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Mamelona J, Filice L, Oussedik Y, Crapoulet N, Ouellette RJ, Marrero A. A novel missense mutation in the MYH7 gene causes an uncharacteristic phenotype of myosin storage myopathy: a case report. BMC MEDICAL GENETICS 2019; 20:78. [PMID: 31068177 PMCID: PMC6507130 DOI: 10.1186/s12881-019-0804-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Accepted: 04/09/2019] [Indexed: 11/10/2022]
Abstract
BACKGROUND Few manuscripts have reported phenotypes of skeletal muscle myopathies caused by mutations in the head region of slow/cardiac beta-myosin heavy chain (MyHCI). Among the patients, some of them showed the phenotype of skeletal muscle weakness with the obvious clinical features of cardiomyopathy while others showed pure skeletal muscle weakness with no symptoms of cardiac involvement. Genotype-phenotype relationship regarding the effect of a mutation on MyHCI is complex. Questions regarding why some mutations cause cardiomyopathy or skeletal muscle disorders alone or a combination of both still need to be answered. More findings in genetic variation are needed to extend knowledge of mutations in the MYH7 gene linked to skeletal muscle disorders. CASE PRESENTATION Here we present a female adult patient with a phenotype of childhood onset of muscular disorders and predominant involvement of thigh muscles with biopsy showing intrasarcoplasmic inclusion bodies. Whole exome sequencing showed that variant c.1370 T > G (p.Ile457Arg) in the MYH7 gene is a missense mutation possibly linked to the clinical findings. Our patient likely shows an uncharacteristic myosin storage myopathy associated with respiratory and cardiac involvement linked to a missense mutation in the head of MyHCI. CONCLUSIONS Given this mutation is located within the motor domain of MyHCI, this might affect the regulation of myosin mechano-chemical activity during the contractile cycle. Consequently, this potentially damaging effect can be easily amplified within the network of ~ 300-myosin molecules forming the thick filament and therefore become cumulatively deleterious, affecting, in turn, the overall organization and performance of sarcomere.
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Affiliation(s)
- Jean Mamelona
- Department of Neurology, Dr.-Georges-L.-Dumont University Hospital Center, 330 University Avenue, Moncton, NB, E1C 2Z3, Canada
| | - Louisa Filice
- Centre de Formation Médicale du Nouveau-Brunswick, 100 Des Aboiteaux Street, Moncton, NB, E1A 7R1, Canada
| | - Youcef Oussedik
- Department of Pathology, Dr.-Georges-L.-Dumont University Hospital Center, 330 University Avenue, Moncton, NB, E1C 2Z3, Canada
| | - Nicolas Crapoulet
- Molecular Genetics, Dr.-Alfred-Bastarche Laboratory, 37 Providence Street, Moncton, NB, E1C 8X3, Canada
| | - Rodney J Ouellette
- Molecular Genetics, Dr.-Alfred-Bastarche Laboratory, 37 Providence Street, Moncton, NB, E1C 8X3, Canada
| | - Alier Marrero
- Department of Neurology, Dr.-Georges-L.-Dumont University Hospital Center, 330 University Avenue, Moncton, NB, E1C 2Z3, Canada. .,Centre de Formation Médicale du Nouveau-Brunswick, 100 Des Aboiteaux Street, Moncton, NB, E1A 7R1, Canada.
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2
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The structure of the catalytic domain of the ATP synthase from Mycobacterium smegmatis is a target for developing antitubercular drugs. Proc Natl Acad Sci U S A 2019; 116:4206-4211. [PMID: 30683723 DOI: 10.1073/pnas.1817615116] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The crystal structure of the F1-catalytic domain of the adenosine triphosphate (ATP) synthase has been determined from Mycobacterium smegmatis which hydrolyzes ATP very poorly. The structure of the α3β3-component of the catalytic domain is similar to those in active F1-ATPases in Escherichia coli and Geobacillus stearothermophilus However, its ε-subunit differs from those in these two active bacterial F1-ATPases as an ATP molecule is not bound to the two α-helices forming its C-terminal domain, probably because they are shorter than those in active enzymes and they lack an amino acid that contributes to the ATP binding site in active enzymes. In E. coli and G. stearothermophilus, the α-helices adopt an "up" state where the α-helices enter the α3β3-domain and prevent the rotor from turning. The mycobacterial F1-ATPase is most similar to the F1-ATPase from Caldalkalibacillus thermarum, which also hydrolyzes ATP poorly. The βE-subunits in both enzymes are in the usual "open" conformation but appear to be occupied uniquely by the combination of an adenosine 5'-diphosphate molecule with no magnesium ion plus phosphate. This occupation is consistent with the finding that their rotors have been arrested at the same point in their rotary catalytic cycles. These bound hydrolytic products are probably the basis of the inhibition of ATP hydrolysis. It can be envisaged that specific as yet unidentified small molecules might bind to the F1 domain in Mycobacterium tuberculosis, prevent ATP synthesis, and inhibit the growth of the pathogen.
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Vandenboom R. Modulation of Skeletal Muscle Contraction by Myosin Phosphorylation. Compr Physiol 2016; 7:171-212. [PMID: 28135003 DOI: 10.1002/cphy.c150044] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The striated muscle sarcomere is a highly organized and complex enzymatic and structural organelle. Evolutionary pressures have played a vital role in determining the structure-function relationship of each protein within the sarcomere. A key part of this multimeric assembly is the light chain-binding domain (LCBD) of the myosin II motor molecule. This elongated "beam" functions as a biological lever, amplifying small interdomain movements within the myosin head into piconewton forces and nanometer displacements against the thin filament during the cross-bridge cycle. The LCBD contains two subunits known as the essential and regulatory myosin light chains (ELC and RLC, respectively). Isoformic differences in these respective species provide molecular diversity and, in addition, sites for phosphorylation of serine residues, a highly conserved feature of striated muscle systems. Work on permeabilized skeletal fibers and thick filament systems shows that the skeletal myosin light chain kinase catalyzed phosphorylation of the RLC alters the "interacting head motif" of myosin motor heads on the thick filament surface, with myriad consequences for muscle biology. At rest, structure-function changes may upregulate actomyosin ATPase activity of phosphorylated cross-bridges. During activation, these same changes may increase the Ca2+ sensitivity of force development to enhance force, work, and power output, outcomes known as "potentiation." Thus, although other mechanisms may contribute, RLC phosphorylation may represent a form of thick filament activation that provides a "molecular memory" of contraction. The clinical significance of these RLC phosphorylation mediated alterations to contractile performance of various striated muscle systems are just beginning to be understood. © 2017 American Physiological Society. Compr Physiol 7:171-212, 2017.
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Affiliation(s)
- Rene Vandenboom
- Department of Kinesiology, Faculty of Applied Health Sciences, Brock University, Ontario, Canada
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Kim SJ, Lee S, Park HJ, Kang TH, Sagong B, Baek JI, Oh SK, Choi JY, Lee KY, Kim UK. Genetic association of MYH genes with hereditary hearing loss in Korea. Gene 2016; 591:177-182. [DOI: 10.1016/j.gene.2016.07.011] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Revised: 06/15/2016] [Accepted: 07/04/2016] [Indexed: 01/12/2023]
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5
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Chantler PD. Scallop Adductor Muscles. ACTA ACUST UNITED AC 2016. [DOI: 10.1016/b978-0-444-62710-0.00004-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/07/2023]
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6
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How release of phosphate from mammalian F1-ATPase generates a rotary substep. Proc Natl Acad Sci U S A 2015; 112:6009-14. [PMID: 25918412 PMCID: PMC4434703 DOI: 10.1073/pnas.1506465112] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
ATP, the fuel of life, is produced in the mitochondria of living cells by a molecular machine consisting of two motors linked by a rotor. One motor generates rotation by consuming energy derived from sugars and fats in foodstuffs; the other uses energy transmitted by the rotor to synthesize ATP molecules from their building blocks, ADP and phosphate. The synthetic motor can be uncoupled from the machine, and its rotary action can be studied by driving the motor backward with energy from ATP, releasing ADP and phosphate in the process. Each cycle has three 120° steps, each made of substeps of 65°, 25°, and 30° in humans. We have explained how release of phosphate from the machine generates the 25° rotary substep. The rotation of the central stalk of F1-ATPase is driven by energy derived from the sequential binding of an ATP molecule to its three catalytic sites and the release of the products of hydrolysis. In human F1-ATPase, each 360° rotation consists of three 120° steps composed of substeps of about 65°, 25°, and 30°, with intervening ATP binding, phosphate release, and catalytic dwells, respectively. The F1-ATPase inhibitor protein, IF1, halts the rotary cycle at the catalytic dwell. The human and bovine enzymes are essentially identical, and the structure of bovine F1-ATPase inhibited by IF1 represents the catalytic dwell state. Another structure, described here, of bovine F1-ATPase inhibited by an ATP analog and the phosphate analog, thiophosphate, represents the phosphate binding dwell. Thiophosphate is bound to a site in the αEβE-catalytic interface, whereas in F1-ATPase inhibited with IF1, the equivalent site is changed subtly and the enzyme is incapable of binding thiophosphate. These two structures provide a molecular mechanism of how phosphate release generates a rotary substep as follows. In the active enzyme, phosphate release from the βE-subunit is accompanied by a rearrangement of the structure of its binding site that prevents released phosphate from rebinding. The associated extrusion of a loop in the βE-subunit disrupts interactions in the αEβE-catalytic interface and opens it to its fullest extent. Other rearrangements disrupt interactions between the γ-subunit and the C-terminal domain of the αE-subunit. To restore most of these interactions, and to make compensatory new ones, the γ-subunit rotates through 25°–30°.
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Chapter 4 Scallop adductor muscles: Structure and function. SCALLOPS: BIOLOGY, ECOLOGY AND AQUACULTURE 2006. [DOI: 10.1016/s0167-9309(06)80031-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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8
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Lan G, Sun SX. Dynamics of myosin-driven skeletal muscle contraction: I. Steady-state force generation. Biophys J 2005; 88:4107-17. [PMID: 15778440 PMCID: PMC1305641 DOI: 10.1529/biophysj.104.056846] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Skeletal muscle contraction is a canonical example of motor-driven force generation. Despite the long history of research in this topic, a mechanistic explanation of the collective myosin force generation is lacking. We present a theoretical model of muscle contraction based on the conformational movements of individual myosins and experimentally measured chemical rate constants. Detailed mechanics of the myosin motor and the geometry of the sarcomere are taken into account. Two possible scenarios of force generation are examined. We find only one of the scenarios can give rise to a plausible contraction mechanism. We propose that the synchrony in muscle contraction is due to a force-dependent ADP release step. Computational results of a half sarcomere with 150 myosin heads can explain the experimentally measured force-velocity relationship and efficiency data. We predict that the number of working myosin motors increases as the load force is increased, thus showing synchrony among myosin motors during muscle contraction. We also find that titin molecules anchoring the thick filament are passive force generators in assisting muscle contraction.
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Affiliation(s)
- Ganhui Lan
- Department of Mechanical Engineering, Johns Hopkins University, Baltimore, Maryland, USA
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9
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Abstract
The basis for all biological movement is the conversion of chemical energy to mechanical energy by different classes of motor proteins. In skeletal muscle this motor protein is myosin II, a thick filament-based molecule that harnesses the free energy furnished by ATP hydrolysis to perform mechanical work against actin proteins of the thin filament. The cyclic attachment and detachment of myosin with actin that generates muscle force and shortening is Ca2+ regulated. Intense muscle activity may lead to metabolically induced inhibitions to the function of these myofibrillar proteins when Ca2+ regulation is normal, a phenomenon referred to as myofibrillar fatigue. Studies using single muscle fibers at room temperature or lower have shown that myosin motor function is inhibited by the accumulation of the ATP-hydrolysis products ADP, Pi, and H+ as well as by excess generation of reactive oxygen species (ROS). These metabolically induced impairments to myosin motor function reduce muscle work and power output by impairing maximal Ca2+ activated force, the Ca2+ sensitivity of force, and/or unloaded shortening velocity. Based on uncertainties about their inhibitory effect on muscle function at more physiological temperatures, the influence of ATP-hydrolysis product and ROS accumulation on myofibrillar protein function of human skeletal muscle remains to be clarified. Key words: actin, myosin, muscle contraction
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Affiliation(s)
- Rene Vandenboom
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, 48190, USA
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10
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Abstract
MECs are distributed on the basal aspect of the intercalated duct and acinus of human and rat salivary glands. However, they do not occur in the acinus of rat parotid glands, and sometimes occur in the striated duct of human salivary glands. MECs, as the name implies, have structural features of both epithelial and smooth muscle cells. They contract by autonomic nervous stimulation, and are thought to assist the secretion by compressing and/or reinforcing the underlying parenchyma. MECs can be best observed by immunocytochemistry. There are three types of immunocytochemical markers of MECs in salivary glands. The first type includes smooth muscle protein markers such as alpha-SMA, SMMHC, h-caldesmon and basic calponin, and these are expressed by MECs and the mesenchymal vasculature. The second type is expressed by MECs and the duct cells and includes keratins 14, 5 and 17, alpha 1 beta 1 integrin, and metallothionein. Vimentin is the third type and, in addition to MECs, is expressed by the mesenchymal cells and some duct cells. The same three types of markers are used for studying the developing gland. Development of MECs starts after the establishment of an extensively branched system of cellular cords each of which terminates as a spherical cell mass, a terminal bud. The pluripotent stem cell generates the acinar progenitor in the terminal bud and the ductal progenitor in the cellular cord. The acinar progenitor differentiates into MECs, acinar cells and intercalated duct cells, whereas the ductal progenitor differentiates into the striated and excretory duct cells. Both in the terminal bud and in the cellular cord, the immediate precursors of all types of the epithelial cells appear to express vimentin. The first identifiable MECs are seen at the periphery of the terminal bud or the immature acinus (the direct progeny of the terminal bud) as somewhat flattened cells with a single cilium projecting toward them. They express vimentin and later alpha-SMA and basic calponin. At the next developmental stage, MECs acquire cytoplasmic microfilaments and plasmalemmal caveolae but not as much as in the mature cell. They express SMMHC and, inconsistently, K14. This protein is consistently expressed in the mature cell. K14 is expressed by duct cells, and vimentin is expressed by both mesenchymal and epithelial cells. After development, the acinar progenitor and the ductal progenitor appear to reside in the acinus/intercalated duct and the larger ducts, respectively, and to contribute to the tissue homeostasis. Under unusual conditions such as massive parenchymal destruction, the acinar progenitor contributes to the maintenance of the larger ducts that result in the occurrence of striated ducts with MECs. The acinar progenitor is the origin of salivary gland tumors containing MECs. MECs in salivary gland tumors are best identified by immunocytochemistry for alpha-SMA. There are significant numbers of cells related to luminal tumor cells in the non-luminal tumor cells that have been believed to be neoplastic MECs.
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Affiliation(s)
- Yuzo Ogawa
- Department of Oral Pathology, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan.
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11
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Walker JW. Kinetics of the Actin–Myosin Interaction. Compr Physiol 2002. [DOI: 10.1002/cphy.cp020106] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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12
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Abstract
This review focuses on selected papers that illustrate an historical perspective and the current knowledge of myosin structure and function in protists. The review contains a general description of myosin structure, a phylogenetic tree of the myosin classes, and descriptions of myosin isoforms identified in protists. Each myosin is discussed within the context of the taxonomic group of the organism in which the myosin has been identified. Domain structure, cellular location, function, and regulation are described for each myosin.
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Affiliation(s)
- R H Gavin
- Department of Biology, Brooklyn College, City University of New York, New York 11210, USA
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13
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Peyser YM, Ajtai K, Burghardt TP, Muhlrad A. Effect of ionic strength on the conformation of myosin subfragment 1-nucleotide complexes. Biophys J 2001; 81:1101-14. [PMID: 11463651 PMCID: PMC1301579 DOI: 10.1016/s0006-3495(01)75767-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The effect of ionic strength on the conformation and stability of S1 and S1-nucleotide-phosphate analog complexes in solution was studied. It was found that increasing concentration of KCl enhances the reactivity of Cys(707) (SH1 thiol) and Lys(84) (reactive lysyl residue) and the nucleotide-induced tryptophan fluorescence increment. In contrast, high KCl concentration lowers the structural differences between the intermediate states of ATP hydrolysis in the vicinity of Cys(707), Trp(510) and the active site, possibly by increasing the flexibility of the molecule. High concentrations of neutral salts inhibit both the formation and the dissociation of the M**.ADP.Pi analog S1.ADP.Vi complex. High ionic strength profoundly affects the structure of the stable S1.ADP.BeF(x) complex, by destabilizing the M*.ATP intermediate, which is the predominant form of the complex at low ionic strength, and shifting the equilibrium to favor the M**.ADP.Pi state. The M*.ATP intermediate is destabilized by perturbation of ionic interactions possibly by disruption of salt bridges. Two salt-bridge pairs, Glu(501)-Lys(505) in the Switch II helix and Glu(776)-Lys(84) connecting the catalytic domain to the lever arm, seem most appropriate to consider for participating in the ionic strength-induced transition of the open M*.ATP to the closed M**.ADP.Pi state of S1.
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Affiliation(s)
- Y M Peyser
- Hebrew University Hadassah School of Dental Medicine, Institute of Dental Sciences, Department of Oral Biology, Jerusalem 91120, Israel
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Kinosita K. Linear and rotary molecular motors. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2001; 453:5-13; discussion 13-4. [PMID: 9889809 DOI: 10.1007/978-1-4684-6039-1_2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
A single molecule of F1-ATPase has been shown to be the smallest rotary motor ever found, with a central rotor of radius approximately 1 nm turning in a stator barrel of radius approximately 5 nm. Continuous rotation of the central gamma subunit was revealed under an optical microscope by attaching to gamma a huge marker, an actin filament. In a separate study, rotation of a sliding actin filament around its axis has been revealed by attaching a small probe, a single fluorescent dye molecule, to the actin filament and detecting the orientation of the fluorophore, and thus of the actin filament, through polarization imaging. The axial rotation was slow compared to the linear sliding, indicating that myosin does not 'walk' along the helical array of actin protomers but 'runs,' skipping many protomers. The two motors above, one rotary and the other linear, represent two extreme cases of the mode of motor operation: in the F1-ATPase the two partners, the rotor and stator, never detach from each other whereas myosin touches actin only occasionally. In considering the mechanisms of these and other molecular motors, distinction between bending and binding is important. The use of huge and small probes as described above should be useful in studies of protein machines in general, as a means of detecting conformational changes in a single protein molecule during function.
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Affiliation(s)
- K Kinosita
- Department of Physics, Faculty of Science and Technology, Keio University, Yokohama, Japan
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15
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Yam JW, Chan KW, Hsiao WL. Suppression of the tumorigenicity of mutant p53-transformed rat embryo fibroblasts through expression of a newly cloned rat nonmuscle myosin heavy chain-B. Oncogene 2001; 20:58-68. [PMID: 11244504 DOI: 10.1038/sj.onc.1203982] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2000] [Revised: 10/03/2000] [Accepted: 10/04/2000] [Indexed: 11/08/2022]
Abstract
In our previous study, a rat homolog of human nonmuscle myosin heavy chain-B (nmMHC-B) was identified by mRNA differential display comparing of transformed against nontransformed Rat 6 cells overexpressing mutant p53val135 gene. The nmMHC-B was found to be expressed in normal Rat 6 embryo fibroblast cell line, but markedly suppressed in the mutant p53val135-transformed Rat 6 cells. To examine the possible involvement of nmMHC-B in cell transformation, we first cloned and sequenced the full length cDNA of rat nmMHC-B, which was then cloned into an ecdysone-expression vector. The resulting construct was introduced into the T2 cell line, a mutant p53val135-transformed Rat 6 cells lacking the expression of the endogenous nmMHC-B. The clonal transfectants, expressing muristerone A-induced nmMHC-B, displayed a slightly flatter morphology and reached to a lower saturation density compared to the parental transformed cells. Reconstitution of actin filamental bundles was also clearly seen in cells overexpressing the nmMHC-B. In soft agar assays, nmMHC-B transfectants formed fewer and substantially smaller colonies than the parental cells in response to muristerone A induction. Moreover, it was strikingly effective in suppressing the tumorigenicity of the T2 cells when tested in nude mice. Thus, the nmMHC-B, known as a component of the cytoskeletal network, may act as a tumor suppressor gene. Our current finding may reveal a novel role of nmMHC-B in regulating cell growth and cell signaling in nonmuscle cells. Oncogene (2001) 20, 58 - 68.
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MESH Headings
- Actins/metabolism
- Amino Acid Sequence
- Animals
- Antineoplastic Agents/metabolism
- Antineoplastic Agents/pharmacology
- Cell Adhesion/genetics
- Cell Count
- Cell Line, Transformed
- Cell Transformation, Neoplastic/genetics
- Cell Transformation, Neoplastic/pathology
- Cloning, Molecular
- DNA, Complementary/isolation & purification
- Embryo, Mammalian
- Fibroblasts/metabolism
- Fibroblasts/pathology
- Fluorescent Antibody Technique, Indirect
- Gene Expression Regulation, Neoplastic
- Genes, p53
- Genetic Vectors/biosynthesis
- Genetic Vectors/chemical synthesis
- Growth Inhibitors/biosynthesis
- Growth Inhibitors/genetics
- Growth Inhibitors/physiology
- Humans
- Mice
- Mice, Nude
- Molecular Motor Proteins
- Molecular Sequence Data
- Mutation
- Myosin Heavy Chains/antagonists & inhibitors
- Myosin Heavy Chains/biosynthesis
- Myosin Heavy Chains/genetics
- Myosin Heavy Chains/physiology
- Nonmuscle Myosin Type IIB
- Protein Isoforms/antagonists & inhibitors
- Protein Isoforms/biosynthesis
- Protein Isoforms/genetics
- Rats
- Transfection
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Affiliation(s)
- J W Yam
- Department of Biology, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
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16
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Lalwani AK, Goldstein JA, Kelley MJ, Luxford W, Castelein CM, Mhatre AN. Human nonsyndromic hereditary deafness DFNA17 is due to a mutation in nonmuscle myosin MYH9. Am J Hum Genet 2000; 67:1121-8. [PMID: 11023810 PMCID: PMC1288554 DOI: 10.1016/s0002-9297(07)62942-5] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2000] [Accepted: 09/13/2000] [Indexed: 12/01/2022] Open
Abstract
The authors had previously mapped a new locus-DFNA17, for nonsyndromic hereditary hearing impairment-to chromosome 22q12.2-q13. 3. DFNA17 spans a 17- to 23-cM region, and MYH9, a nonmuscle-myosin heavy-chain gene, is located within the linked region. Because of the importance of myosins in hearing, MYH9 was tested as a candidate gene for DFNA17. Expression of MYH9 in the rat cochlea was confirmed using reverse transcriptase-PCR and immunohistochemistry. MYH9 was immunolocalized in the organ of Corti, the subcentral region of the spiral ligament, and the Reissner membrane. Sequence analysis of MYH9 in a family with DFNA17 identified, at nucleotide 2114, a G-->A transposition that cosegregated with the inherited autosomal dominant hearing impairment. This missense mutation changes codon 705 from an invariant arginine (R) to histidine (H), R705H, within a highly conserved SH1 linker region. Previous studies have shown that modification of amino acid residues within the SH1 helix causes dysfunction of the ATPase activity of the motor domain in myosin II. Both the precise role of MYH9 in the cochlea and the mechanism by which the R705H mutation leads to the DFNA17 phenotype (progressive hearing impairment and cochleosaccular degeneration) remain to be elucidated.
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Affiliation(s)
- A K Lalwani
- Laboratory of Molecular Otology, Epstein Laboratories, Department of Otolaryngology-Head and Neck Surgery, University of California, San Francisco, San Francisco, CA 94143, USA.
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Lalwani AK, Goldstein JA, Kelley MJ, Luxford W, Castelein CM, Mhatre AN. Human Nonsyndromic Hereditary Deafness DFNA17 Is Due to a Mutation in Nonmuscle MyosinMYH9. Am J Hum Genet 2000. [DOI: 10.1086/321212] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
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18
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Houdusse A, Szent-Gyorgyi AG, Cohen C. Three conformational states of scallop myosin S1. Proc Natl Acad Sci U S A 2000; 97:11238-43. [PMID: 11016966 PMCID: PMC17184 DOI: 10.1073/pnas.200376897] [Citation(s) in RCA: 274] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have determined the structure of the intact scallop myosin head, containing both the motor domain and the lever arm, in the nucleotide-free state and in the presence of MgADP.V04, corresponding to the transition state. These two new structures, together with the previously determined structure of scallop S1 complexed with MgADP (which we interpret as a detached ATP state), reveal three conformations of an intact S1 obtained from a single isoform. These studies, together with new crystallization results, show how the conformation of the motor depends on the nucleotide content of the active site. The resolution of the two new structures ( approximately 4 A) is sufficient to establish the relative positions of the subdomains and the overall conformation of the joints within the motor domain as well as the position of the lever arm. Comparison of available crystal structures from different myosin isoforms and truncated constructs in either the nucleotide-free or transition states indicates that the major features within the motor domain are relatively invariant in both these states. In contrast, the position of the lever arm varies significantly between different isoforms. These results indicate that the heavy-chain helix is pliant at the junction between the converter and the lever arm and that factors other than the precise position of the converter can influence the position of the lever arm. It is possible that this pliant junction in the myosin head contributes to the compliance known to be present in the crossbridge.
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Affiliation(s)
- A Houdusse
- Rosenstiel Basic Medical Sciences Research Center, and Biology Department, Brandeis University, Waltham, MA 02254-9110, USA.
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19
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Yasunaga T, Suzuki Y, Ohkura R, Sutoh K, Wakabayashi T. ATP-induced transconformation of myosin revealed by determining three-dimensional positions of fluorophores from fluorescence energy transfer measurements. J Struct Biol 2000; 132:6-18. [PMID: 11121303 DOI: 10.1006/jsbi.2000.4302] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The method of fluorescence resonance energy transfer (FRET) is one of the most important techniques for measuring the distance between two fluorophores and for detecting the changes in protein structure under physiological conditions. The use of green fluorescent protein is also a powerful technology that has been used to elucidate dynamic molecular events. From these we have developed a novel method to determine the three-dimensional positions of fluorophores by combining the FRET data and other structural information available. Using this method, we could determine the ATP-induced changes of three-dimensional structure of truncated Dictyostelium myosin in solution. The myosin structure with ADP in solution was found to be similar to that of the crystal structure of MgADPBeFx-bound truncated Dictyostelium myosin (type I structure), whereas myosin with ATP in solution was similar to the crystal structure of MgAdPVi-bound one (type II structure). However, the crystal structure of MgADP-bound scallop myosin (type III structure) could not be explained by any of our FRET data under various conditions. This indicates that the type III crystal structure might represent a transient intermediate conformation that could not be detected using fluorescence energy transfer.
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Affiliation(s)
- T Yasunaga
- Department of Physics, School of Science, University of Tokyo, 7-3-1, Hongo, Bunkyo, Tokyo 113-0033, Japan
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20
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Yamashita H, Tyska MJ, Warshaw DM, Lowey S, Trybus KM. Functional consequences of mutations in the smooth muscle myosin heavy chain at sites implicated in familial hypertrophic cardiomyopathy. J Biol Chem 2000; 275:28045-52. [PMID: 10882745 DOI: 10.1074/jbc.m005485200] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Familial hypertrophic cardiomyopathy (FHC) is frequently associated with mutations in the beta-cardiac myosin heavy chain. Many of the implicated residues are located in highly conserved regions of the myosin II class, suggesting that these mutations may impair the basic functions of the molecular motor. To test this hypothesis, we have prepared recombinant smooth muscle heavy meromyosin with mutations at sites homologous to those associated with FHC by using a baculovirus/insect cell expression system. Several of the heavy meromyosin mutants, in particular R403Q, showed an increase in actin filament velocity in a motility assay and an enhanced actin-activated ATPase activity. Single molecule mechanics, using a laser trap, gave unitary displacements and forces for the mutants that were similar to wild type, but the attachment times to actin following a unitary displacement were markedly reduced. These results suggest that the increases in activity are due to a change in kinetics and not due to a change in the intrinsic mechanical properties of the motor. In contrast to earlier reports, we find that mutations in residues implicated in FHC affect motor function by enhancing myosin activity rather than by a loss of function.
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MESH Headings
- Actins/metabolism
- Amino Acid Sequence
- Amino Acid Substitution
- Animals
- Binding Sites
- Cardiomyopathy, Hypertrophic/genetics
- Cardiomyopathy, Hypertrophic/metabolism
- Chickens
- Conserved Sequence
- Crystallography, X-Ray
- Gizzard, Avian
- Humans
- Kinetics
- Models, Molecular
- Muscle, Smooth/metabolism
- Muscle, Smooth, Vascular/metabolism
- Mutagenesis, Site-Directed
- Myocardium/metabolism
- Myosin Heavy Chains/chemistry
- Myosin Heavy Chains/genetics
- Myosin Heavy Chains/metabolism
- Myosins/chemistry
- Myosins/genetics
- Myosins/metabolism
- Point Mutation
- Protein Conformation
- Protein Structure, Secondary
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Affiliation(s)
- H Yamashita
- Department of Cardiovascular Medicine, Graduate School of Medicine, University of Tokyo, Tokyo 113-8655, Japan
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21
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Yengo CM, Chrin LR, Rovner AS, Berger CL. Tryptophan 512 is sensitive to conformational changes in the rigid relay loop of smooth muscle myosin during the MgATPase cycle. J Biol Chem 2000; 275:25481-7. [PMID: 10827189 DOI: 10.1074/jbc.m002910200] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To examine the structural basis of the intrinsic fluorescence changes that occur during the MgATPase cycle of myosin, we generated three mutants of smooth muscle myosin motor domain essential light chain (MDE) containing a single conserved tryptophan residue located at Trp-441 (W441-MDE), Trp-512 (W512-MDE), or Trp-597 (W597-MDE). Although W441- and W597-MDE were insensitive to nucleotide binding, the fluorescence intensity of W512-MDE increased in the presence of MgADP-berellium fluoride (BeF(X)) (31%), MgADP-AlF(4)(-) (31%), MgATP (36%), and MgADP (30%) compared with the nucleotide-free environment (rigor), which was similar to the results of wild type-MDE. Thus, Trp-512 may be the sole ATP-sensitive tryptophan residue in myosin. In addition, acrylamide quenching indicated that Trp-512 was more protected from solvent in the presence of MgATP or MgADP-AlF(4)(-) than in the presence of MgADP-BeF(X), MgADP, or in rigor. Furthermore, the degree of energy transfer from Trp-512 to 2'(3')-O-(N-methylanthraniloyl)-labeled nucleotides was greater in the presence of MgADP-BeF(X), MgATP, or MgADP-AlF(4)(-) than MgADP. We conclude that the conformation of the rigid relay loop containing Trp-512 is altered upon MgATP hydrolysis and during the transition from weak to strong actin binding, establishing a communication pathway from the active site to the actin-binding and converter/lever arm regions of myosin during muscle contraction.
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Affiliation(s)
- C M Yengo
- Department of Molecular Physiology and Biophysics, College of Medicine, University of Vermont, Burlington 05405-0068, USA
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22
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Abstract
X-ray crystallography shows the myosin cross-bridge to exist in two conformations, the beginning and end of the "power stroke." A long lever-arm undergoes a 60 degrees to 70 degrees rotation between the two states. This rotation is coupled with changes in the active site (OPEN to CLOSED) and phosphate release. Actin binding mediates the transition from CLOSED to OPEN. Kinetics shows that the binding of myosin to actin is a two-step process which affects ATP and ADP affinity. The structural basis of these effects is not explained by the presently known conformers of myosin. Therefore, other states of the myosin cross-bridge must exist. Moreover, cryoelectronmicroscopy has revealed other angles of the cross-bridge lever arm induced by ADP binding. These structural states are presently being characterized by site-directed mutagenesis coupled with kinetic analysis.
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Affiliation(s)
- M A Geeves
- Department of Biosciences, University of Kent, Canterbury, United Kingdom.
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23
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Becker EW. Kinetic equilibrium of forces and molecular events in muscle contraction. Proc Natl Acad Sci U S A 2000; 97:157-61. [PMID: 10618387 PMCID: PMC26632 DOI: 10.1073/pnas.97.1.157] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/1999] [Accepted: 11/08/1999] [Indexed: 12/27/2022] Open
Abstract
In biomolecular systems, the mechanical transfer of free energy occurs with both high efficiency and high speed. It is shown here that such a transfer can be achieved only if the participating free-energy-storing elements exhibit opposing relationships between their content of free energy and the force they exert in the transfer direction. A kinetic equilibrium of forces (KEF) results, in which the transfer of free energy is mediated essentially by thermal molecular motion. On the basis of present evidence, KEF is used as a guiding principle in developing a mechanical model of the crossbridge cycle in muscle contraction. The model allows the basic features of molecular events to be visualized in terms of plausible structures. Real understanding of the process will require identification of the elements that perform the functions described here. Besides chemomechanical energy transduction, KEF may have a role in other biomolecular processes in which free energy is transferred mechanically over large distances.
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Affiliation(s)
- E W Becker
- Institut für Mikrostrukturtechnik, Forschungszentrum, and Universität Karlsruhe, 76021 Karlsruhe, Germany.
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24
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Wendt T, Taylor D, Messier T, Trybus KM, Taylor KA. Visualization of head-head interactions in the inhibited state of smooth muscle myosin. J Cell Biol 1999; 147:1385-90. [PMID: 10613897 PMCID: PMC2174251 DOI: 10.1083/jcb.147.7.1385] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The structural basis for the phosphoryla- tion-dependent regulation of smooth muscle myosin ATPase activity was investigated by forming two- dimensional (2-D) crystalline arrays of expressed unphosphorylated and thiophosphorylated smooth muscle heavy meromyosin (HMM) on positively charged lipid monolayers. A comparison of averaged 2-D projections of both forms at 2.3-nm resolution reveals distinct structural differences. In the active, thiophosphorylated form, the two heads of HMM interact intermolecularly with adjacent molecules. In the unphosphorylated or inhibited state, intramolecular interactions position the actin-binding interface of one head onto the converter domain of the second head, thus providing a mechanism whereby the activity of both heads could be inhibited.
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Affiliation(s)
- Thomas Wendt
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306
| | - Dianne Taylor
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306
| | - Terri Messier
- Department of Molecular Physiology and Biophysics, University of Vermont College of Medicine, Burlington, Vermont 05405
| | - Kathleen M. Trybus
- Department of Molecular Physiology and Biophysics, University of Vermont College of Medicine, Burlington, Vermont 05405
| | - Kenneth A. Taylor
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306
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25
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Taylor KA, Schmitz H, Reedy MC, Goldman YE, Franzini-Armstrong C, Sasaki H, Tregear RT, Poole K, Lucaveche C, Edwards RJ, Chen LF, Winkler H, Reedy MK. Tomographic 3D reconstruction of quick-frozen, Ca2+-activated contracting insect flight muscle. Cell 1999; 99:421-31. [PMID: 10571184 DOI: 10.1016/s0092-8674(00)81528-7] [Citation(s) in RCA: 135] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Motor actions of myosin were directly visualized by electron tomography of insect flight muscle quick-frozen during contraction. In 3D images, active cross-bridges are usually single myosin heads, bound preferentially to actin target zones sited midway between troponins. Active attached bridges (approximately 30% of all heads) depart markedly in axial and azimuthal angles from Rayment's rigor acto-S1 model, one-third requiring motor domain (MD) tilting on actin, and two-thirds keeping rigor contact with actin while the light chain domain (LCD) tilts axially from approximately 105 degrees to approximately 70 degrees. The results suggest the MD tilts and slews on actin from weak to strong binding, followed by swinging of the LCD through an approximately 35 degrees axial angle, giving an approximately 13 nm interaction distance and an approximately 4-6 nm working stroke.
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Affiliation(s)
- K A Taylor
- Institute of Molecular Biophysics, Florida State University, Tallahassee, 32306-4380, USA.
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26
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Yan D, Kustu S. "Switch I" mutant forms of the bacterial enhancer-binding protein NtrC that perturb the response to DNA. Proc Natl Acad Sci U S A 1999; 96:13142-6. [PMID: 10557287 PMCID: PMC23914 DOI: 10.1073/pnas.96.23.13142] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
NtrC (nitrogen regulatory protein C) is a bacterial enhancer-binding protein of 469 residues that activates transcription by sigma(54)-holoenzyme. A region of its transcriptional activation (central) domain that is highly conserved among homologous activators of sigma(54)-holoenzyme-residues 206-220-is essential for interaction with this RNA polymerase: it is required for contact with the polymerase and/or for coupling the energy from ATP hydrolysis to a change in the conformation of the polymerase that allows it to form transcriptionally productive open complexes. Several mutant NtrC proteins with amino acid substitutions in this region, including NtrC(A216V) and NtrC(G219K), have normal ATPase activity but fail in transcriptional activation. We now report that other mutant forms carrying amino acid substitutions at these same positions, NtrC(A216C) and NtrC(G219C), are capable of activating transcription when they are not bound to a DNA template (non-DNA-binding derivatives with an altered helix-turn-helix DNA-binding motif at the C terminus of the protein) but are unable to do so when they are bound to a DNA template, whether or not it carries a specific enhancer. Enhancer DNA remains a positive allosteric effector of ATP hydrolysis, as it is for wild-type NtrC but, surprisingly, appears to have become a negative allosteric effector for some aspect of interaction with sigma(54)-holoenzyme. The conserved region in which these amino acid substitutions occur (206-220) is equivalent to the Switch I region of a large group of purine nucleotide-binding proteins. Interesting analogies can be drawn between the Switch I region of NtrC and that of p21(ras).
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Affiliation(s)
- D Yan
- Department of Plant Biology, University of California, Berkeley, CA 94720-3102, USA
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27
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Abstract
The folding pathway of the heavy meromyosin subfragment (HMM) of a skeletal muscle myosin has been investigated by in vitro synthesis of the myosin heavy and light chains in a coupled transcription and translation assay. Analysis of the nascent translation products for folding intermediates has identified a major intermediate that contains all three myosin subunits in a complex with the eukaryotic cytosolic chaperonin. Partially folded HMM is released from this complex in an ATP-dependent manner. However, biochemical and functional assays reveal incomplete folding of the myosin motor domain. Dimerization of myosin heavy chains and association of heavy and light chains are accomplished early in the folding pathway. To test for other factors necessary for the complete folding of myosin, a cytoplasmic extract was prepared from myotubes produced by a mouse myogenic cell line. This extract dramatically enhanced the folding of HMM, suggesting a role for muscle-specific factors in the folding pathway. We conclude that the molecular assembly of myosin is mediated by the eukaryotic cytosolic chaperonin with folding of the motor domain as the slow step in the pathway.
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Affiliation(s)
- R Srikakulam
- Department of Pathology and Laboratory Medicine, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA
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28
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Houdusse A, Kalabokis VN, Himmel D, Szent-Györgyi AG, Cohen C. Atomic structure of scallop myosin subfragment S1 complexed with MgADP: a novel conformation of the myosin head. Cell 1999; 97:459-70. [PMID: 10338210 DOI: 10.1016/s0092-8674(00)80756-4] [Citation(s) in RCA: 259] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The crystal structure of a proteolytic subfragment from scallop striated muscle myosin, complexed with MgADP, has been solved at 2.5 A resolution and reveals an unusual conformation of the myosin head. The converter and the lever arm are in very different positions from those in either the pre-power stroke or near-rigor state structures; moreover, in contrast to these structures, the SH1 helix is seen to be unwound. Here we compare the overall organization of the myosin head in these three states and show how the conformation of three flexible "joints" produces rearrangements of the four major subdomains in the myosin head with different bound nucleotides. We believe that this novel structure represents one of the prehydrolysis ("ATP") states of the contractile cycle in which the myosin heads stay detached from actin.
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Affiliation(s)
- A Houdusse
- Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02254-9110, USA
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29
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Sack S, Kull FJ, Mandelkow E. Motor proteins of the kinesin family. Structures, variations, and nucleotide binding sites. EUROPEAN JOURNAL OF BIOCHEMISTRY 1999; 262:1-11. [PMID: 10231357 DOI: 10.1046/j.1432-1327.1999.00341.x] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Microtubule-dependent motors of the kinesin family convert the energy from ATP hydrolysis into mechanical work in order to transport vesicles and organelles along microtubules. The motor domains of several kinesins have been solved by X-ray diffraction, but the conformational changes associated with force development remain unknown. Here we describe conformational properties of kinesin that might be related to the mechanism of action. First, we have evaluated the conformational variability among all known kinesin structures and find they are concentrated in six areas, most of which are functionally important either in microtubule binding or in linking the core motor to the stalk. Secondly, we show that there is an important difference between kinesins when compared with myosins or GTPases (with which kinesin motor domains bear structural and catalytic similarities); in the diphosphate-state (with bound ADP), all kinesins show a 'tight' nucleotide-binding pocket, comparable with myosin or GTPases in the triphosphate state, whose nucleotide-binding pockets become open, or 'loose', following nucleotide hydrolysis. Thus, kinesin-ADP appears to be in a tense state, resembling that observed in myosin-ATP or p21ras-GTP.
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Affiliation(s)
- S Sack
- Max-Planck-Unit for Structural Molecular Biology, Hamburg, Germany
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30
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Abstract
Several X-ray crystal structures of kinesin motor domains have recently been solved at high resolution ( approximately 0.2-0.3 nm), in both their monomeric and dimeric states. They show the folding of the polypeptide chain and different arrangements of subunits in the dimer. In addition, cryo-electron microscopy and image reconstruction have revealed microtubules decorated with kinesin at intermediate resolution ( approximately 2 nm), showing the distribution and orientation of kinesin heads on the microtubule surface. The comparison of the X-ray and electron microscopy results yields a model of how monomeric motor domains bind to the microtubule but the binding of dimeric motors, their stoichiometry, or the influence of nucleotides remains a matter of debate.
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Affiliation(s)
- E Mandelkow
- Max-Planck-Unit for Structural Molecular Biology Notkestrasse 85 D-22607 Hamburg Germany.
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31
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Abstract
Kinesin is a microtubule-based motor protein that pulls vesicles or organelles towards the plus end of microtubules. Structural changes in the protein that drive motility are coupled to ATP binding and hydrolysis. Here, we attempt to integrate recent structural and kinetic results into a picture of the mechanochemical cycle of kinesin.
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Affiliation(s)
- E Mandelkow
- Max Planck Unit for Structural Molecular Biology, Hamburg, Germany.
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32
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Rushforth AM, White CC, Anderson P. Functions of the Caenorhabditis elegans regulatory myosin light chain genes mlc-1 and mlc-2. Genetics 1998; 150:1067-77. [PMID: 9799259 PMCID: PMC1460388 DOI: 10.1093/genetics/150.3.1067] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Caenorhabditis elegans contains two muscle regulatory myosin light chain genes, mlc-1 and mlc-2. To determine their in vivo roles, we identified deletions that eliminate each gene individually and both genes in combination. Functions of mlc-1 are redundant to those of mlc-2 in both body-wall and pharyngeal muscle. mlc-1(0) mutants are wild type, but mlc-1(0) mlc-2(0) double mutants arrest as incompletely elongated L1 larvae, having both pharyngeal and body-wall muscle defects. Transgenic copies of either mlc-1(+) or mlc-2(+) rescue all defects of mlc-1(0) mlc-2(0) double mutants. mlc-2 is redundant to mlc-1 in body-wall muscle, but mlc-2 performs a nearly essential role in the pharynx. Approximately 90% of mlc-2(0) hermaphrodites arrest as L1 larvae due to pharyngeal muscle defects. Lethality of mlc-2(0) mutants is sex specific, with mlc-2(0) males being essentially wild type. Four observations suggest that hermaphrodite-specific lethality of mlc-2(0) mutants results from insufficient expression of the X-linked mlc-1(+) gene in the pharynx. First, mlc-1(0) mlc-2(0) double mutants are fully penetrant L1 lethals in both hermaphrodites and males. Second, in situ localization of mlc mRNAs demonstrates that both mlc-1 and mlc-2 are expressed in the pharynx. Third, transgenic copies of either mlc-1(+) or mlc-2(+) rescue the pharyngeal defects of mlc-1(0) mlc-2(0) hermaphrodites. Fourth, a mutation of the dosage compensation gene sdc-3 suppresses hermaphrodite-specific lethality of mlc-2(0) mutants.
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Affiliation(s)
- A M Rushforth
- Department of Genetics, University of Wisconsin, Madison, Wisconsin 53706, USA
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33
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Dominguez R, Freyzon Y, Trybus KM, Cohen C. Crystal structure of a vertebrate smooth muscle myosin motor domain and its complex with the essential light chain: visualization of the pre-power stroke state. Cell 1998; 94:559-71. [PMID: 9741621 DOI: 10.1016/s0092-8674(00)81598-6] [Citation(s) in RCA: 505] [Impact Index Per Article: 19.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The crystal structures of an expressed vertebrate smooth muscle myosin motor domain (MD) and a motor domain-essential light chain (ELC) complex (MDE), both with a transition state analog (MgADP x AIF4-) in the active site, have been determined to 2.9 A and 3.5 A resolution, respectively. The MDE structure with an ATP analog (MgADP x BeFx) was also determined to 3.6 A resolution. In all three structures, a domain of the C-terminal region, the "converter," is rotated approximately 70 degrees from that in nucleotide-free skeletal subfragment 1 (S1). We have found that the MDE-BeFx and MDE-AIF4- structures are almost identical, consistent with the fact that they both bind weakly to actin. A comparison of the lever arm positions in MDE-AIF4- and in nucleotide-free skeletal S1 shows that a potential displacement of approximately 10 nm can be achieved during the power stroke.
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Affiliation(s)
- R Dominguez
- Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02454-9110, USA
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34
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Katayama E. Quick-freeze deep-etch electron microscopy of the actin-heavy meromyosin complex during the in vitro motility assay. J Mol Biol 1998; 278:349-67. [PMID: 9571057 DOI: 10.1006/jmbi.1998.1715] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Since mica is a substitute for glass in the in vitro actin motility assay, I examined the structure of heavy meromyosin (HMM) crossbridges supporting actin filaments by quick-freeze deep-etch replica electron microscopy. This method was capable of resolving the inter-domain cleft of the monomeric actin molecule. HMM heads that are not bound to actin, when observed by this technique, were straight and elongated in the absence of ATP but strongly kinked upon addition of ATP or ADP.inorganic vanadate to produce the putative long-lived analog of HMM-ADP.inorganic phosphate. The low-magnification image of the ATP-containing acto-HMM preparation showed features characteristic of sliding actin filaments on glass coverslips. At high magnification, all the HMM molecules were found attached to actin by one head with the majority projecting perpendicular to the filament axis, whereas in the absence of ATP, HMM exhibited two-head binding with a preponderance of molecules tilted at 45 degrees. Detailed examination of the shape of HMM heads involved in sliding showed a rounded, and flat appearance of the tip and comparatively thin neck portion as if the heads grasp actin filament, in contrast to rigor crossbridges which have a pear-shaped configuration with more gradual taper. Such configurations of HMM heads were essentially the same as I observed previously on acto-myosin subfragment-1 (S1) by the same technique, except for the presence of an additional neck portion of HMM which makes interpretaion of the images easier. Interestingly, under actively sliding conditions, very few heads were tilted in the rigor configuration. At first glance, the addition of ADP to the rigor-complex gave images rather like those obtained with ATP, but they turned out to be different. The contribution of the structural change of crossbridges to the force development is discussed.
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Affiliation(s)
- E Katayama
- Institute of Medical Science, The University of Tokyo, Minato-ku, Tokyo, 108, Japan
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35
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Affiliation(s)
- K Kinosita
- Department of Physics, Faculty of Science and Technology, Keio University, Yokohama, Japan
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36
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Mermall V, Post PL, Mooseker MS. Unconventional myosins in cell movement, membrane traffic, and signal transduction. Science 1998; 279:527-33. [PMID: 9438839 DOI: 10.1126/science.279.5350.527] [Citation(s) in RCA: 524] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
In the past few years genetic, biochemical, and cytolocalization data have implicated members of the myosin superfamily of actin-based molecular motors in a variety of cellular functions including membrane trafficking, cell movements, and signal transduction. The importance of myosins is illustrated by the identification of myosin genes as targets for disease-causing mutations. The task at hand is to decipher how the multitude of myosins function at both the molecular and cellular level-a task facilitated by our understanding of myosin structure and function in muscle.
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Affiliation(s)
- V Mermall
- Department of Biology, Yale University 342 KBT, New Haven, CT 06520, USA
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