic understanding of the high flexibility of mandarin fish white muscle at molecular level and expand the utility of fish systems as models for the muscle genetic control and function.
Collapse
Affiliation(s)
- Guoqiang Zhang
- Key Laboratory of Genome Information and Sciences, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing, 100029, People's Republic of China
| | | | | | | | | | | | | | | |
Collapse
|
14
|
Berman Y, North KN. A gene for speed: the emerging role of alpha-actinin-3 in muscle metabolism. Physiology (Bethesda) 2010; 25:250-9. [PMID: 20699471 DOI: 10.1152/physiol.00008.2010] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A common polymorphism (R577X) in the ACTN3 gene results in complete deficiency of alpha-actinin-3 protein in approximately 16% of humans worldwide. The presence of alpha-actinin-3 protein is associated with improved sprint/power performance in athletes and the general population. Despite this, there is evidence that the null genotype XX has been acted on by recent positive selection, likely due to its emerging role in the regulation of muscle metabolism. alpha-Actinin-3 deficiency reduces the activity of glycogen phosphorylase and results in a fundamental shift toward more oxidative pathways of energy utilization.
Collapse
Affiliation(s)
- Yemima Berman
- Institute for Neuroscience and Muscle Research, The Children's Hospital at Westmead, Westmead, Australia
| | | |
Collapse
|
15
|
Ali MAM, Cho WJ, Hudson B, Kassiri Z, Granzier H, Schulz R. Titin is a target of matrix metalloproteinase-2: implications in myocardial ischemia/reperfusion injury. Circulation 2010; 122:2039-47. [PMID: 21041693 DOI: 10.1161/circulationaha.109.930222] [Citation(s) in RCA: 144] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
BACKGROUND Titin is the largest mammalian (≈3000 to 4000 kDa) and myofilament protein that acts as a molecular spring in the cardiac sarcomere and determines systolic and diastolic function. Loss of titin in ischemic hearts has been reported, but the mechanism of titin degradation is not well understood. Matrix metalloproteinase-2 (MMP-2) is localized to the cardiac sarcomere and, on activation in ischemia/reperfusion injury, proteolyzes specific myofilament proteins. Here we determine whether titin is an intracellular substrate for MMP-2 and if its degradation during ischemia/reperfusion contributes to cardiac contractile dysfunction. METHODS AND RESULTS Immunohistochemistry and confocal microscopy in rat and human hearts showed discrete colocalization between MMP-2 and titin in the Z-disk region of titin and that MMP-2 is localized mainly to titin near the Z disk of the cardiac sarcomere. Both purified titin and titin in skinned cardiomyocytes were proteolyzed when incubated with MMP-2 in a concentration-dependent manner, and this was prevented by MMP inhibitors. Isolated rat hearts subjected to ischemia/reperfusion injury showed cleavage of titin in ventricular extracts by gel electrophoresis, which was confirmed by reduced titin immunostaining in tissue sections. Inhibition of MMP activity with ONO-4817 prevented ischemia/reperfusion-induced titin degradation and improved the recovery of myocardial contractile function. Titin degradation was also reduced in hearts from MMP-2 knockout mice subjected to ischemia/reperfusion in vivo compared with wild-type controls. CONCLUSION MMP-2 localizes to titin at the Z-disk region of the cardiac sarcomere and contributes to titin degradation in myocardial ischemia/reperfusion injury.
Collapse
Affiliation(s)
- Mohammad A M Ali
- Department of Pharmacology, Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada
| | | | | | | | | | | |
Collapse
|
16
|
Natural and semisynthetic azaphilones as a new scaffold for Hsp90 inhibitors. Bioorg Med Chem 2010; 18:6031-43. [PMID: 20655237 DOI: 10.1016/j.bmc.2010.06.068] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2010] [Revised: 06/16/2010] [Accepted: 06/20/2010] [Indexed: 11/21/2022]
Abstract
A series of mold metabolites of Ascomycetes, structurally belonging to the class of azaphilones, were found to inhibit the heat shock protein Hsp90. In particular, bulgarialactone B was tested for its binding to Hsp90 using surface plasmon resonance and limited proteolysis assays and for its effects on Hsp90 client proteins expression in a series of human tumor cell lines. This compound showed high affinity for Hsp90, interacting with the 90-280 region of the N-terminal domain and down-regulated the Hsp90 client proteins Raf-1, survivin, Cdk4, Akt, and EGFR. Bulgarialactone B and other natural azaphilones showed antiproliferative activity in a panel of human tumor cell lines; their conversion into semisynthetic derivatives by reaction with primary amines increased the antiproliferative activity. Preliminary results indicated in vivo activity of bulgarialactone B against an ascitic ovarian carcinoma xenograft, thus supporting the therapeutic potential of this novel series of Hsp90 inhibitors.
Collapse
|
17
|
Dynamic strength of titin's Z-disk end. J Biomed Biotechnol 2010; 2010:838530. [PMID: 20414364 PMCID: PMC2857871 DOI: 10.1155/2010/838530] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2009] [Accepted: 02/11/2010] [Indexed: 11/17/2022] Open
Abstract
Titin is a giant filamentous protein traversing the half sarcomere of striated muscle with putative functions as diverse as providing structural template, generating elastic response, and sensing and relaying mechanical information. The Z-disk region of titin, which corresponds to the N-terminal end of the molecule, has been thought to be a hot spot for mechanosensing while also serving as anchorage for its sarcomeric attachment. Understanding the mechanics of titin's Z-disk region, particularly under the effect of binding proteins, is of great interest. Here we briefly review recent findings on the structure, molecular associations, and mechanics of titin's Z-disk region. In addition, we report experimental results on the dynamic strength of titin's Z1Z2 domains measured by nanomechanical manipulation of the chemical dimer of a recombinant protein fragment.
Collapse
|
18
|
Giommarelli C, Zuco V, Favini E, Pisano C, Dal Piaz F, De Tommasi N, Zunino F. The enhancement of antiproliferative and proapoptotic activity of HDAC inhibitors by curcumin is mediated by Hsp90 inhibition. Cell Mol Life Sci 2010; 67:995-1004. [PMID: 20039095 PMCID: PMC11115870 DOI: 10.1007/s00018-009-0233-x] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2009] [Revised: 11/09/2009] [Accepted: 12/09/2009] [Indexed: 12/17/2022]
Abstract
Curcumin, a natural polyphenol, has been described to exhibit effects on signaling pathways, leading to induction of apoptosis. In this study, we observed that curcumin inhibited Hsp90 activity causing depletion of client proteins implicated in survival pathways. Based on this observation, this study was designed to investigate the cellular effects of curcumin combination with the pan-HDAC inhibitors, vorinostat and panobinostat, which induce hyperacetylation of Hsp90, resulting in inhibition of its chaperone function. The results showed that, at subtoxic concentrations, curcumin markedly sensitized tumor cells to vorinostat- and panobinostat-induced growth inhibition and apoptosis. The sensitization was associated with persistent depletion of Hsp90 client proteins (EGFR, Raf-1, Akt, and survivin). In conclusion, our findings document a novel mechanism of action of curcumin and support the therapeutic potential of curcumin/HDAC inhibitors combination, because the synergistic interaction was observed at pharmacologically achievable concentrations, which were ineffective when each drug was used alone.
Collapse
Affiliation(s)
- Chiara Giommarelli
- Fondazione IRCCS Istituto Nazionale Tumori, Via Venezian 1, 20133 Milan, Italy
| | - Valentina Zuco
- Fondazione IRCCS Istituto Nazionale Tumori, Via Venezian 1, 20133 Milan, Italy
| | - Enrica Favini
- Fondazione IRCCS Istituto Nazionale Tumori, Via Venezian 1, 20133 Milan, Italy
| | | | - Fabrizio Dal Piaz
- Dipartimento di Scienze Farmaceutiche, Università di Salerno, 84100 Salerno, Italy
| | | | - Franco Zunino
- Fondazione IRCCS Istituto Nazionale Tumori, Via Venezian 1, 20133 Milan, Italy
| |
Collapse
|
19
|
Luther PK. The vertebrate muscle Z-disc: sarcomere anchor for structure and signalling. J Muscle Res Cell Motil 2009; 30:171-85. [PMID: 19830582 PMCID: PMC2799012 DOI: 10.1007/s10974-009-9189-6] [Citation(s) in RCA: 158] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2009] [Accepted: 09/23/2009] [Indexed: 02/04/2023]
Abstract
The Z-disc, appearing as a fine dense line forming sarcomere boundaries in striated muscles, when studied in detail reveals crosslinked filament arrays that transmit tension and house myriads of proteins with diverse functions. At the Z-disc the barbed ends of the antiparallel actin filaments from adjoining sarcomeres interdigitate and are crosslinked primarily by layers of α-actinin. The Z-disc is therefore the site of polarity reversal of the actin filaments, as needed to interact with the bipolar myosin filaments in successive sarcomeres. The layers of α-actinin determine the Z-disc width: fast fibres have narrow (~30–50 nm) Z-discs and slow and cardiac fibres have wide (~100 nm) Z-discs. Comprehensive reviews on the roles of the numerous proteins located at the Z-disc in signalling and disease have been published; the aim here is different, namely to review the advances in structural aspects of the Z-disc.
Collapse
Affiliation(s)
- Pradeep K Luther
- Molecular Medicine Section, National Heart and Lung Institute, Imperial College London, London, UK.
| |
Collapse
|
20
|
Kontrogianni-Konstantopoulos A, Ackermann MA, Bowman AL, Yap SV, Bloch RJ. Muscle giants: molecular scaffolds in sarcomerogenesis. Physiol Rev 2009; 89:1217-67. [PMID: 19789381 PMCID: PMC3076733 DOI: 10.1152/physrev.00017.2009] [Citation(s) in RCA: 184] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Myofibrillogenesis in striated muscles is a highly complex process that depends on the coordinated assembly and integration of a large number of contractile, cytoskeletal, and signaling proteins into regular arrays, the sarcomeres. It is also associated with the stereotypical assembly of the sarcoplasmic reticulum and the transverse tubules around each sarcomere. Three giant, muscle-specific proteins, titin (3-4 MDa), nebulin (600-800 kDa), and obscurin (approximately 720-900 kDa), have been proposed to play important roles in the assembly and stabilization of sarcomeres. There is a large amount of data showing that each of these molecules interacts with several to many different protein ligands, regulating their activity and localizing them to particular sites within or surrounding sarcomeres. Consistent with this, mutations in each of these proteins have been linked to skeletal and cardiac myopathies or to muscular dystrophies. The evidence that any of them plays a role as a "molecular template," "molecular blueprint," or "molecular ruler" is less definitive, however. Here we review the structure and function of titin, nebulin, and obscurin, with the literature supporting a role for them as scaffolding molecules and the contradictory evidence regarding their roles as molecular guides in sarcomerogenesis.
Collapse
|
21
|
Qi J, Chi L, Labeit S, Banes AJ. Nuclear localization of the titin Z1Z2Zr domain and role in regulating cell proliferation. Am J Physiol Cell Physiol 2008; 295:C975-85. [PMID: 18684985 DOI: 10.1152/ajpcell.90619.2007] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Titin (also called connectin) is a major protein in sarcomere assembly as well as providing elastic return of the sarcomere postcontraction in cardiac and striated skeletal muscle tissues. In addition, it has been speculated that titin is associated with nuclear functions, including chromosome and spindle formation, and regulation of muscle gene expression. In the present study, a short isoform of titin was detected in a human osteoblastic cell line, MG-63 cells, by both immunostaining and Western blot analysis. Confocal images of titin staining showed both cytoplasmic and nuclear localization in a punctate pattern. Therefore, we hypothesized that human titin may contain a nuclear localization signal (NLS). A functional NLS, 200-PAKKTKT-206, located in a low-complexity, titin-specific region between Z2 and Z repeats, was found by sequentially deleting segments of the NH(2)-terminal sequence in conjunction with an enhanced green fluorescent protein reporter system and confirmed by site-directed mutagenesis. Overexpression of titin's amino terminal fragment (Z1Z2Zr) in human osteoblasts (MG-63) increased cell proliferation by activating the Wnt/beta-catenin pathway. RT-PCR screens of tissue panels demonstrated that residues 1-206 were ubiquitously expressed at low levels in all tissues and cell types analyzed. Our data implicate a dual role for titin's amino terminal region, i.e., a novel nuclear function promoting cell division in addition to its known structural role in Z-line assembly.
Collapse
Affiliation(s)
- Jie Qi
- Flexcell International Corporation, Hillsborough, North Carolina 27278, USA
| | | | | | | |
Collapse
|
22
|
Chi RJ, Simon AR, Bienkiewicz EA, Felix A, Keller TCS. Smooth muscle titin Zq domain interaction with the smooth muscle alpha-actinin central rod. J Biol Chem 2008; 283:20959-67. [PMID: 18519573 DOI: 10.1074/jbc.m709621200] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Actin-myosin II filament-based contractile structures in striated muscle, smooth muscle, and nonmuscle cells contain the actin filament-cross-linking protein alpha-actinin. In striated muscle Z-disks, alpha-actinin interacts with N-terminal domains of titin to provide a structural linkage crucial for the integrity of the sarcomere. We previously discovered a long titin isoform, originally smitin, hereafter sm-titin, in smooth muscle and demonstrated that native sm-titin interacts with C-terminal EF hand region and central rod R2-R3 spectrin-like repeat region sites in alpha-actinin. Reverse transcription-PCR analysis of RNA from human adult smooth muscles and cultured rat smooth muscle cells and Western blot analysis with a domain-specific antibody presented here revealed that sm-titin contains the titin gene-encoded Zq domain that may bind to the alpha-actinin R2-R3 central rod domain as well as Z-repeat domains that bind to the EF hand region. We investigated whether the sm-titin Zq domain binds to alpha-actinin R2 and R3 spectrin repeat-like domain loops that lie in proximity with two-fold symmetry on the surface of the central rod. Mutations in alpha-actinin R2 and R3 domain loop residues decreased interaction with expressed sm-titin Zq domain in glutathione S-transferase pull-down and solid phase binding assays. Alanine mutation of a region of the Zq domain with high propensity for alpha-helix formation decreased apparent Zq domain dimer formation and decreased Zq interaction with the alpha-actinin R2-R3 region in surface plasmon resonance assays. We present a model in which two sm-titin Zq domains interact with each other and with the two R2-R3 sites in the alpha-actinin central rod.
Collapse
Affiliation(s)
- Richard J Chi
- Department of Biological Science, College of Medicine, Florida State University, Tallahassee, FL 32306, USA
| | | | | | | | | |
Collapse
|
23
|
Dyachenko V, Christ A, Gubanov R, Isenberg G. Bending of z-lines by mechanical stimuli: an input signal for integrin dependent modulation of ion channels? PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2008; 97:196-216. [PMID: 18367237 DOI: 10.1016/j.pbiomolbio.2008.02.007] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
We studied which components of mechanical cell deformation are involved in "stretch modulated ion currents" (SMIC). Murine ventricular myocytes were attached to glass coverslips and deformed in x, y and z with a 16 microm thin glass stylus (S) of calibrated stiffness. Three-dimensional confocal microscopy characterized cell deformation (T-tubular membranes, mitochondria) and bending of S (indicative of the applied force). Axial (x-) displacement of S sheared the upper cell part versus the attached bottom, close to S, it changed sarcomere length and bent z-lines ("z-line displacement"). Vertical (z-press) or transversal (y-shear) displacement of S bulged cytoplasm and mitochondria transversally without detectable z-line displacement. Axial stiffness increased with the extent of stress ("stress stiffening"). Depolymerization of F-actin or block of integrin receptors reduced stiffness. SMIC served as a proxy readout of deformation-induced signaling. Axial deformation activated a non-selective cation conductance (Gns) and deactivated an inwardly rectifying K+ conductance (GK1), z-press or y-shear did not induce SMIC. Depolymerization of F-actin or block of integrin receptors reduced SMIC. SMIC did not depend on changes in sarcomere length but correlated with the extent of z-line bending. We discuss that both shear stress at the attached cell bottom and z-line bending could activate mechanosensors. Since SMIC was absent during deformations without z-line bending we postulate that z-line bending is a necessary component for SMIC signaling.
Collapse
Affiliation(s)
- V Dyachenko
- Department of Physiology, Martin-Luther-University Halle, Halle, Germany
| | | | | | | |
Collapse
|
24
|
Getun IV, Brown CK, Tulla-Puche J, Ohlendorf D, Woodward C, Barany G. Partially Folded Bovine Pancreatic Trypsin Inhibitor Analogues Attain Fully Native Structures when Co-Crystallized with S195A Rat Trypsin. J Mol Biol 2008; 375:812-23. [DOI: 10.1016/j.jmb.2007.10.084] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2007] [Revised: 10/28/2007] [Accepted: 10/30/2007] [Indexed: 11/24/2022]
|
25
|
Cavnar PJ, Olenych SG, Keller TCS. Molecular identification and localization of cellular titin, a novel titin isoform in the fibroblast stress fiber. ACTA ACUST UNITED AC 2007; 64:418-33. [PMID: 17366640 DOI: 10.1002/cm.20193] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
We previously discovered a large titin-like protein-c-titin-in chicken epithelial brush border and human blood platelet extracts that binds alpha-actinin and organizes arrays of myosin II bipolar filaments in vitro. RT-PCR analysis of total RNA from human megakaryoblastic (CHRF-288-11) and mouse fibroblast (3T3) nonmuscle cells reveal sequences identical to known titin gene exon sequences that encode parts of the Z-line, I-band, PEVK domain, A-band, and M-line regions of striated muscle titins. In the nonmuscle cells, these sequences are differentially spliced in patterns not reported for any striated muscle titin isoform. Rabbit polyclonal antibodies raised against expressed protein fragments encoded by the Z-repeat and kinase domain regions react with the c-titin band in Western blot analysis of platelet extracts and immunoprecipitate c-titin in whole platelet extracts. Immunofluorescent localization demonstrates that the majority of the c-titin colocalizes with alpha-actinin and actin in 3T3 and Indian Muntjac deer skin fibroblast stress fibers. Our results suggest that differential expression of titin gene exons in nonmuscle cells yields multiple novel isoforms of the protein c-titin that are associated with the actin stress fiber structures.
Collapse
Affiliation(s)
- Peter J Cavnar
- Department of Biological Science, Florida State University, Tallahassee, FL 32306-4370, USA
| | | | | |
Collapse
|
26
|
Chi RJ, Olenych SG, Kim K, Keller TCS. Smooth muscle alpha-actinin interaction with smitin. Int J Biochem Cell Biol 2005; 37:1470-82. [PMID: 15833278 DOI: 10.1016/j.biocel.2005.02.014] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2004] [Accepted: 02/14/2005] [Indexed: 11/19/2022]
Abstract
Actin-myosin II filament-based contractile structures in striated muscle, smooth muscle, and nonmuscle cells also contain the actin filament-crosslinking protein alpha-actinin. In striated muscle sarcomeres, interactions between the myosin-binding protein titin and alpha-actinin in the Z-line provide an important structural linkage. We previously discovered a titin-like protein, smitin, associated with the contractile apparatus of smooth muscle cells. Purified native smooth muscle alpha-actinin binds with nanomolar affinity to smitin in smitin-myosin coassemblies in vitro. Smooth muscle alpha-actinin also interacts with striated muscle titin. In contrast to striated muscle alpha-actinin interaction with titin and smitin, which is significantly enhanced by PIP2, smooth muscle alpha-actinin interacts with smitin and titin equally well in the presence and absence of PIP2. Using expressed regions of smooth muscle alpha-actinin, we have demonstrated smitin-binding sites in the smooth muscle alpha-actinin R2-R3 spectrin-like repeat rod domain and a C-terminal domain formed by cryptic EF-hand structures. These smitin-binding sites are highly homologous to the titin-binding sites of striated muscle alpha-actinin. Our results suggest that direct interaction between alpha-actinin and titin or titin-like proteins is a common feature of actin-myosin II contractile structures in striated muscle and smooth muscle cells and that the molecular bases for alpha-actinin interaction with these proteins are similar, although regulation of these interactions may differ according to tissue.
Collapse
Affiliation(s)
- Richard J Chi
- Department of Biological Science, Florida State University, Tallahassee, FL 32306-4370, USA
| | | | | | | |
Collapse
|
27
|
Squire JM, Al-Khayat HA, Knupp C, Luther PK. Molecular Architecture in Muscle Contractile Assemblies. ADVANCES IN PROTEIN CHEMISTRY 2005; 71:17-87. [PMID: 16230109 DOI: 10.1016/s0065-3233(04)71002-5] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- John M Squire
- Biological Structure and Function Section, Biomedical Sciences Division, Imperial College London, London SW7 2AZ, United Kindom
| | | | | | | |
Collapse
|
28
|
Casbarra A, Birolo L, Infusini G, Dal Piaz F, Svensson M, Pucci P, Svanborg C, Marino G. Conformational analysis of HAMLET, the folding variant of human alpha-lactalbumin associated with apoptosis. Protein Sci 2004; 13:1322-30. [PMID: 15075403 PMCID: PMC2286754 DOI: 10.1110/ps.03474704] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2003] [Revised: 01/12/2004] [Accepted: 01/15/2004] [Indexed: 10/26/2022]
Abstract
A combination of hydrogen/deuterium (H/D) exchange and limited proteolysis experiments coupled to mass spectrometry analysis was used to depict the conformation in solution of HAMLET, the folding variant of human alpha-lactalbumin, complexed to oleic acid, that induces apoptosis in tumor and immature cells. Although near- and far-UV CD and fluorescence spectroscopy were not able to discriminate between HAMLET and apo-alpha-lactalbumin, H/D exchange experiments clearly showed that they correspond to two distinct conformational states, with HAMLET incorporating a greater number of deuterium atoms than the apo and holo forms. Complementary proteolysis experiments revealed that HAMLET and apo are both accessible to proteases in the beta-domain but showed substantial differences in accessibility to proteases at specific sites. The overall results indicated that the conformational changes associated with the release of Ca2+ are not sufficient to induce the HAMLET conformation. Metal depletion might represent the first event to produce a partial unfolding in the beta-domain of alpha-lactalbumin, but some more unfolding is needed to generate the active conformation HAMLET, very likely allowing the protein to bind the C18:1 fatty acid moiety. On the basis of these data, a putative binding site of the oleic acid, which stabilizes the HAMLET conformation, is proposed.
Collapse
Affiliation(s)
- Annarita Casbarra
- Dipartimento di Chimica Organica e Biochimica, Università di Napoli Federico II, I-80126 Napoli, Italy
| | | | | | | | | | | | | | | |
Collapse
|
29
|
Luther PK, Padrón R, Ritter S, Craig R, Squire JM. Heterogeneity of Z-band structure within a single muscle sarcomere: implications for sarcomere assembly. J Mol Biol 2003; 332:161-9. [PMID: 12946354 DOI: 10.1016/s0022-2836(03)00883-0] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The vertebrate striated muscle Z-band connects actin filaments of opposite polarity from adjacent sarcomeres and allows tension to be transmitted along a myofibril during contraction. Z-bands in different muscles have a modular structure formed by layers of alpha-actinin molecules cross-linking actin filaments. Successive layers occur at 19 nm intervals and have 90 degrees rotations between them. 3D reconstruction from electron micrographs show a two-layer "simple" Z-band in fish body fast muscle, a three-layer Z-band in fish fin fast muscle, and a six-layer Z-band in mammalian slow muscle. Related to the number of these layers, longitudinal sections of the Z-band show a number of zigzag connections between the oppositely oriented actin filaments. The number of layers also determines the axial width of the Z-band, which is a useful indicator of fibre type; fast fibres have narrow (approximately 30-50 nm) Z-bands; slow and cardiac fibres have wide (approximately 100-140 nm) Z-bands. Here, we report the first observation of two different Z-band widths within a single sarcomere. By comparison with previous studies, the narrower Z-band comprises three layers. Since the increase in width of the wider Z-band is about 19 nm, we conclude that it comprises four layers. This finding is consistent with a Z-band assembly model involving molecular control mechanisms that can add additional layers of 19 nm periodicity. These multiple Z-band structures suggest that different isoforms of nebulin and titin with a variable number of Z-repeats could be present within a single sarcomere.
Collapse
Affiliation(s)
- Pradeep K Luther
- Biological Structure and Function Section, Division of Biomedical Sciences, Faculty of Medicine, Imperial College London, Exhibition Road, London SW7 2AZ, UK.
| | | | | | | | | |
Collapse
|
30
|
Abstract
The human essential splicing factor U2AF (U2 auxiliary factor) consists of 35 and 65 kDa subunits which form a highly stable heterodimer in solution. Copurification of the recombinant U2AF35 RNA recognition motif (U2AF35 RRM) and full-length U2AF65 yields a soluble and functionally active minimal U2AF heterodimer. Recombinant U2AF35 RRM protein free and in complex with three different regions of U2AF65 was characterized by nuclear magnetic resonance spectroscopy. We found that the recombinant U2AF35 RRM is unstructured in solution but its tertiary structure is induced upon binding to U2AF65. This interaction is mediated by the N-terminal proline-rich region of U2AF65 and does not involve the U2AF65 RRMs.
Collapse
Affiliation(s)
- Esther Kellenberger
- Structural and Computational Biology Programme, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany.
| | | | | |
Collapse
|
31
|
Monti M, Principe S, Giorgetti S, Mangione P, Merlini G, Clark A, Bellotti V, Amoresano A, Pucci P. Topological investigation of amyloid fibrils obtained from beta2-microglobulin. Protein Sci 2002; 11:2362-9. [PMID: 12237458 PMCID: PMC2373708 DOI: 10.1110/ps.0206902] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Amyloid fibrils of patients treated with regular hemodialysis essentially consists of beta2-microglobulin (beta2-m) and its truncated species DeltaN6beta2-m lacking six residues at the amino terminus. The truncated fragment has a more flexible three-dimensional structure and constitutes an excellent candidate for the analysis of a protein in the amyloidogenic conformation. The surface topology of synthetic fibrils obtained from intact beta2-m and truncated DeltaN6beta2-m was investigated by the limited proteolysis/mass spectrometry approach that appeared particularly suited to gain insights into the structure of beta2-m within the fibrillar polymer. The distribution of prefential proteolytic sites observed in both fibrils revealed that the central region of the protein, which had been easily cleaved in the full-length globular beta2-m, was fully protected in the fibrillar form. In addition, the amino- and carboxy-terminal regions of beta2-m became exposed to the solvent in the fibrils, whereas they were masked completely in the native protein. These data indicate that beta2-m molecules in the fibrils consist of an unaccessible core comprising residues 20-87 with the strands I and VIII being not constrained in the fibrillar polymer and exposed to the proteases. Moreover, proteolytic cleavages observed in vitro at Lys 6 and Lys 19 reproduce specific cleavages that have to occur in vivo to generate the truncated forms of beta2-m occurring in natural fibrils. On the basis of these data, a possible mechanism for fibril formation from native beta2-m is discussed and an explanation for the occurrence of truncated protein species in natural fibrils is given.
Collapse
Affiliation(s)
- Maria Monti
- Dipartimento di Chimica Organica e Biochimica, Università di Napoli Federico II, via Cinthia 6, Italy
| | | | | | | | | | | | | | | | | |
Collapse
|
32
|
Casbarra A, Piaz FD, Ingallinella P, Orrù S, Pucci P, Pessi A, Bianchi E. The effect of prime-site occupancy on the hepatitis C virus NS3 protease structure. Protein Sci 2002; 11:2102-12. [PMID: 12192066 PMCID: PMC2373603 DOI: 10.1110/ps.0206602] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
We recently reported a new class of inhibitors of the chymotrypsin-like serine protease NS3 of the hepatitis C virus. These inhibitors exploit the binding potential of the S' site of the protease, which is not generally used by the natural substrates. The effect of prime-site occupancy was analyzed by circular dichroism spectroscopy and limited proteolysis-mass spectrometry. Generally, nonprime inhibitors cause a structural change in NS3. Binding in the S' site produces additional conformational changes with different binding modes, even in the case of the NS3/4A cofactor complex. Notably, inhibitor binding either in the S or S' site also has profound effects on the stabilization of the protease. In addition, the stabilization propagates to regions not in direct contact with the inhibitor. In particular, the N-terminal region, which according to structural studies is endowed with low structural stability and is not stabilized by nonprime inhibitors, was now fully protected from proteolytic degradation. From the perspective of drug design, P-P' inhibitors take advantage of binding pockets, which are not exploited by the natural HCV substrates; hence, they are an entry point for a novel class of NS3/4A inhibitors. Here we show that binding of each inhibitor is associated with a specific structural rearrangement. The development of a range of inhibitors belonging to different classes and an understanding of their interactions with the protease are required to address the issue of the most likely outcome of viral protease inhibitor therapy, that is, viral resistance.
Collapse
Affiliation(s)
- Annarita Casbarra
- Dipartimento di Chimica Organica e Biochimica, Complesso Universitario Monte Santangelo, Via Cinthia, 80126 Napoli, Italy
| | | | | | | | | | | | | |
Collapse
|
33
|
Luther PK, Squire JM. Muscle Z-band ultrastructure: titin Z-repeats and Z-band periodicities do not match. J Mol Biol 2002; 319:1157-64. [PMID: 12079354 DOI: 10.1016/s0022-2836(02)00372-8] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Vertebrate muscle Z-bands show zig-zag densities due to different sets of alpha-actinin cross-links between anti-parallel actin molecules. Their axial extent varies with muscle and fibre type: approximately 50 nm in fast and approximately 100 nm in cardiac and slow muscles, corresponding to the number of alpha-actinin cross-links present. Fish white (fast) muscle Z-bands have two sets of alpha-actinin links, mammalian slow muscle Z-bands have six. The modular structure of the approximately 3 MDa protein titin that spans from M-band to Z-band correlates with the axial structure of the sarcomere; it may form the template for myofibril assembly. The Z-band-located amino-terminal 80 kDa of titin includes 45 residue repeating modules (Z-repeats) that are expressed differentially; heart, slow and fast muscles have seven, four to six and two to four Z-repeats, respectively. Gautel et al. proposed a Z-band model in which each Z-repeat links to one level of alpha-actinin cross-links, requiring that the axial extent of a Z-repeat is the same as the axial separation of alpha-actinin layers, of which there are two in every actin crossover repeat. The span of a Z-repeat in vitro is estimated by Atkinson et al. to be 12 nm or less; much less than half the normal vertebrate muscle actin crossover length of 36 nm. Different actin-binding proteins can change this length; it is reduced markedly by cofilin binding, or can increase to 38.5 nm in the abnormally large nemaline myopathy Z-band. Here, we tested whether in normal vertebrate Z-bands there is a marked reduction in crossover repeat so that it matches twice the apparent Z-repeat length of 12 nm. We found that the measured periodicities in wide Z-bands in slow and cardiac muscles are all very similar, about 39 nm, just like the nemaline myopathy Z-bands. Hence, the 39 nm periodicity is an important conserved feature of Z-bands and either cannot be explained by titin Z-repeats as previously suggested or may correlate with two Z-repeats.
Collapse
Affiliation(s)
- Pradeep K Luther
- Biological Structure and Function Section, Biomedical Sciences Division, Faculty of Medicine, Imperial College, Exhibition Road, London SW7 2AZ, UK.
| | | |
Collapse
|
34
|
Birolo L, Dal Piaz F, Pucci P, Marino G. Structural characterization of the M* partly folded intermediate of wild type and P138A aspartate aminotransferase from Escherichia coli. J Biol Chem 2002; 277:17428-37. [PMID: 11875074 DOI: 10.1074/jbc.m200650200] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A combination of spectroscopic techniques, hydrogen/deuterium exchange, and limited proteolysis experiments coupled to mass spectrometry analysis was used to depict the topology of the monomeric M* partly folded intermediate of aspartate aminotransferase from Escherichia coli in wild type (WT) as well as in a mutant form in which the highly conserved cis-proline at position 138 was replaced by a trans-alanine (P138A). Fluorescence analysis indicates that, although M* is an off-pathway intermediate in the folding of WT aspartate aminotransferase from E. coli, it seems to coincide with an on-pathway folding intermediate for the P138A mutant. Spectroscopic data, hydrogen/deuterium exchange, and limited proteolysis experiments demonstrated the occurrence of conformational differences between the two M* intermediates, with P138A-M* being conceivably more compact than WT-M*. Limited proteolysis data suggested that these conformational differences might be related to a different relative orientation of the small and large domains of the protein induced by the presence of the cis-proline residue at position 138. These differences between the two M* species indicated that in WT-M* Pro138 is in the cis conformation at this stage of the folding process. Moreover, hydrogen/deuterium exchange results showed the occurrence of few differences in the native N(2) forms of WT and P138A, the spectroscopic features and crystallographic structures of which are almost superimposable.
Collapse
Affiliation(s)
- Leila Birolo
- Dipartimento di Chimica Organica e Biochimica, Università Federico II di Napoli, Complesso Universitario Monte Sant'Angelo, Via Cinthia, 80126 Napoli, Italy.
| | | | | | | |
Collapse
|
35
|
Luther PK, Barry JS, Squire JM. The three-dimensional structure of a vertebrate wide (slow muscle) Z-band: lessons on Z-band assembly. J Mol Biol 2002; 315:9-20. [PMID: 11771963 DOI: 10.1006/jmbi.2001.5217] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The vertebrate muscle Z-band organizes and tethers antiparallel actin filaments in adjacent sarcomeres and hence propagates the tension generated by the actomyosin interaction during muscular contraction. The axial width of the Z-band varies with fibre and muscle type: fast twitch muscles have narrow (approximately 30-50 nm) Z-bands, while slow-twitch and cardiac muscles have wide (approximately 100-140 nm) Z-bands. In electron micrographs of longitudinal sections of fast fibres like those found in fish body white muscle, the Z-band appears as a characteristic zigzag layer of density connecting the mutually offset actin filament arrays in adjacent sarcomeres. Wide Z-bands in slow fibres such as the one studied here (bovine neck muscle) show a stack of three or four zigzag layers. The variable Z-band width incorporating variable numbers of zigzag layers presumably relates to the different mechanical properties of the respective muscles. Three-dimensional reconstructions of Z-bands reveal that individual zigzag layers are often composed of more than one set of protein bridges, called Z-links, probably alpha-actinin, between oppositely oriented actin filaments. Fast muscle Z-bands comprise two or three layers of Z-links. Here we have applied Fourier reconstruction methods to obtain clear three-dimensional density maps of the Z-bands in beef muscle. The bovine slow muscle investigated here reveals a Z-band comprising six sets of Z-links, which, due to their shape and the way their projected densities overlap, appear in longitudinal sections as either three or four zigzag layers, depending on the lattice view. There has been great interest recently in the suggestion that Z-band variability with fibre type may be due to differences in the repetitive region (tandem Z-repeats) in the Z-band part of titin (also called connectin). We discuss this in the context of our results and present a systematic classification of Z-band types according to the numbers of Z-links and titin Z-repeats.
Collapse
Affiliation(s)
- Pradeep K Luther
- Biological Structure and Function Section, Biomedical Sciences Division, Faculty of Medicine, Imperial College, Exhibition Road, London, SW7 2AZ, UK.
| | | | | |
Collapse
|
36
|
Young P, Gautel M. The interaction of titin and alpha-actinin is controlled by a phospholipid-regulated intramolecular pseudoligand mechanism. EMBO J 2000; 19:6331-40. [PMID: 11101506 PMCID: PMC305858 DOI: 10.1093/emboj/19.23.6331] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The assembly of stable cytoskeletal structures from dynamically recycled molecules requires developmental and spatial regulation of protein interactions. In muscle, titin acts as a molecular ruler organizing the actin cytoskeleton via interactions with many sarcomeric proteins, including the crosslinking protein alpha-actinin. An interaction between the C-terminal domain of alpha-actinin and titin Z-repeat motifs targets alpha-actinin to the Z-disk. Here we investigate the cellular regulation of this interaction. alpha-actinin is a rod shaped head-to-tail homodimer. In contrast to C-terminal fragments, full-length alpha-actinin does not bind Z-repeats. We identify a 30-residue Z-repeat homologous sequence between the actin-binding and rod regions of alpha-actinin that binds the C-terminal domain with nanomolar affinity. Thus, Z-repeat binding is prevented by this 'pseudoligand' interaction between the subunits of the alpha-actinin dimer. This autoinhibition is relieved upon binding of the Z-disk lipid phosphatidylinositol-bisphosphate to the actin-binding domain. We suggest that this novel mechanism is relevant to control the site-specific interactions of alpha-actinin during sarcomere assembly and turnover. The intramolecular contacts defined here also constrain a structural model for intrasterical regulation of all alpha-actinin isoforms.
Collapse
Affiliation(s)
- P Young
- European Molecular Biology Laboratory, Structural Biology Division, 69012 Heidelberg, Germany
| | | |
Collapse
|