1
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Hao J, Liu C, Zhang N, Li J, Ni T, Qu M, Li XD. Alternative relay regulates the adenosine triphosphatase activity of Locusta migratoria striated muscle myosin. INSECT SCIENCE 2024; 31:435-447. [PMID: 37489033 DOI: 10.1111/1744-7917.13257] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2022] [Revised: 06/20/2023] [Accepted: 06/24/2023] [Indexed: 07/26/2023]
Abstract
Locust (Locusta migratoria) has a single striated muscle myosin heavy chain (Mhc) gene, which contains 5 clusters of alternative exclusive exons and 1 differently included penultimate exon. The alternative exons of Mhc gene encode 4 distinct regions in the myosin motor domain, that is, the N-terminal SH3-like domain, one lip of the nucleotide-binding pocket, the relay, and the converter. Here, we investigated the role of the alternative regions on the motor function of locust muscle myosin. Using Sf9-baculovirus protein expression system, we expressed and purified 5 isoforms of the locust muscle myosin heavy meromyosin (HMM), including the major isoform in the thorax dorsal longitudinal flight muscle (FL1) and 4 isoforms expressed in the abdominal intersegmental muscle (AB1 to AB4). Among these 5 HMMs, FL1-HMM displayed the highest level of actin-activated adenosine triphosphatase (ATPase) activity (hereafter referred as ATPase activity). To identify the alternative region(s) responsible for the elevated ATPase activity of FL1-HMM, we produced a number of chimeras of FL1-HMM and AB4-HMM. Substitution with the relay of AB4-HMM (encoded by exon-14c) substantially decreased the ATPase activity of FL1-HMM, and conversely, the relay of FL1-HMM (encoded by exon-14a) enhanced the ATPase activity of AB4-HMM. Mutagenesis showed that the exon-14a-encoded residues Gly474 and Asn509 are responsible for the elevated ATPase activity of FL1-HMM. Those results indicate that the alternative relay encoded by exon-14a/c play a key role in regulating the ATPase activity of FL1-HMM and AB4-HMM.
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Affiliation(s)
- Jie Hao
- State Key Laboratory of Integrated Management of Insect Pests and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, China
| | - Chang Liu
- State Key Laboratory of Integrated Management of Insect Pests and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Ning Zhang
- State Key Laboratory of Integrated Management of Insect Pests and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, China
| | - Jing Li
- State Key Laboratory of Integrated Management of Insect Pests and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, China
| | - Tong Ni
- State Key Laboratory of Integrated Management of Insect Pests and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, China
| | - Mingbo Qu
- School of Bioengeering, Dalian University of Technology, Dalian, China
| | - Xiang-Dong Li
- State Key Laboratory of Integrated Management of Insect Pests and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China
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2
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Miyoshi T, Belyantseva IA, Sajeevadathan M, Friedman TB. Pathophysiology of human hearing loss associated with variants in myosins. Front Physiol 2024; 15:1374901. [PMID: 38562617 PMCID: PMC10982375 DOI: 10.3389/fphys.2024.1374901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2024] [Accepted: 02/21/2024] [Indexed: 04/04/2024] Open
Abstract
Deleterious variants of more than one hundred genes are associated with hearing loss including MYO3A, MYO6, MYO7A and MYO15A and two conventional myosins MYH9 and MYH14. Variants of MYO7A also manifest as Usher syndrome associated with dysfunction of the retina and vestibule as well as hearing loss. While the functions of MYH9 and MYH14 in the inner ear are debated, MYO3A, MYO6, MYO7A and MYO15A are expressed in inner ear hair cells along with class-I myosin MYO1C and are essential for developing and maintaining functional stereocilia on the apical surface of hair cells. Stereocilia are large, cylindrical, actin-rich protrusions functioning as biological mechanosensors to detect sound, acceleration and posture. The rigidity of stereocilia is sustained by highly crosslinked unidirectionally-oriented F-actin, which also provides a scaffold for various proteins including unconventional myosins and their cargo. Typical myosin molecules consist of an ATPase head motor domain to transmit forces to F-actin, a neck containing IQ-motifs that bind regulatory light chains and a tail region with motifs recognizing partners. Instead of long coiled-coil domains characterizing conventional myosins, the tails of unconventional myosins have various motifs to anchor or transport proteins and phospholipids along the F-actin core of a stereocilium. For these myosins, decades of studies have elucidated their biochemical properties, interacting partners in hair cells and variants associated with hearing loss. However, less is known about how myosins traffic in a stereocilium using their motor function, and how each variant correlates with a clinical condition including the severity and onset of hearing loss, mode of inheritance and presence of symptoms other than hearing loss. Here, we cover the domain structures and functions of myosins associated with hearing loss together with advances, open questions about trafficking of myosins in stereocilia and correlations between hundreds of variants in myosins annotated in ClinVar and the corresponding deafness phenotypes.
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Affiliation(s)
- Takushi Miyoshi
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, United States
- Division of Molecular and Integrative Physiology, Department of Biomedical Sciences, Southern Illinois University School of Medicine, Carbondale, IL, United States
| | - Inna A. Belyantseva
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, United States
| | - Mrudhula Sajeevadathan
- Division of Molecular and Integrative Physiology, Department of Biomedical Sciences, Southern Illinois University School of Medicine, Carbondale, IL, United States
| | - Thomas B. Friedman
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, MD, United States
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3
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Cirilo JA, Liao X, Perrin BJ, Yengo CM. The dynamics of actin protrusions can be controlled by tip-localized myosin motors. J Biol Chem 2024; 300:105516. [PMID: 38042485 PMCID: PMC10801316 DOI: 10.1016/j.jbc.2023.105516] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 11/20/2023] [Accepted: 11/22/2023] [Indexed: 12/04/2023] Open
Abstract
Class III myosins localize to inner ear hair cell stereocilia and are thought to be crucial for stereocilia length regulation. Mutations within the motor domain of MYO3A that disrupt its intrinsic motor properties have been associated with non-syndromic hearing loss, suggesting that the motor properties of MYO3A are critical for its function within stereocilia. In this study, we investigated the impact of a MYO3A hearing loss mutation, H442N, using both in vitro motor assays and cell biological studies. Our results demonstrate the mutation causes a dramatic increase in intrinsic motor properties, actin-activated ATPase and in vitro actin gliding velocity, as well as an increase in actin protrusion extension velocity. We propose that both "gain of function" and "loss of function" mutations in MYO3A can impair stereocilia length regulation, which is crucial for stereocilia formation during development and normal hearing. Furthermore, we generated chimeric MYO3A constructs that replace the MYO3A motor and neck domain with the motor and neck domain of other myosins. We found that duty ratio, fraction of ATPase cycle myosin is strongly bound to actin, is a critical motor property that dictates the ability to tip localize within filopodia. In addition, in vitro actin gliding velocities correlated extremely well with filopodial extension velocities over a wide range of gliding and extension velocities. Taken together, our data suggest a model in which tip-localized myosin motors exert force that slides the membrane tip-ward, which can combat membrane tension and enhance the actin polymerization rate that ultimately drives protrusion elongation.
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Affiliation(s)
- Joseph A Cirilo
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, Pennsylvania, USA
| | - Xiayi Liao
- Department of Biology, Indiana University - Purdue University, Indianapolis, Indiana, USA
| | - Benjamin J Perrin
- Department of Biology, Indiana University - Purdue University, Indianapolis, Indiana, USA
| | - Christopher M Yengo
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, Pennsylvania, USA.
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4
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Das S, Mallick D, Sarkar S, Billington N, Sellers JR, Jana SS. A brain specific alternatively spliced isoform of nonmuscle myosin IIA lacks its mechanoenzymatic activities. J Biol Chem 2023; 299:105143. [PMID: 37562567 PMCID: PMC10480317 DOI: 10.1016/j.jbc.2023.105143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2023] [Revised: 07/29/2023] [Accepted: 08/01/2023] [Indexed: 08/12/2023] Open
Abstract
Recent genomic studies reported that 90 to 95% of human genes can undergo alternative splicing, by which multiple isoforms of proteins are synthesized. However, the functional consequences of most of the isoforms are largely unknown. Here, we report a novel alternatively spliced isoform of nonmuscle myosin IIA (NM IIA), called NM IIA2, which is generated by the inclusion of 21 amino acids near the actin-binding region (loop 2) of the head domain of heavy chains. Expression of NM IIA2 is found exclusively in the brain tissue, where it reaches a maximum level at 24 h during the circadian rhythm. The actin-dependent Mg2+-ATPase activity and in vitro motility assays reveal that NM IIA2 lacks its motor activities but localizes with actin filaments in cells. Interestingly, NM IIA2 can also make heterofilaments with NM IIA0 (noninserted isoform of NM IIA) and can retard the in vitro motility of NM IIA, when the two are mixed. Altogether, our findings provide the functional importance of a previously unknown alternatively spliced isoform, NM IIA2, and its potential physiological role in regulating NM IIA activity in the brain.
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Affiliation(s)
- Samprita Das
- School of Biological Sciences, Indian Association for the Cultivation of Science, Kolkata, West Bengal, India
| | - Ditipriya Mallick
- School of Biological Sciences, Indian Association for the Cultivation of Science, Kolkata, West Bengal, India
| | - Sourav Sarkar
- School of Biological Sciences, Indian Association for the Cultivation of Science, Kolkata, West Bengal, India
| | - Neil Billington
- Laboratory of Molecular Physiology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - James R Sellers
- Laboratory of Molecular Physiology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA.
| | - Siddhartha S Jana
- School of Biological Sciences, Indian Association for the Cultivation of Science, Kolkata, West Bengal, India.
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5
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Venturini C, Sáez P. A multi-scale clutch model for adhesion complex mechanics. PLoS Comput Biol 2023; 19:e1011250. [PMID: 37450544 PMCID: PMC10393167 DOI: 10.1371/journal.pcbi.1011250] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2023] [Accepted: 06/07/2023] [Indexed: 07/18/2023] Open
Abstract
Cell-matrix adhesion is a central mechanical function to a large number of phenomena in physiology and disease, including morphogenesis, wound healing, and tumor cell invasion. Today, how single cells respond to different extracellular cues has been comprehensively studied. However, how the mechanical behavior of the main individual molecules that form an adhesion complex cooperatively responds to force within the adhesion complex is still poorly understood. This is a key aspect of cell adhesion because how these cell adhesion molecules respond to force determines not only cell adhesion behavior but, ultimately, cell function. To answer this question, we develop a multi-scale computational model for adhesion complexes mechanics. We extend the classical clutch hypothesis to model individual adhesion chains made of a contractile actin network, a talin rod, and an integrin molecule that binds at individual adhesion sites on the extracellular matrix. We explore several scenarios of integrins dynamics and analyze the effects of diverse extracellular matrices on the behavior of the adhesion molecules and on the whole adhesion complex. Our results describe how every single component of the adhesion chain mechanically responds to the contractile actomyosin force and show how they control the traction forces exerted by the cell on the extracellular space. Importantly, our computational results agree with previous experimental data at the molecular and cellular levels. Our multi-scale clutch model presents a step forward not only to further understand adhesion complexes mechanics but also to impact, e.g., the engineering of biomimetic materials, tissue repairment, or strategies to arrest tumor progression.
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Affiliation(s)
- Chiara Venturini
- Laboratori de Càlcul Numèric (LaCaN), Universitat Politècnica de Catalunya, Barcelona, Spain
| | - Pablo Sáez
- Laboratori de Càlcul Numèric (LaCaN), Universitat Politècnica de Catalunya, Barcelona, Spain
- E.T.S. de Ingeniería de Caminos, Universitat Politècnica de Catalunya, Barcelona, Spain
- Institut de Matemàtiques de la UPC-BarcelonaTech (IMTech), Universitat Politècnica de Catalunya, Barcelona, Spain
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6
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D’Arcy BR, Lennox AL, Manso Musso C, Bracher A, Escobar-Tomlienovich C, Perez-Sanchez S, Silver DL. Non-muscle myosins control radial glial basal endfeet to mediate interneuron organization. PLoS Biol 2023; 21:e3001926. [PMID: 36854011 PMCID: PMC9974137 DOI: 10.1371/journal.pbio.3001926] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2022] [Accepted: 01/17/2023] [Indexed: 03/02/2023] Open
Abstract
Radial glial cells (RGCs) are essential for the generation and organization of neurons in the cerebral cortex. RGCs have an elongated bipolar morphology with basal and apical endfeet that reside in distinct niches. Yet, how this subcellular compartmentalization of RGCs controls cortical development is largely unknown. Here, we employ in vivo proximity labeling, in the mouse, using unfused BirA to generate the first subcellular proteome of RGCs and uncover new principles governing local control of cortical development. We discover a cohort of proteins that are significantly enriched in RGC basal endfeet, with MYH9 and MYH10 among the most abundant. Myh9 and Myh10 transcripts also localize to endfeet with distinct temporal dynamics. Although they each encode isoforms of non-muscle myosin II heavy chain, Myh9 and Myh10 have drastically different requirements for RGC integrity. Myh9 loss from RGCs decreases branching complexity and causes endfoot protrusion through the basement membrane. In contrast, Myh10 controls endfoot adhesion, as mutants have unattached apical and basal endfeet. Finally, we show that Myh9- and Myh10-mediated regulation of RGC complexity and endfoot position non-cell autonomously controls interneuron number and organization in the marginal zone. Our study demonstrates the utility of in vivo proximity labeling for dissecting local control of complex systems and reveals new mechanisms for dictating RGC integrity and cortical architecture.
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Affiliation(s)
- Brooke R. D’Arcy
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, United States of America
| | - Ashley L. Lennox
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, United States of America
| | - Camila Manso Musso
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, United States of America
| | - Annalise Bracher
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, United States of America
| | - Carla Escobar-Tomlienovich
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, United States of America
| | - Stephany Perez-Sanchez
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, United States of America
| | - Debra L. Silver
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, United States of America
- Department of Cell Biology, Duke University Medical Center, Durham, North Carolina, United States of America
- Department of Neurobiology, Duke University Medical Center, Durham, North Carolina, United States of America
- Duke Institute for Brain Sciences, Duke University Medical Center, Durham, North Carolina, United States of America
- Duke Regeneration Center, Duke University Medical Center, Durham, North Carolina, United States of America
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7
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Weißenbruch K, Fladung M, Grewe J, Baulesch L, Schwarz US, Bastmeyer M. Nonmuscle myosin IIA dynamically guides regulatory light chain phosphorylation and assembly of nonmuscle myosin IIB. Eur J Cell Biol 2022; 101:151213. [DOI: 10.1016/j.ejcb.2022.151213] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Revised: 02/16/2022] [Accepted: 02/28/2022] [Indexed: 01/27/2023] Open
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8
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Discovery of ultrafast myosin, its amino acid sequence, and structural features. Proc Natl Acad Sci U S A 2022; 119:2120962119. [PMID: 35173046 PMCID: PMC8872768 DOI: 10.1073/pnas.2120962119] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/05/2022] [Indexed: 11/18/2022] Open
Abstract
Cytoplasmic streaming with extremely high velocity (∼70 μm s-1) occurs in cells of the characean algae (Chara). Because cytoplasmic streaming is caused by myosin XI, it has been suggested that a myosin XI with a velocity of 70 μm s-1, the fastest myosin measured so far, exists in Chara cells. However, the velocity of the previously cloned Chara corallina myosin XI (CcXI) was about 20 μm s-1, one-third of the cytoplasmic streaming velocity in Chara Recently, the genome sequence of Chara braunii has been published, revealing that this alga has four myosin XI genes. We cloned these four myosin XI (CbXI-1, 2, 3, and 4) and measured their velocities. While the velocities of CbXI-3 and CbXI-4 motor domains (MDs) were similar to that of CcXI MD, the velocities of CbXI-1 and CbXI-2 MDs were 3.2 times and 2.8 times faster than that of CcXI MD, respectively. The velocity of chimeric CbXI-1, a functional, full-length CbXI-1 construct, was 60 μm s-1 These results suggest that CbXI-1 and CbXI-2 would be the main contributors to cytoplasmic streaming in Chara cells and show that these myosins are ultrafast myosins with a velocity 10 times faster than fast skeletal muscle myosins in animals. We also report an atomic structure (2.8-Å resolution) of myosin XI using X-ray crystallography. Based on this crystal structure and the recently published cryo-electron microscopy structure of acto-myosin XI at low resolution (4.3-Å), it appears that the actin-binding region contributes to the fast movement of Chara myosin XI. Mutation experiments of actin-binding surface loops support this hypothesis.
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9
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Weißenbruch K, Grewe J, Hippler M, Fladung M, Tremmel M, Stricker K, Schwarz US, Bastmeyer M. Distinct roles of nonmuscle myosin II isoforms for establishing tension and elasticity during cell morphodynamics. eLife 2021; 10:71888. [PMID: 34374341 PMCID: PMC8391736 DOI: 10.7554/elife.71888] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Accepted: 08/09/2021] [Indexed: 12/29/2022] Open
Abstract
Nonmuscle myosin II (NM II) is an integral part of essential cellular processes, including adhesion and migration. Mammalian cells express up to three isoforms termed NM IIA, B, and C. We used U2OS cells to create CRISPR/Cas9-based knockouts of all three isoforms and analyzed the phenotypes on homogenously coated surfaces, in collagen gels, and on micropatterned substrates. In contrast to homogenously coated surfaces, a structured environment supports a cellular phenotype with invaginated actin arcs even in the absence of NM IIA-induced contractility. A quantitative shape analysis of cells on micropatterns combined with a scale-bridging mathematical model reveals that NM IIA is essential to build up cellular tension during initial stages of force generation, while NM IIB is necessary to elastically stabilize NM IIA-generated tension. A dynamic cell stretch/release experiment in a three-dimensional scaffold confirms these conclusions and in addition reveals a novel role for NM IIC, namely the ability to establish tensional homeostasis.
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Affiliation(s)
- Kai Weißenbruch
- Zoological Institute, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany.,Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
| | - Justin Grewe
- Institute for Theoretical Physics, University of Heidelberg, Heidelberg, Germany.,BioQuant-Center for Quantitative Biology, University of Heidelberg, Heidelberg, Germany
| | - Marc Hippler
- Zoological Institute, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany.,Institute of Applied Physics, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
| | - Magdalena Fladung
- Zoological Institute, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
| | - Moritz Tremmel
- Zoological Institute, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
| | - Kathrin Stricker
- Zoological Institute, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
| | - Ulrich Sebastian Schwarz
- Institute for Theoretical Physics, University of Heidelberg, Heidelberg, Germany.,BioQuant-Center for Quantitative Biology, University of Heidelberg, Heidelberg, Germany
| | - Martin Bastmeyer
- Zoological Institute, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany.,Institute for Biological and Chemical Systems - Biological Information Processing (IBCS-BIP), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
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10
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Ecsédi P, Billington N, Pálfy G, Gógl G, Kiss B, Bulyáki É, Bodor A, Sellers JR, Nyitray L. Multiple S100 protein isoforms and C-terminal phosphorylation contribute to the paralog-selective regulation of nonmuscle myosin 2 filaments. J Biol Chem 2018; 293:14850-14867. [PMID: 30087119 PMCID: PMC6153290 DOI: 10.1074/jbc.ra118.004277] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2018] [Revised: 08/06/2018] [Indexed: 12/27/2022] Open
Abstract
Nonmuscle myosin 2 (NM2) has three paralogs in mammals, NM2A, NM2B, and NM2C, which have both unique and overlapping functions in cell migration, formation of cell-cell adhesions, and cell polarity. Their assembly into homo- and heterotypic bipolar filaments in living cells is primarily regulated by phosphorylation of the N-terminally bound regulatory light chain. Here, we present evidence that the equilibrium between these filaments and single NM2A and NM2B molecules can be controlled via S100 calcium-binding protein interactions and phosphorylation at the C-terminal end of the heavy chains. Furthermore, we show that in addition to S100A4, other members of the S100 family can also mediate disassembly of homotypic NM2A filaments. Importantly, these proteins can selectively remove NM2A molecules from heterotypic filaments. We also found that tail phosphorylation (at Ser-1956 and Ser-1975) of NM2B by casein kinase 2, as well as phosphomimetic substitutions at sites targeted by protein kinase C (PKC) and transient receptor potential cation channel subfamily M member 7 (TRPM7), down-regulates filament assembly in an additive fashion. Tail phosphorylation of NM2A had a comparatively minor effect on filament stability. S100 binding and tail phosphorylation therefore preferentially disassemble NM2A and NM2B, respectively. These two distinct mechanisms are likely to contribute to the temporal and spatial sorting of the two NM2 paralogs within heterotypic filaments. The existence of multiple NM2A-depolymerizing S100 paralogs offers the potential for diverse regulatory inputs modulating NM2A filament disassembly in cells and provides functional redundancy under both physiological and pathological conditions.
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Affiliation(s)
| | - Neil Billington
- the Laboratory of Physiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892
| | - Gyula Pálfy
- the Laboratory of Structural Chemistry and Biology, Institute of Chemistry, and
| | | | | | - Éva Bulyáki
- From the Department of Biochemistry
- the ELTE NAP Neuroimmunology Research Group, Department of Biochemistry, ELTE Eötvös Loránd University, Pázmány Péter Sétány 1/C, 1117 Budapest, Hungary and
| | - Andrea Bodor
- the Laboratory of Structural Chemistry and Biology, Institute of Chemistry, and
| | - James R Sellers
- the Laboratory of Physiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892
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11
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Melli L, Billington N, Sun SA, Bird JE, Nagy A, Friedman TB, Takagi Y, Sellers JR. Bipolar filaments of human nonmuscle myosin 2-A and 2-B have distinct motile and mechanical properties. eLife 2018; 7:32871. [PMID: 29419377 PMCID: PMC5829915 DOI: 10.7554/elife.32871] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Accepted: 01/22/2018] [Indexed: 12/26/2022] Open
Abstract
Nonmusclemyosin 2 (NM-2) powers cell motility and tissue morphogenesis by assembling into bipolar filaments that interact with actin. Although the enzymatic properties of purified NM-2 motor fragments have been determined, the emergent properties of filament ensembles are unknown. Using single myosin filament in vitro motility assays, we report fundamental differences in filaments formed of different NM-2 motors. Filaments consisting of NM2-B moved processively along actin, while under identical conditions, NM2-A filaments did not. By more closely mimicking the physiological milieu, either by increasing solution viscosity or by co-polymerization with NM2-B, NM2-A containing filaments moved processively. Our data demonstrate that both the kinetic and mechanical properties of these two myosins, in addition to the stochiometry of NM-2 subunits, can tune filament mechanical output. We propose altering NM-2 filament composition is a general cellular strategy for tailoring force production of filaments to specific functions, such as maintaining tension or remodeling actin.
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Affiliation(s)
- Luca Melli
- Cell Biology and Physiology Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, United States
| | - Neil Billington
- Cell Biology and Physiology Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, United States
| | - Sara A Sun
- Cell Biology and Physiology Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, United States
| | - Jonathan E Bird
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, United States
| | - Attila Nagy
- Vaccine Production Program Laboratory, National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Gaithersburg, United States
| | - Thomas B Friedman
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, United States
| | - Yasuharu Takagi
- Cell Biology and Physiology Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, United States
| | - James R Sellers
- Cell Biology and Physiology Center, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, United States
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12
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Effect of ATP and regulatory light-chain phosphorylation on the polymerization of mammalian nonmuscle myosin II. Proc Natl Acad Sci U S A 2017; 114:E6516-E6525. [PMID: 28739905 DOI: 10.1073/pnas.1702375114] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Addition of 1 mM ATP substantially reduces the light scattering of solutions of polymerized unphosphorylated nonmuscle myosin IIs (NM2s), and this is reversed by phosphorylation of the regulatory light chain (RLC). It has been proposed that these changes result from substantial depolymerization of unphosphorylated NM2 filaments to monomers upon addition of ATP, and filament repolymerization upon RLC-phosphorylation. We now show that the differences in myosin monomer concentration of RLC-unphosphorylated and -phosphorylated recombinant mammalian NM2A, NM2B, and NM2C polymerized in the presence of ATP are much too small to explain their substantial differences in light scattering. Rather, we find that the decrease in light scattering upon addition of ATP to polymerized unphosphorylated NM2s correlates with the formation of dimers, tetramers, and hexamers, in addition to monomers, an increase in length, and decrease in width of the bare zones of RLC-unphosphorylated filaments. Both effects of ATP addition are reversed by phosphorylation of the RLC. Our data also suggest that, contrary to previous models, assembly of RLC-phosphorylated NM2s at physiological ionic strength proceeds from folded monomers to folded antiparallel dimers, tetramers, and hexamers that unfold and polymerize into antiparallel filaments. This model could explain the dynamic relocalization of NM2 filaments in vivo by dephosphorylation of RLC-phosphorylated filaments, disassembly of the dephosphorylated filaments to folded monomers, dimers, and small oligomers, followed by diffusion of these species, and reassembly of filaments at the new location following rephosphorylation of the RLC.
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13
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Xu GK, Li B, Feng XQ, Gao H. A Tensegrity Model of Cell Reorientation on Cyclically Stretched Substrates. Biophys J 2016; 111:1478-1486. [PMID: 27705770 PMCID: PMC5052513 DOI: 10.1016/j.bpj.2016.08.036] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Revised: 07/09/2016] [Accepted: 08/31/2016] [Indexed: 01/16/2023] Open
Abstract
Deciphering the mechanisms underlying the high sensitivity of cells to mechanical microenvironments is crucial for understanding many physiological and pathological processes, e.g., stem cell differentiation and cancer cell metastasis. Here, a cytoskeletal tensegrity model is proposed to study the reorientation of polarized cells on a substrate under biaxial cyclic deformation. The model consists of four bars, representing the longitudinal stress fibers and lateral actin network, and eight strings, denoting the microfilaments. It is found that the lateral bars in the tensegrity, which have been neglected in most of the existing models, can play a vital role in regulating the cellular orientation. The steady orientation of cells can be quantitatively determined by the geometric dimensions and elastic properties of the tensegrity elements, as well as the frequency and biaxial ratio of the cyclic stretches. It is shown that this tensegrity model can reproduce all available experimental observations. For example, the dynamics of cell reorientation is captured by an exponential scaling law with a characteristic time that is independent of the loading frequency at high frequencies and scales inversely with the square of the strain amplitude. This study suggests that tensegrity type models may be further developed to understand cellular responses to mechanical microenvironments and provide guidance for engineering delicate cellular mechanosensing systems.
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Affiliation(s)
- Guang-Kui Xu
- International Center for Applied Mechanics, State Key Laboratory for Strength and Vibration of Mechanical Structures, School of Aerospace, Xi'an Jiaotong University, Xi'an, China.
| | - Bo Li
- Institute of Biomechanics and Medical Engineering, Department of Engineering Mechanics, Tsinghua University, Beijing, China
| | - Xi-Qiao Feng
- Institute of Biomechanics and Medical Engineering, Department of Engineering Mechanics, Tsinghua University, Beijing, China.
| | - Huajian Gao
- School of Engineering, Brown University, Providence, Rhode Island
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14
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Heissler SM, Sellers JR. Various Themes of Myosin Regulation. J Mol Biol 2016; 428:1927-46. [PMID: 26827725 DOI: 10.1016/j.jmb.2016.01.022] [Citation(s) in RCA: 84] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2015] [Revised: 01/12/2016] [Accepted: 01/19/2016] [Indexed: 10/24/2022]
Abstract
Members of the myosin superfamily are actin-based molecular motors that are indispensable for cellular homeostasis. The vast functional and structural diversity of myosins accounts for the variety and complexity of the underlying allosteric regulatory mechanisms that determine the activation or inhibition of myosin motor activity and enable precise timing and spatial aspects of myosin function at the cellular level. This review focuses on the molecular basis of posttranslational regulation of eukaryotic myosins from different classes across species by allosteric intrinsic and extrinsic effectors. First, we highlight the impact of heavy and light chain phosphorylation. Second, we outline intramolecular regulatory mechanisms such as autoinhibition and subsequent activation. Third, we discuss diverse extramolecular allosteric mechanisms ranging from actin-linked regulatory mechanisms to myosin:cargo interactions. At last, we briefly outline the allosteric regulation of myosins with synthetic compounds.
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Affiliation(s)
- Sarah M Heissler
- Laboratory of Molecular Physiology, National Heart, Lung and Blood Institute, National Institutes of Health, 50 South Drive, B50/3529, Bethesda, MD 20892-8015, USA.
| | - James R Sellers
- Laboratory of Molecular Physiology, National Heart, Lung and Blood Institute, National Institutes of Health, 50 South Drive, B50/3529, Bethesda, MD 20892-8015, USA
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15
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Lehtimäki J, Hakala M, Lappalainen P. Actin Filament Structures in Migrating Cells. Handb Exp Pharmacol 2016; 235:123-152. [PMID: 27469496 DOI: 10.1007/164_2016_28] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Cell migration is necessary for several developmental processes in multicellular organisms. Furthermore, many physiological processes such as wound healing and immunological events in adult animals are dependent on cell migration. Consequently, defects in cell migration are linked to various diseases including immunological disorders as well as cancer progression and metastasis formation. Cell migration is driven by specific protrusive and contractile actin filament structures, but the types and relative contributions of these actin filament arrays vary depending on the cell type and the environment of the cell. In this chapter, we introduce the most important actin filament structures that contribute to mesenchymal and amoeboid cell migration modes and discuss the mechanisms by which the assembly and turnover of these structures are controlled by various actin-binding proteins.
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Affiliation(s)
- Jaakko Lehtimäki
- Institute of Biotechnology, University of Helsinki, 56, 00014, Helsinki, Finland
| | - Markku Hakala
- Institute of Biotechnology, University of Helsinki, 56, 00014, Helsinki, Finland
| | - Pekka Lappalainen
- Institute of Biotechnology, University of Helsinki, 56, 00014, Helsinki, Finland.
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16
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How actin initiates the motor activity of Myosin. Dev Cell 2015; 33:401-12. [PMID: 25936506 DOI: 10.1016/j.devcel.2015.03.025] [Citation(s) in RCA: 87] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2014] [Revised: 02/23/2015] [Accepted: 03/30/2015] [Indexed: 11/22/2022]
Abstract
Fundamental to cellular processes are directional movements driven by molecular motors. A common theme for these and other molecular machines driven by ATP is that controlled release of hydrolysis products is essential for using the chemical energy efficiently. Mechanochemical transduction by myosin motors on actin is coupled to unknown structural changes that result in the sequential release of inorganic phosphate (Pi) and MgADP. We present here a myosin structure possessing an actin-binding interface and a tunnel (back door) that creates an escape route for Pi with a minimal rotation of the myosin lever arm that drives movements. We propose that this state represents the beginning of the powerstroke on actin and that Pi translocation from the nucleotide pocket triggered by actin binding initiates myosin force generation. This elucidates how actin initiates force generation and movement and may represent a strategy common to many molecular machines.
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17
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An BC, Sakai T, Komaba S, Kishi H, Kobayashi S, Kim JY, Ikebe R, Ikebe M. Phosphorylation of the kinase domain regulates autophosphorylation of myosin IIIA and its translocation in microvilli. Biochemistry 2014; 53:7835-45. [PMID: 25402663 PMCID: PMC4270376 DOI: 10.1021/bi501247z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
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Motor activity of myosin III is regulated
by autophosphorylation.
To investigate the role of the kinase activity on the transporter
function of myosin IIIA (Myo3A), we identified the phosphorylation
sites of kinase domain (KD), which is responsible for the regulation
of kinase activity and thus motor function. Using mass spectrometry,
we identified six phosphorylation sites in the KD, which are highly
conserved among class III myosins and Ste20-related misshapen (Msn)
kinases. Two predominant sites, Thr184 and Thr188, in KD are important for phosphorylation of the KD as well as the
motor domain, which regulates the affinity for actin. In the Caco2
cells, the full-length human Myo3A (hMyo3AFull) markedly enlarged
the microvilli, although it did not show discrete localization within
the microvilli. On the other hand, hMyo3AFull(T184A) and hMyo3AFull(T188A)
both showed clear localization at the microvilli tips. Our results
suggest that Myo3A induces large actin bundle formation to form microvilli,
and phosphorylation of KD at Thr184 and Thr188 is critical for the kinase activity of Myo3A, and regulation of
Myo3A translocation to the tip of microvilli. Retinal extracts potently
dephosphorylate both KD and motor domain without IQ motifs (MDIQo),
which was inhibited by okadaic acid (OA) with nanomolar range and
by tautomycetin (TMC) with micromolar range. The results suggest that
Myo3A phosphatase is protein phosphatase type 2A (PP2A). Supporting
this result, recombinant PP2Ac potently dephosphorylates both KD and
MDIQo. We propose that the phosphorylation–dephosphorylation
mechanism plays an essential role in mediating the transport and actin
bundle formation and stability functions of hMyo3A.
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Affiliation(s)
- Byung Chull An
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School , Worcester, Massachusetts 01605, United States
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18
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Barua B, Nagy A, Sellers JR, Hitchcock-DeGregori SE. Regulation of nonmuscle myosin II by tropomyosin. Biochemistry 2014; 53:4015-24. [PMID: 24873380 PMCID: PMC4075986 DOI: 10.1021/bi500162z] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
![]()
The
actin cytoskeleton carries out cellular functions, including
division, migration, adhesion, and intracellular transport, that require
a variety of actin binding proteins, including myosins. Our focus
here is on class II nonmuscle myosin isoforms, NMIIA, NMIIB, and NMIIC,
and their regulation by the actin binding protein, tropomyosin. NMII
myosins are localized to different populations of stress fibers and
the contractile ring, structures involved in force generation required
for cell migration, adhesion, and cytokinesis. The stress fibers and
contractile ring that contain NMII myosins also contain tropomyosin.
Four mammalian genes encode more than 40 tropomyosins. Tropomyosins
inhibit or activate actomyosin MgATPase and motility depending on
the myosin and tropomyosin isoform. In vivo, tropomyosins
play a role in cell migration, adhesion, cytokinesis, and NMII isoform
localization in an isoform-specific manner. We postulate that the
isoform-specific tropomyosin localization and effect on NMII isoform
localization reflect modulation of NMII actomyosin kinetics and motile
function. In this study, we compare the ability of different tropomyosin
isoforms to support actin filament motility with NMIIA, NMIIB, and
NMIIC as well as skeletal muscle myosin. Tropomyosins activated, inhibited,
or had no effect on motility depending on the myosin, indicating that
the myosin isoform is the primary determinant of the isoform-specific
effect of tropomyosin on actomyosin regulation. Activation of motility
of nonmuscle tropomyosin–actin filaments by NMII myosin correlates
with an increased Vmax of the myosin MgATPase,
implying a direct effect on the myosin MgATPase, in contrast to the
skeletal tropomyosin–actin filament that has no effect on the Vmax or maximal filament velocity.
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Affiliation(s)
- Bipasha Barua
- Department of Pathology and Laboratory Medicine, Robert Wood Johnson Medical School, Rutgers University , Piscataway, New Jersey 08854, United States
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19
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Myosin-10 produces its power-stroke in two phases and moves processively along a single actin filament under low load. Proc Natl Acad Sci U S A 2014; 111:E1833-42. [PMID: 24753602 DOI: 10.1073/pnas.1320122111] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Myosin-10 is an actin-based molecular motor that participates in essential intracellular processes such as filopodia formation/extension, phagocytosis, cell migration, and mitotic spindle maintenance. To study this motor protein's mechano-chemical properties, we used a recombinant, truncated form of myosin-10 consisting of the first 936 amino acids, followed by a GCN4 leucine zipper motif, to force dimerization. Negative-stain electron microscopy reveals that the majority of molecules are dimeric with a head-to-head contour distance of ∼50 nm. In vitro motility assays show that myosin-10 moves actin filaments smoothly with a velocity of ∼310 nm/s. Steady-state and transient kinetic analysis of the ATPase cycle shows that the ADP release rate (∼13 s(-1)) is similar to the maximum ATPase activity (∼12-14 s(-1)) and therefore contributes to rate limitation of the enzymatic cycle. Single molecule optical tweezers experiments show that under intermediate load (∼0.5 pN), myosin-10 interacts intermittently with actin and produces a power stroke of ∼17 nm, composed of an initial 15-nm and subsequent 2-nm movement. At low optical trap loads, we observed staircase-like processive movements of myosin-10 interacting with the actin filament, consisting of up to six ∼35-nm steps per binding interaction. We discuss the implications of this load-dependent processivity of myosin-10 as a filopodial transport motor.
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20
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Billington N, Wang A, Mao J, Adelstein RS, Sellers JR. Characterization of three full-length human nonmuscle myosin II paralogs. J Biol Chem 2013; 288:33398-410. [PMID: 24072716 DOI: 10.1074/jbc.m113.499848] [Citation(s) in RCA: 140] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Nonmuscle myosin IIs (NM IIs) are a group of molecular motors involved in a wide variety of cellular processes including cytokinesis, migration, and control of cell morphology. There are three paralogs of the NM II heavy chain in humans (IIA, IIB, and IIC), each encoded by a separate gene. These paralogs are expressed at different levels according to cell type and have different roles and intracellular distributions in vivo. Most previous studies on NM II used tissue-purified protein or expressed fragments of the molecule, which presents potential drawbacks for characterizing individual paralogs of the intact protein in vitro. To circumvent current limitations and approach their native properties, we have successfully expressed and purified the three full-length human NM II proteins with their light chains, using the baculovirus/Sf9 system. The enzymatic and structural properties of the three paralogs were characterized. Although each NM II is capable of forming bipolar filaments, those formed by IIC tend to contain fewer constituent molecules than those of IIA and IIB. All paralogs adopt the compact conformation in the presence of ATP. Phosphorylation of the regulatory light chain leads to assembly into filaments, which bind to actin in the presence of ATP. The nature of interactions with actin filaments is shown with different paralogs exhibiting different actin binding behaviors under equivalent conditions. The data show that although NM IIA and IIB form filaments with similar properties, NM IIC forms filaments that are less well suited to roles such as tension maintenance within the cell.
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21
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Ackermann MA, Patel PD, Valenti J, Takagi Y, Homsher E, Sellers JR, Kontrogianni-Konstantopoulos A. Loss of actomyosin regulation in distal arthrogryposis myopathy due to mutant myosin binding protein-C slow. FASEB J 2013; 27:3217-28. [PMID: 23657818 DOI: 10.1096/fj.13-228882] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Myosin binding protein C (MyBP-C) is expressed in striated muscles, where it plays key roles in the modulation of actomyosin cross-bridges. Slow MyBP-C (sMyBP-C) consists of multiple variants sharing common domains but also containing unique segments within the NH2 and COOH termini. Two missense mutations in the NH2 terminus (W236R) and COOH terminus (Y856H) of sMyBP-C have been causally linked to the development of distal arthrogryposis-1 (DA-1), a severe skeletal muscle disorder. Using a combination of in vitro binding and motility assays, we show that the COOH terminus mediates binding of sMyBP-C to thick filaments, while the NH2 terminus modulates the formation of actomyosin cross-bridges in a variant-specific manner. Consistent with this, a recombinant NH2-terminal peptide that excludes residues 34-59 reduces the sliding velocity of actin filaments past myosin heads from 9.0 ± 1.3 to 5.7 ± 1.0 μm/s at 0.1 μM, while a recombinant peptide that excludes residues 21-59 fails to do so. Notably, the actomyosin regulatory properties of sMyBP-C are completely abolished by the presence of the DA-1 mutations. In summary, our studies are the first to show that the NH2 and COOH termini of sMyBP-C have distinct functions, which are regulated by differential splicing, and are compromized by the presence of missense point mutations linked to muscle disease.
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Affiliation(s)
- Maegen A Ackermann
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 108 N. Greene St, Baltimore, MD 21201, USA
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22
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Guzik-Lendrum S, Heissler SM, Billington N, Takagi Y, Yang Y, Knight PJ, Homsher E, Sellers JR. Mammalian myosin-18A, a highly divergent myosin. J Biol Chem 2013; 288:9532-48. [PMID: 23382379 DOI: 10.1074/jbc.m112.441238] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The Mus musculus myosin-18A gene is expressed as two alternatively spliced isoforms, α and β, with reported roles in Golgi localization, in maintenance of cytoskeleton, and as receptors for immunological surfactant proteins. Both myosin-18A isoforms feature a myosin motor domain, a single predicted IQ motif, and a long coiled-coil reminiscent of myosin-2. The myosin-18Aα isoform, additionally, has an N-terminal PDZ domain. Recombinant heavy meromyosin- and subfragment-1 (S1)-like constructs for both myosin-18Aα and -18β species were purified from the baculovirus/Sf9 cell expression system. These constructs bound both essential and regulatory light chains, indicating an additional noncanonical light chain binding site in the neck. Myosin-18Aα-S1 and -18Aβ-S1 molecules bound actin weakly with Kd values of 4.9 and 54 μm, respectively. The actin binding data could be modeled by assuming an equilibrium between two myosin conformations, a competent and an incompetent form to bind actin. Actin binding was unchanged by presence of nucleotide. Both myosin-18A isoforms bound N-methylanthraniloyl-nucleotides, but the rate of ATP hydrolysis was very slow (<0.002 s(-1)) and not significantly enhanced by actin. Phosphorylation of the regulatory light chain had no effect on ATP hydrolysis, and neither did the addition of tropomyosin or of GOLPH3, a myosin-18A binding partner. Electron microscopy of myosin-18A-S1 showed that the lever is strongly angled with respect to the long axis of the motor domain, suggesting a pre-power stroke conformation regardless of the presence of ATP. These data lead us to conclude that myosin-18A does not operate as a traditional molecular motor in cells.
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Affiliation(s)
- Stephanie Guzik-Lendrum
- Laboratory of Molecular Physiology, NHLBI, National Institutes of Health, Bethesda, MD 20892-8015, USA
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23
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Nagy A, Takagi Y, Billington N, Sun SA, Hong DKT, Homsher E, Wang A, Sellers JR. Kinetic characterization of nonmuscle myosin IIb at the single molecule level. J Biol Chem 2012; 288:709-22. [PMID: 23148220 DOI: 10.1074/jbc.m112.424671] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nonmuscle myosin IIB (NMIIB) is a cytoplasmic myosin, which plays an important role in cell motility by maintaining cortical tension. It forms bipolar thick filaments with ~14 myosin molecule dimers on each side of the bare zone. Our previous studies showed that the NMIIB is a moderately high duty ratio (~20-25%) motor. The ADP release step (~0.35 s(-1)) of NMIIB is only ~3 times faster than the rate-limiting phosphate release (0.13 ± 0.01 s(-1)). The aim of this study was to relate the known in vitro kinetic parameters to the results of single molecule experiments and to compare the kinetic and mechanical properties of single- and double-headed myosin fragments and nonmuscle IIB thick filaments. Examination of the kinetics of NMIIB interaction with actin at the single molecule level was accomplished using total internal reflection fluorescence (TIRF) with fluorescence imaging with 1-nm accuracy (FIONA) and dual-beam optical trapping. At a physiological ATP concentration (1 mm), the rate of detachment of the single-headed and double-headed molecules was similar (~0.4 s(-1)). Using optical tweezers we found that the power stroke sizes of single- and double-headed heavy meromyosin (HMM) were each ~6 nm. No signs of processive stepping at the single molecule level were observed in the case of NMIIB-HMM in optical tweezers or TIRF/in vitro motility experiments. In contrast, robust motility of individual fluorescently labeled thick filaments of full-length NMIIB was observed on actin filaments. Our results are in good agreement with the previous steady-state and transient kinetic studies and show that the individual nonprocessive nonmuscle myosin IIB molecules form a highly processive unit when polymerized into filaments.
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Affiliation(s)
- Attila Nagy
- Laboratory of Molecular Physiology, HLBI, National Institutes of Health, Bethesda, Maryland 20892, USA
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24
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Heissler SM, Manstein DJ. Nonmuscle myosin-2: mix and match. Cell Mol Life Sci 2012; 70:1-21. [PMID: 22565821 PMCID: PMC3535348 DOI: 10.1007/s00018-012-1002-9] [Citation(s) in RCA: 165] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2012] [Revised: 04/16/2012] [Accepted: 04/17/2012] [Indexed: 12/31/2022]
Abstract
Members of the nonmuscle myosin-2 (NM-2) family of actin-based molecular motors catalyze the conversion of chemical energy into directed movement and force thereby acting as central regulatory components of the eukaryotic cytoskeleton. By cyclically interacting with adenosine triphosphate and F-actin, NM-2 isoforms promote cytoskeletal force generation in established cellular processes like cell migration, shape changes, adhesion dynamics, endo- and exo-cytosis, and cytokinesis. Novel functions of the NM-2 family members in autophagy and viral infection are emerging, making NM-2 isoforms regulators of nearly all cellular processes that require the spatiotemporal organization of cytoskeletal scaffolding. Here, we assess current views about the role of NM-2 isoforms in these activities including the tight regulation of NM-2 assembly and activation through phosphorylation and how NM-2-mediated changes in cytoskeletal dynamics and mechanics affect cell physiological functions in health and disease.
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Affiliation(s)
- Sarah M. Heissler
- Institute for Biophysical Chemistry, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany
| | - Dietmar J. Manstein
- Institute for Biophysical Chemistry, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany
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25
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Dalal JS, Stevens SM, Alvarez S, Munoz N, Kempler KE, Dosé AC, Burnside B, Battelle BA. Mouse class III myosins: kinase activity and phosphorylation sites. J Neurochem 2011; 119:772-84. [PMID: 21895655 DOI: 10.1111/j.1471-4159.2011.07468.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
As class III unconventional myosins are motor proteins with an N-terminal kinase domain, it seems likely they play a role in both signaling and actin based transport. A growing body of evidence indicates that the motor functions of human class IIIA myosin, which has been implicated in progressive hearing loss, are modulated by intermolecular autophosphorylation. However, the phosphorylation sites have not been identified. We studied the kinase activity and phosphorylation sites of mouse class III myosins, mMyo3A and 3B, which are highly similar to their human orthologs. We demonstrate that the kinase domains of mMyo3A and 3B are active kinases, and that they have similar, if not identical, substrate specificities. We show that the kinase domains of these proteins autophosphorylate, and that they can phosphorylate sites within their myosin and tail domains. Using liquid chromatography-mass spectrometry, we identified phosphorylated sites in the kinase, myosin motor and tail domains of both mMyo3A and 3B. Most of the phosphorylated sites we identified and their consensus phosphorylation motifs are highly conserved among vertebrate class III myosins, including human class III myosins. Our findings are a major step toward understanding how the functions of class III myosins are regulated by phosphorylation.
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Affiliation(s)
- Jasbir S Dalal
- Department of Molecular and Cell Biology, University of California, Berkeley, California, USA
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26
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Guzik-Lendrum S, Nagy A, Takagi Y, Houdusse A, Sellers JR. Drosophila melanogaster myosin-18 represents a highly divergent motor with actin tethering properties. J Biol Chem 2011; 286:21755-66. [PMID: 21498886 PMCID: PMC3122231 DOI: 10.1074/jbc.m111.218669] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
The gene encoding Drosophila myosin-18 is complex and can potentially yield six alternatively spliced mRNAs. One of the major features of this myosin is an N-terminal PDZ domain that is included in some of the predicted alternatively spliced products. To explore the biochemical properties of this protein, we engineered two minimal motor domain (MMD)-like constructs, one that contains the N-terminal PDZ (myosin-18 M-PDZ) domain and one that does not (myosin-18 M-ΔPDZ). These two constructs were expressed in the baculovirus/Sf9 system. The results suggest that Drosophila myosin-18 is highly divergent from most other myosins in the superfamily. Neither of the MMD constructs had an actin-activated MgATPase activity, nor did they even bind ATP. Both myosin-18 M-PDZ and M-ΔPDZ proteins bound to actin with Kd values of 2.61 and 1.04 μm, respectively, but only about 50–75% of the protein bound to actin even at high actin concentrations. Unbound proteins from these actin binding assays reiterated the 60% saturation maximum, suggesting an equilibrium between actin-binding and non-actin-binding conformations of Drosophila myosin-18 in vitro. Neither the binding affinity nor the substoichiometric binding was significantly affected by ATP. Optical trapping of single molecules in three-bead assays showed short lived interactions of the myosin-18 motors with actin filaments. Combined, these data suggest that this highly divergent motor may function as an actin tethering protein.
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Affiliation(s)
- Stephanie Guzik-Lendrum
- Laboratory of Molecular Physiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892, USA
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27
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Moore SW, Roca-Cusachs P, Sheetz MP. Stretchy proteins on stretchy substrates: the important elements of integrin-mediated rigidity sensing. Dev Cell 2010; 19:194-206. [PMID: 20708583 DOI: 10.1016/j.devcel.2010.07.018] [Citation(s) in RCA: 304] [Impact Index Per Article: 21.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2010] [Revised: 06/13/2010] [Accepted: 07/16/2010] [Indexed: 01/06/2023]
Abstract
Matrix and tissue rigidity guides many cellular processes, including the differentiation of stem cells and the migration of cells in health and disease. Cells actively and transiently test rigidity using mechanisms limited by inherent physical parameters that include the strength of extracellular attachments, the pulling capacity on these attachments, and the sensitivity of the mechanotransduction system. Here, we focus on rigidity sensing mediated through the integrin family of extracellular matrix receptors and linked proteins and discuss the evidence supporting these proteins as mechanosensors.
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Affiliation(s)
- Simon W Moore
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA
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28
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Kengyel A, Wolf WA, Chisholm RL, Sellers JR. Nonmuscle myosin IIA with a GFP fused to the N-terminus of the regulatory light chain is regulated normally. J Muscle Res Cell Motil 2010; 31:163-70. [PMID: 20711642 PMCID: PMC3786345 DOI: 10.1007/s10974-010-9220-y] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2010] [Accepted: 07/08/2010] [Indexed: 10/19/2022]
Abstract
Nonmuscle myosin II plays a crucial role in a variety of cellular processes (e.g., polarity formation, cell motility, and cytokinesis). It is composed of two heavy chains, two regulatory light chains and two essential light chains. The ATPase activity of the myosin II motor domain is regulated through phosphorylation of the regulatory light chain (RLC) by myosin light chain kinase. To study myosin function and localization in cellular processes, GFP-fused RLCs are widely used; however, the exact kinetic properties of myosins with bound GFP-RLC are poorly described. More importantly, it has not been shown that a regulatory light chain fused at its N-terminus with GFP can maintain the normal phosphorylation-dependent regulation of nonmuscle myosin or serve as a substrate for myosin light chain kinase. We coexpressed N-terminal GFP-RLC with a heavy meromyosin (HMM)-like fragment of nonmuscle myosin IIA and essential light chain to characterize the phosphorylation dynamics and in vitro kinetic properties of the resulting HMM. Myosin light chain kinase phosphorylates the GFP-RLC bound to HMM IIA with the same V(max) as it does the wild type RLC bound to HMM IIA, but the K(m) is about two fold higher for the GFP fusion protein, meaning that it is a somewhat poorer substrate. The steady-state actin-activated MgATPase activity of the GFP-RLC HMM is very low in the absence of phosphorylation demonstrating that the GFP moiety does not prevent formation of the off state. The actin-activated MgATPase activity of phosphorylated GFP-RLC-HMM and is about half that of wild type phosphorylated HMM. The ability of phosphorylated GFP-RLC-HMM to move actin filaments in the actin gliding assay is also slightly compromised. These data indicate that despite some kinetic differences the N-terminal GFP fusion to the regulatory light chain is a reasonable model system for studying myosin function in vivo.
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Affiliation(s)
- Andras Kengyel
- Laboratory of Molecular Physiology, National Heart, Lung and Blood Institute, National Institutes of Health, Building 50, Room 3523, Bethesda, MD 20892, USA. Department of Biophysics, Faculty of Medicine, University of Pécs, Pécs, Hungary
| | - Wendy A. Wolf
- Center for Genetic Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
| | - Rex L. Chisholm
- Center for Genetic Medicine, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA
| | - James R. Sellers
- Laboratory of Molecular Physiology, National Heart, Lung and Blood Institute, National Institutes of Health, Building 50, Room 3523, Bethesda, MD 20892, USA
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29
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Abstract
The general structural features of the motor region of myosin superfamily members are now well established, as is a subset of the structural and kinetic transitions of the actin-myosin catalytic cycle. Not yet visualized are the structural rearrangements triggered by actin binding that are coupled to force generation and product release. In this review we describe the recent progress in understanding these missing components of the mechanism of chemomechanical transduction by myosin motors. These insights come from a combination of kinetic and single-molecule studies on multiple classes of myosins, with additional insights from contracting muscle fibers. These recent studies have explored the effects of intermediate and high loads on the kinetics of the actin-bound myosin state transitions. We also describe studies that delineate how some classes of myosin motors are adapted for processive movement on actin.
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Affiliation(s)
- H Lee Sweeney
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6085, USA.
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30
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Stachowiak MR, O'Shaughnessy B. Recoil after severing reveals stress fiber contraction mechanisms. Biophys J 2009; 97:462-71. [PMID: 19619460 DOI: 10.1016/j.bpj.2009.04.051] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2008] [Revised: 04/06/2009] [Accepted: 04/22/2009] [Indexed: 10/20/2022] Open
Abstract
Stress fibers are cellular contractile actomyosin machines central to wound healing, shear stress response, and other processes. Contraction mechanisms have been difficult to establish because stress fibers in cultured cells typically exert isometric tension and present little kinetic activity. In a recent study, living cell stress fibers were severed with laser nanoscissors and recoiled several mum over approximately 5 s. We developed a quantitative model of stress fibers based on known components and available structural information suggesting periodic sarcomeric organization similar to striated muscle. The model was applied to the severing assay and compared to the observed recoil. We conclude that the sarcomere force-length relation is similar to that of muscle with two distinct regions on the ascending limb and that substantial external drag forces act on the recoiling fiber corresponding to effective cytosolic viscosity approximately 10(4) times that of water. This may originate from both nonspecific and specific interactions. The model predicts highly nonuniform contraction with caps of collapsed sarcomeres growing at the severed ends. A directly measurable signature of external drag is that cap length and recoil distance increase at intermediate times as t(1/2). The severing data is consistent with this prediction.
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Affiliation(s)
- Matthew R Stachowiak
- Department of Chemical Engineering, Columbia University, New York, New York, USA
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31
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Jana SS, Kim KY, Mao J, Kawamoto S, Sellers JR, Adelstein RS. An alternatively spliced isoform of non-muscle myosin II-C is not regulated by myosin light chain phosphorylation. J Biol Chem 2009; 284:11563-71. [PMID: 19240025 DOI: 10.1074/jbc.m806574200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
We report a novel isoform of non-muscle myosin II-C (NM II-C), NM II-C2, that is generated by alternative splicing of an exon, C2, encoding 41 amino acids in mice (33 in humans). The 41 amino acids are inserted into loop 2 of the NM II-C heavy chain within the actin binding region. Unlike most vertebrate non-muscle and smooth muscle myosin IIs, baculovirus-expressed mouse heavy meromyosin (HMM) II-C2 demonstrates no requirement for regulatory myosin light chain (MLC(20)) phosphorylation for maximum actin-activated MgATPase activity or maximum in vitro motility as measured by the sliding actin filament assay. In contrast, noninserted HMM II-C0 and another alternatively spliced isoform HMM II-C1, which contains 8 amino acids inserted into loop 1, are dependent on MLC(20) phosphorylation for both actin-activated MgATPase activity and in vitro motility ( Kim, K. Y., Kovacs, M., Kawamoto, S., Sellers, J. R., and Adelstein, R. S. (2005) J. Biol. Chem. 280, 22769-22775 ). HMM II-C1C2, which contains both the C1 and C2 inserts, does not require MLC(20) phosphorylation for full activity similar to HMM II-C2. These constitutively active C2-inserted isoforms of NM II-C are expressed only in neuronal tissue. This is in contrast to NM II-C1 and NM II-C0, both of which are ubiquitously expressed. Full-length NM II-C2-GFP expressed in COS-7 cells localizes to filaments in interphase cells and to the cytokinetic ring in dividing cells.
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Affiliation(s)
- Siddhartha S Jana
- Laboratory of Molecular Cardiology and Laboratory of Molecular Physiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892, USA.
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32
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Kim KY, Kawamoto S, Bao J, Sellers JR, Adelstein RS. The B2 alternatively spliced isoform of nonmuscle myosin II-B lacks actin-activated MgATPase activity and in vitro motility. Biochem Biophys Res Commun 2007; 369:124-34. [PMID: 18060863 DOI: 10.1016/j.bbrc.2007.11.108] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2007] [Accepted: 11/15/2007] [Indexed: 10/24/2022]
Abstract
We report the initial biochemical characterization of an alternatively spliced isoform of nonmuscle heavy meromyosin (HMM) II-B2 and compare it with HMM II-B0, the nonspliced isoform. HMM II-B2 is the HMM derivative of an alternatively spliced isoform of endogenous nonmuscle myosin (NM) II-B, which has 21-amino acids inserted into loop 2, near the actin-binding region. NM II-B2 is expressed in the Purkinje cells of the cerebellum as well as in other neuronal cells [X. Ma, S. Kawamoto, J. Uribe, R.S. Adelstein, Function of the neuron-specific alternatively spliced isoforms of nonmuscle myosin II-B during mouse brain development, Mol. Biol. Cell 15 (2006) 2138-2149]. In contrast to any of the previously described isoforms of NM II (II-A, II-B0, II-B1, II-C0 and II-C1) or to smooth muscle myosin, the actin-activated MgATPase activity of HMM II-B2 is not significantly increased from a low, basal level by phosphorylation of the 20kDa myosin light chain (MLC-20). Moreover, although HMM II-B2 can bind to actin in the absence of ATP and is released in its presence, it cannot propel actin in the sliding actin filament assay following MLC-20 phosphorylation. Unlike HMM II-B2, the actin-activated MgATPase activity of a chimeric HMM with the 21-amino acid II-B2 sequence inserted into the homologous location in the heavy chain of HMM II-C is increased following MLC-20 phosphorylation. This indicates that the effect of the II-B2 insert is myosin heavy chain specific.
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Affiliation(s)
- Kye-Young Kim
- Laboratory of Molecular Cardiology, National Heart, Lung, and Blood Institute, National Institutes of Health Bethesda, MD 20892, USA
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33
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Kovács M, Thirumurugan K, Knight PJ, Sellers JR. Load-dependent mechanism of nonmuscle myosin 2. Proc Natl Acad Sci U S A 2007; 104:9994-9. [PMID: 17548820 PMCID: PMC1885822 DOI: 10.1073/pnas.0701181104] [Citation(s) in RCA: 155] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Loads on molecular motors regulate and coordinate their function. In a study that directly measures properties of internally strained myosin 2 heads bound to actin, we find that human nonmuscle myosins 2A and 2B show marked load-dependent changes in kinetics of ADP release but not in nucleotide binding. We show that the ADP release rate constant is increased 4-fold by the assisting load on one head and decreased 5-fold (for 2A) or 12-fold (for 2B) by the resisting load on the other. Thus these myosins, especially 2B, have marked mechanosensitivity of product release. By regulating the actin attachment of myosin heads, this provides a basis for energy-efficient tension maintenance without obstructing cellular contractility driven by other motors such as smooth muscle myosin. Whereas forward load accelerates the cycle of interaction with actin, resistive load increases duty ratio to favor tension maintenance by two-headed attachment.
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Affiliation(s)
- Mihály Kovács
- Laboratory of Molecular Physiology, National Heart, Lung, and Blood Institute/NIH, Bethesda, MD 20892-8015, USA.
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34
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Kempler K, Tóth J, Yamashita R, Mapel G, Robinson K, Cardasis H, Stevens S, Sellers JR, Battelle BA. Loop 2 of limulus myosin III is phosphorylated by protein kinase A and autophosphorylation. Biochemistry 2007; 46:4280-93. [PMID: 17367164 PMCID: PMC2580675 DOI: 10.1021/bi062112u] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Little is known about the functions of class III unconventional myosins although, with an N-terminal kinase domain, they are potentially both signaling and motor proteins. Limulus myosin III is particularly interesting because it is a phosphoprotein abundant in photoreceptors that becomes more heavily phosphorylated at night by protein kinase A. This enhanced nighttime phosphorylation occurs in response to signals from an endogenous circadian clock and correlates with dramatic changes in photoreceptor structure and function. We seek to understand the role of Limulus myosin III and its phosphorylation in photoreceptors. Here we determined the sites that become phosphorylated in Limulus myosin III and investigated its kinase, actin binding, and myosin ATPase activities. We show that Limulus myosin III exhibits kinase activity and that a major site for both protein kinase A and autophosphorylation is located within loop 2 of the myosin domain, an important actin binding region. We also identify the phosphorylation of an additional protein kinase A and autophosphorylation site near loop 2, and a predicted phosphorylation site within loop 2. We show that the kinase domain of Limulus myosin III shares some pharmacological properties with protein kinase A, and that it is a potential opsin kinase. Finally, we demonstrate that Limulus myosin III binds actin but lacks ATPase activity. We conclude that Limulus myosin III is an actin-binding and signaling protein and speculate that interactions between actin and Limulus myosin III are regulated by both second messenger mediated phosphorylation and autophosphorylation of its myosin domain within and near loop 2.
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Affiliation(s)
- Karen Kempler
- Whitney Laboratory for Marine Bioscience and the Department of Neuroscience, University of Florida, St. Augustine 32080
| | - Judit Tóth
- Department of Biochemistry, Eötvös Loránd University Pázmány P.s. 1/c. Budapest 1117, Hungary
- Laboratory of Molecular Physiology, NHLBI, National Institutes of Health, Bethesda, MD 20892-1762
| | - Roxanne Yamashita
- Laboratory of Molecular Physiology, NHLBI, National Institutes of Health, Bethesda, MD 20892-1762
| | - Gretchen Mapel
- Whitney Laboratory for Marine Bioscience and the Department of Neuroscience, University of Florida, St. Augustine 32080
| | - Kimberly Robinson
- Whitney Laboratory for Marine Bioscience and the Department of Neuroscience, University of Florida, St. Augustine 32080
| | - Helene Cardasis
- Proteomics Core of the ICBR, University of Florida, Gainesville 32010
- Department of Chemistry, University of Florida, Gainesville 32010
| | - Stanley Stevens
- Proteomics Core of the ICBR, University of Florida, Gainesville 32010
| | - James R. Sellers
- Laboratory of Molecular Physiology, NHLBI, National Institutes of Health, Bethesda, MD 20892-1762
| | - Barbara-Anne Battelle
- Whitney Laboratory for Marine Bioscience and the Department of Neuroscience, University of Florida, St. Augustine 32080
- CORRESPONDING AUTHOR: Barbara-Anne Battelle, Whitney Laboratory for Marine Bioscience, University of Florida, 9505 Ocean Shore Blvd. St. Augustine, FL 32080. Tel. 904-461-4022; Fax 904-461-008;
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35
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O'Connell CB, Tyska MJ, Mooseker MS. Myosin at work: motor adaptations for a variety of cellular functions. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2006; 1773:615-30. [PMID: 16904206 DOI: 10.1016/j.bbamcr.2006.06.012] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2006] [Revised: 05/22/2006] [Accepted: 06/30/2006] [Indexed: 12/30/2022]
Abstract
Cells have evolved multiple mechanisms to overcome the effects of entropy and diffusion to create a highly ordered environment. For cells to function properly, some components must be anchored to provide a framework or structure. Others must be rapidly transported over long distances to generate asymmetries in cell morphology and composition. To accomplish long-range transport, cells cannot rely on diffusion alone as many large organelles and macromolecular complexes are essentially immobilized by the dense meshwork of the cytosol. One strategy used by cells to overcome diffusion is to harness the free energy liberated by ATP hydrolysis through molecular motors. Myosins are a family of actin based molecular motors that have evolved a variety of ways to contribute to cellular organization through numerous modifications to the manner they convert that free energy into mechanical work.
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36
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Yang Y, Kovács M, Sakamoto T, Zhang F, Kiehart DP, Sellers JR. Dimerized Drosophila myosin VIIa: a processive motor. Proc Natl Acad Sci U S A 2006; 103:5746-51. [PMID: 16585515 PMCID: PMC1458644 DOI: 10.1073/pnas.0509935103] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The molecular mechanism of processive movement of single myosin molecules from classes V and VI along their actin tracks has recently attracted extraordinary attention. Another member of the myosin superfamily, myosin VII, plays vital roles in the sensory function of Drosophila and mammals. We studied the molecular mechanism of Drosophila myosin VIIa, using transient kinetics and single-molecule motility assays. Myosin VIIa moves along actin filaments as a processive, double-headed single molecule when dimerized by the inclusion of a leucine zipper at the C terminus of the coiled-coil domain. Its motility is approximately 8-10 times slower than that of myosin V, and its step size is 30 nm, which is consistent with the presence of five IQ motifs in its neck region. The kinetic basis for the processive motility of myosin VIIa is the relative magnitude of the release rate constants of phosphate (fast) and ADP (slow) as in myosins V and VI. The ATPase pathway is rate-limited by a reversible interconversion between two distinct ADP-bound actomyosin states, which results in high steady-state occupancy of a strongly actin-bound myosin species. The distinctive features of myosin VIIa (long run lengths, slow motility) will be very useful in video-based single-molecule applications. In cells, this kinetic behavior would allow myosin VIIa to exert and hold tension on actin filaments and, if dimerized, to function as a processive cargo transporter.
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Affiliation(s)
- Yi Yang
- *Laboratory of Molecular Physiology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-1762
| | - Mihály Kovács
- *Laboratory of Molecular Physiology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-1762
- Department of Biochemistry, Eötvös University, H-1117 Budapest, Pázmány P. sétány 1/C, Hungary; and
| | - Takeshi Sakamoto
- *Laboratory of Molecular Physiology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-1762
| | - Fang Zhang
- *Laboratory of Molecular Physiology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-1762
| | - Daniel P. Kiehart
- Developmental, Cell, and Molecular Biology Group, Department of Biology, Duke University, Durham, NC 27708-1000
| | - James R. Sellers
- *Laboratory of Molecular Physiology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-1762
- To whom correspondence should be addressed. E-mail:
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37
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Yang Y, Kovács M, Xu Q, Anderson JB, Sellers JR. Myosin VIIB from Drosophila is a high duty ratio motor. J Biol Chem 2005; 280:32061-8. [PMID: 16055438 DOI: 10.1074/jbc.m506765200] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Myosin VII is an unconventional myosin widely expressed in organisms ranging from amoebae to mammals that has been shown to play vital roles in cell adhesion and phagocytosis. Here we present the first study of the mechanism of action of a myosin VII isoform. We have expressed a truncated single-headed Drosophila myosin VIIB construct in the baculovirus-Sf9 system that bound calmodulin light chains. By using steady-state and transient kinetic methods, we showed that myosin VIIB exhibits a fast release of phosphate and a slower, rate-limiting ADP release from actomyosin. As a result, myosin VIIB will be predominantly strongly bound to actin during steady-state ATP hydrolysis (its duty ratio will be at least 80%). This kinetic pattern is in many respects similar to that of the single-molecule vesicle transporters myosin V and VI. The enzymatic properties of myosin VIIB provide a kinetic basis for processivity upon possible dimerization via the C-terminal domains of the heavy chain. Our experiments also revealed conformational heterogeneity of the actomyosin VIIB complex in the absence of nucleotide.
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Affiliation(s)
- Yi Yang
- Laboratory of Molecular Physiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892-1762, USA
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38
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Liu X, Shu S, Kovács M, Korn ED. Biological, biochemical, and kinetic effects of mutations of the cardiomyopathy loop of Dictyostelium myosin II: importance of ALA400. J Biol Chem 2005; 280:26974-83. [PMID: 15897189 PMCID: PMC1201472 DOI: 10.1074/jbc.m504453200] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cardiomyopathy (CM)-loop of the heavy chain of class-II myosins begins with a highly conserved Arg residue (whose mutation in human beta-cardiac myosin II results in familial hypertrophic cardiomyopathy). The CM-loop of Dictyostelium myosin II (Arg397-Gln407) is essential for its biological functions and biochemical activities. We found that the CM-loop of smooth muscle myosin II substituted partially, and the CM-loop of beta-cardiac myosin II less well, for growth, capping of surface receptors and development, and the actin-activated MgATPase and in vitro motility activities of purified myosins. There was little correlation between the biochemical and biological activities of the two chimeras and 19 point mutants, but only the five mutants with k cat/K actin values equivalent to wild-type myosin supported essentially full biological function. The three point mutations of Arg397 equivalent to those that result in hypertrophic cardiomyopathy in humans had minimal biological effects and different biochemical effects. The A400V mutation rendered full-length wild-type myosin almost completely inactive, both in vitro and in vivo, and the reverse V400A mutation in the cardiac CM-loop chimera restored almost full activity, even though the sequence still differed from wild-type in 7 of 11 positions. Transient kinetic studies of acto-subfragment-1 (S1) showed that the chimeras and the Ala/Val, Val/Ala mutations do not affect the equilibrium or the association and dissociation rate constants for either ATP or ADP binding to acto-S1 or the rate of ATP-induced dissociation of acto-S1. We conclude that the Ala/Val, Val/Ala mutations affect the release of Pi from acto-S1.ADP.Pi. In addition, Val at position 400 substantially reduces the affinity of actin for S1 in the absence of nucleotide.
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Affiliation(s)
- Xiong Liu
- Laboratory of Cell Biology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892, USA
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39
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Kim KY, Kovács M, Kawamoto S, Sellers JR, Adelstein RS. Disease-associated mutations and alternative splicing alter the enzymatic and motile activity of nonmuscle myosins II-B and II-C. J Biol Chem 2005; 280:22769-75. [PMID: 15845534 DOI: 10.1074/jbc.m503488200] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Human families with single amino acid mutations in nonmuscle myosin heavy chain (NMHC) II-A (MYH9) and II-C (MYH14) have been described as have mice generated with a point mutation in NMHC II-B (MYH10). These mutations (R702C and N93K in human NMHC II-A, R709C in murine NMHC II-B, and R726S in human NMHC II-C) result in phenotypes affecting kidneys, platelets, and leukocytes (II-A), heart and brain (II-B), and the inner ear (II-C). To better understand the mechanisms underlying these defects, we characterized the in vitro activity of mutated and wild-type baculovirus-expressed heavy meromyosin (HMM) II-B and II-C. We also expressed two alternatively spliced isoforms of NMHC II-C which differ by inclusion/exclusion of eight amino acids in loop 1, with and without mutations. Comparison of the actin-activated MgATPase activity and in vitro motility shows that mutation of residues Asn-97 and Arg-709 in HMM II-B and the homologous residue Arg-722 (Arg-730 in the alternatively spliced isoform) in HMM II-C decreases both parameters but affects in vitro motility more severely. Analysis of the transient kinetics of the HMM II-B R709C mutant shows an extremely tight affinity of HMM for ADP and a very slow release of ADP from acto-HMM. Although mutations generally decreased HMM activity, the R730S mutation in HMM II-C, unlike the R730C mutation, had no effect on actin-activated MgATPase activity but decreased the rate of in vitro motility by 75% compared with wild type. Insertion of eight amino acids into the HMM II-C heavy chain increases both actin-activated MgATPase activity and in vitro motility.
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Affiliation(s)
- Kye-Young Kim
- Laboratory of Molecular Cardiology and Laboratory of Molecular Physiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892, USA
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40
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Abstract
We have performed a detailed biochemical kinetic and spectroscopic study on a recombinant myosin X head construct to establish a quantitative model of the enzymatic mechanism of this membrane-bound myosin. Our model shows that during steady-state ATP hydrolysis, myosin X exhibits a duty ratio (i.e. the fraction of the cycle time spent strongly bound to actin) of around 16%, but most of the remaining myosin heads are also actin-attached even at moderate actin concentrations in the so-called "weak" actin-binding states. Contrary to the high duty ratio motors myosin V and VI, the ADP release rate constant from actomyosin X is around five times greater than the maximal steady-state ATPase activity, and the kinetic partitioning between different weak actin-binding states is a major contributor to the rate limitation of the enzymatic cycle. Two different ADP states of myosin X are populated in the absence of actin, one of which shows very similar kinetic properties to actomyosin.ADP. The nucleotide-free complex of myosin X with actin shows unique spectral and biochemical characteristics, indicating a special mode of actomyosin interaction.
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41
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Sellers JR, Wang F, Chantler PD. Trifluoperazine inhibits the MgATPase activity and in vitro motility of conventional and unconventional myosins. J Muscle Res Cell Motil 2004; 24:579-85. [PMID: 14870973 DOI: 10.1023/b:jure.0000009969.04562.58] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Trifluoperazine, a calmodulin antagonist, has recently been shown to inhibit the MgATPase activity of scallop myosin in the absence of light chain dissociation (Patel et al. (2000) J Biol Chem 275: 4880-4888). To investigate the generality of this observation and the mechanism by which it occurs, we have examined the ability of trifluoperazine to inhibit the enzymatic properties of other conventional and unconventional myosins. We show that trifluoperazine can inhibit the actin-activated MgATPase activity of rabbit skeletal muscle myosin II heavy meromyosin (HMM), phosphorylated turkey gizzard smooth muscle myosin II HMM, phosphorylated human nonmuscle myosin IIA HMM and myosin V subfragment-1 (S1). In all cases half maximal inhibition occurred at 50-75 microM trifluoperazine while light chains (myosin II) or calmodulin (myosin V) remained associated with the heavy chains. In vitro motility of all myosins tested was completely inhibited by trifluoperazine. Chymotryptic digestion of baculovirus-expressed myosin V HMM possessing only two calmodulin binding sites yielded a minimal motor fragment with no bound calmodulin. The MgATPase of this fragment was inhibited by trifluoperazine over the same range of concentrations as the S1 fragment of myosin.
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Affiliation(s)
- James R Sellers
- Laboratory of Molecular Cardiology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA
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42
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Straight AF, Field CM, Mitchison TJ. Anillin binds nonmuscle myosin II and regulates the contractile ring. Mol Biol Cell 2004; 16:193-201. [PMID: 15496454 PMCID: PMC539163 DOI: 10.1091/mbc.e04-08-0758] [Citation(s) in RCA: 212] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
We demonstrate that the contractile ring protein anillin interacts directly with nonmuscle myosin II and that this interaction is regulated by myosin light chain phosphorylation. We show that despite their interaction, anillin and myosin II are independently targeted to the contractile ring. Depletion of anillin in Drosophila or human cultured cells results in cytokinesis failure. Human cells depleted for anillin fail to properly regulate contraction by myosin II late in cytokinesis and fail in abscission. We propose a role for anillin in spatially regulating the contractile activity of myosin II during cytokinesis.
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Affiliation(s)
- Aaron F Straight
- Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305, USA.
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43
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Golomb E, Ma X, Jana SS, Preston YA, Kawamoto S, Shoham NG, Goldin E, Conti MA, Sellers JR, Adelstein RS. Identification and characterization of nonmuscle myosin II-C, a new member of the myosin II family. J Biol Chem 2003; 279:2800-8. [PMID: 14594953 DOI: 10.1074/jbc.m309981200] [Citation(s) in RCA: 256] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A previously unrecognized nonmuscle myosin II heavy chain (NMHC II), which constitutes a distinct branch of the nonmuscle/smooth muscle myosin II family, has recently been revealed in genome data bases. We characterized the biochemical properties and expression patterns of this myosin. Using nucleotide probes and affinity-purified antibodies, we found that the distribution of NMHC II-C mRNA and protein (MYH14) is widespread in human and mouse organs but is quantitatively and qualitatively distinct from NMHC II-A and II-B. In contrast to NMHC II-A and II-B, the mRNA level in human fetal tissues is substantially lower than in adult tissues. Immunofluorescence microscopy showed distinct patterns of expression for all three NMHC isoforms. NMHC II-C contains an alternatively spliced exon of 24 nucleotides in loop I at a location analogous to where a spliced exon appears in NMHC II-B and in the smooth muscle myosin heavy chain. However, unlike neuron-specific expression of the NMHC II-B insert, the NMHC II-C inserted isoform has widespread tissue distribution. Baculovirus expression of noninserted and inserted NMHC II-C heavy meromyosin (HMM II-C/HMM II-C1) resulted in significant quantities of expressed protein (mg of protein) for HMM II-C1 but not for HMM II-C. Functional characterization of HMM II-C1 by actin-activated MgATPase activity demonstrated a V(max) of 0.55 + 0.18 s(-1), which was half-maximally activated at an actin concentration of 16.5 + 7.2 microm. HMM II-C1 translocated actin filaments at a rate of 0.05 + 0.011 microm/s in the absence of tropomyosin and at 0.072 + 0.019 microm/s in the presence of tropomyosin in an in vitro motility assay.
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Affiliation(s)
- Eliahu Golomb
- Laboratory of Molecular Cardiology, NHLBI, National Institute of Health, Bethesda, Maryland 20892, USA.
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44
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Kovács M, Wang F, Hu A, Zhang Y, Sellers JR. Functional divergence of human cytoplasmic myosin II: kinetic characterization of the non-muscle IIA isoform. J Biol Chem 2003; 278:38132-40. [PMID: 12847096 DOI: 10.1074/jbc.m305453200] [Citation(s) in RCA: 179] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cytoplasmic (or non-muscle) myosin II isoforms are widely expressed molecular motors playing essential cellular roles in cytokinesis and cortical tension maintenance. Two of the three human non-muscle myosin II isoforms (IIA and IIB) have been investigated at the protein level. Transient kinetics of non-muscle myosin IIB showed that this motor has a very high actomyosin ADP affinity and slow ADP release. Here we report the kinetic characterization of the non-muscle myosin IIA isoform. Similar to non-muscle myosin IIB, non-muscle myosin IIA shows high ADP affinity and little enhancement of the ADP release rate by actin. The ADP release rate constant, however, is more than an order of magnitude higher than the steady-state ATPase rate. This implies that non-muscle myosin IIA spends only a small fraction of its ATPase cycle time in strongly actin-bound states, which is in contrast to non-muscle myosin IIB. Non-muscle myosin II isoforms thus appear to have distinct enzymatic properties that may be of importance in carrying out their cellular functions.
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Affiliation(s)
- Mihály Kovács
- Laboratory of Molecular Cardiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892-1762, USA
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Wang F, Kovacs M, Hu A, Limouze J, Harvey EV, Sellers JR. Kinetic mechanism of non-muscle myosin IIB: functional adaptations for tension generation and maintenance. J Biol Chem 2003; 278:27439-48. [PMID: 12704189 DOI: 10.1074/jbc.m302510200] [Citation(s) in RCA: 190] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Besides driving contraction of various types of muscle tissue, conventional (class II) myosins serve essential cellular functions and are ubiquitously expressed in eukaryotic cells. Three different isoforms in the human myosin complement have been identified as non-muscle class II myosins. Here we report the kinetic characterization of a human non-muscle myosin IIB subfragment-1 construct produced in the baculovirus expression system. Transient kinetic data show that most steps of the actomyosin ATPase cycle are slowed down compared with other class II myosins. The ADP affinity of subfragment-1 is unusually high even in the presence of actin filaments, and the rate of ADP release is close to the steady-state ATPase rate. Thus, non-muscle myosin IIB subfragment-1 spends a significantly higher proportion of its kinetic cycle strongly attached to actin than do the muscle myosins. This feature is even more pronounced at slightly elevated ADP levels, and it may be important in carrying out the cellular functions of this isoform working in small filamentous assemblies.
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Affiliation(s)
- Fei Wang
- Laboratory of Molecular Cardiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892-1762, USA
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46
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Linz-McGillem LA, Alliegro MC. Myosin II in retinal pigmented epithelial cells: evidence for an association with membranous vesicles. Exp Eye Res 2003; 76:543-52. [PMID: 12697418 DOI: 10.1016/s0014-4835(03)00031-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The goal of this study was to further characterize and identify possible functions for a cytoplasmic myosin II protein which we have isolated from retinal pigmented epithelial (RPE) cells. The nucleotide and deduced amino acid sequences are highly identical to non-muscle myosin heavy chain II-A (NMMHC II-A). However, this RPE myosin displays characteristics that are atypical of other myosins, including an affinity for carbohydrate and a C-terminal sequence extension, suggesting it may have a specialized function. In this study, reverse transcriptase-PCR using isoform-specific primers demonstrated that the RPE myosin and conventional NMMHC II-A have overlapping but distinguishable tissue expression profiles. To gain clues to function, subcellular distribution was determined in motile RPE cells using indirect immunofluorescence. In addition to subtle differences in localization that appeared to further distinguish this molecule from NMMHC II-A, these studies revealed a colocalization with phagocytosed intracellular vesicles. In vitro experiments suggest that the association in situ was not simply coincidental, because isolated vesicles interacted with the protein in cosedimentation assays. Taken together, our observations suggest the RPE myosin exhibits characteristics different from conventional myosin II-A and may function in intracellular vesicle transport.
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Affiliation(s)
- Laura A Linz-McGillem
- Department of Cell Biology and Anatomy, Louisiana State University Health Sciences Center, New Orleans, LA, USA. llinzmc
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47
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Hu A, Wang F, Sellers JR. Mutations in human nonmuscle myosin IIA found in patients with May-Hegglin anomaly and Fechtner syndrome result in impaired enzymatic function. J Biol Chem 2002; 277:46512-7. [PMID: 12237319 DOI: 10.1074/jbc.m208506200] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A family of autosomal-dominant diseases including May-Hegglin anomaly, Fechtner syndrome, Sebastian syndrome, Alport syndrome, and Epstein syndrome are commonly characterized by giant platelets and thrombocytopenia. In addition, there may be leukocyte inclusions, deafness, cataracts, and nephritis, depending on the syndrome. Mutations in the human nonmuscle myosin IIA heavy chain gene (MYH9) have been linked to these diseases. Two of the recently described mutations, N93K and R702C, are conserved in smooth and nonmuscle myosins from vertebrates and lie in the head domain of myosin. Interestingly, the two mutations lie within close proximity in the three-dimensional structure of myosin. These two mutations were engineered into a heavy meromyosin-like recombinant fragment of nonmuscle myosin IIA, which was expressed in baculovirus along with the appropriate light chains. The R702C mutant displays 25% of the maximal MgATPase activity of wild type heavy meromyosin and moves actin filaments at half the wild type rate. The effects of the N93K mutation are more dramatic. This heavy meromyosin has only 4% of the maximal MgATPase activity of wild type and does not translocate actin filaments in an in vitro motility assay. Biochemical characterization of the mutant is consistent with this mutant being unable to fully adopt the "on" conformation.
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Affiliation(s)
- Aihua Hu
- Laboratory of Molecular Cardiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892-1762, USA
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48
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Cremo CR, Wang F, Facemyer K, Sellers JR. Phosphorylation-dependent regulation is absent in a nonmuscle heavy meromyosin construct with one complete head and one head lacking the motor domain. J Biol Chem 2001; 276:41465-72. [PMID: 11517231 DOI: 10.1074/jbc.m107103200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To understand the domain requirements of phosphorylation-dependent regulation, we prepared three recombinant constructs of nonmuscle heavy meromyosin IIB containing 1) two complete heads, 2) one complete head and one head lacking the motor domain, and 3) one complete head and one head lacking both motor and regulatory domains. Steady-state ATPase measurements showed that phosphorylation did not alter the affinity for actin by more than a factor of 2 for any construct. Phosphorylation increased V(max) by a factor of 10 for construct 1 and 1.5-3 for construct 2 but had no effect for construct 3. Single turnover measurements, a better measure of slow rates inherent to unphosphorylated regulated myosins, showed that the single-headed construct 2, like construct 3 retains less than 1% of the regulatory properties of the double-headed construct 1 (300-fold activation). Therefore, a complete head cannot be down-regulated by a regulatory domain (without the motor domain) on the partner head. Two motor domains are required for regulation. This result is predicted by a structural model (Wendt, T., Taylor, D., Messier, T., Trybus, K. M., and Taylor, K. A. (1999) J. Cell Biol. 147, 1385-1390) showing interaction between the motor domains for unphosphorylated smooth muscle myosin, if motor-motor interaction is the basis for down-regulation.
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Affiliation(s)
- C R Cremo
- Department of Biochemistry, The University of Nevada, Reno, Nevada 89557, USA
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Liu X, Osherov N, Yamashita R, Brzeska H, Korn ED, May GS. Myosin I mutants with only 1% of wild-type actin-activated MgATPase activity retain essential in vivo function(s). Proc Natl Acad Sci U S A 2001; 98:9122-7. [PMID: 11459943 PMCID: PMC55383 DOI: 10.1073/pnas.161285698] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/07/2001] [Indexed: 11/18/2022] Open
Abstract
The single class I myosin (MYOA) of Aspergillus nidulans is essential for hyphal growth. It is generally assumed that the functions of all myosins depend on their actin-activated MgATPase activity. Here we show that MYOA mutants with no more than 1% of the actin-activated MgATPase activity of wild-type MYOA in vitro and no detectable in vitro motility activity can support fungal cell growth, albeit with a delay in germination time and a reduction in hyphal elongation. From these and other data, we conclude that the essential role(s) of myosin I in A. nidulans is probably structural, requiring little, if any, actin-activated MgATPase or motor activity, which have long been considered the defining characteristics of the myosin family.
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Affiliation(s)
- X Liu
- Laboratory of Cell Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Building 50, Room 2517, Bethesda, MD 20892, USA
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50
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Abstract
High-resolution structures of the motor domain of myosin II and lower resolution actin-myosin structures have led to the "swinging lever arm" model for myosin force generation. The available kinetic data are not all easily reconciled with this model and understanding the final details of the myosin motor mechanism must await actin-myosin co-crystals. The observation that myosin can populate multiple states in the absence of actin has nonetheless led to significant insights. The currently known myosin structures correspond to defined kinetic states that bind weakly (K(d)>microM) to actin. It is possible that the myosin lever arm could complete its swing before strong binding to actin and force generation--a process that would correspond, in the absence of load, to a Brownian ratchet. We further suggest that, under load, internal springs within the myosin head could decouple force generation and lever arm movement.
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Affiliation(s)
- A Houdusse
- Structural Motility, Institut Curie CNRS, UMR 144, 26 rue d'Ulm, 75248 05 Paris Cedex, France.
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