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McMillan SN, Scarff CA. Cryo-electron microscopy analysis of myosin at work and at rest. Curr Opin Struct Biol 2022; 75:102391. [DOI: 10.1016/j.sbi.2022.102391] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2022] [Revised: 04/18/2022] [Accepted: 04/22/2022] [Indexed: 01/01/2023]
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2
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Klebl DP, White HD, Sobott F, Muench SP. On-grid and in-flow mixing for time-resolved cryo-EM. Acta Crystallogr D Struct Biol 2021; 77:1233-1240. [PMID: 34605427 PMCID: PMC8489233 DOI: 10.1107/s2059798321008810] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Accepted: 08/23/2021] [Indexed: 02/06/2023] Open
Abstract
Time-resolved cryo-electron microscopy (TrEM) allows the study of proteins under non-equilibrium conditions on the millisecond timescale, permitting the analysis of large-scale conformational changes or assembly and disassembly processes. However, the technique is developing and there have been few comparisons with other biochemical kinetic studies. Using current methods, the shortest time delay is on the millisecond timescale (∼5-10 ms), given by the delay between sample application and vitrification, and generating longer time points requires additional approaches such as using a longer delay line between the mixing element and nozzle, or an incubation step on the grid. To compare approaches, the reaction of ATP with the skeletal actomyosin S1 complex was followed on grids prepared with a 7-700 ms delay between mixing and vitrification. Classification of the cryo-EM data allows kinetic information to be derived which agrees with previous biochemical measurements, showing fast dissociation, low occupancy during steady-state hydrolysis and rebinding once ATP has been hydrolysed. However, this rebinding effect is much less pronounced when on-grid mixing is used and may be influenced by interactions with the air-water interface. Moreover, in-flow mixing results in a broader distribution of reaction times due to the range of velocities in a laminar flow profile (temporal spread), especially for longer time delays. This work shows the potential of TrEM, but also highlights challenges and opportunities for further development.
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Affiliation(s)
- David P. Klebl
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom
- Astbury Centre for Structural and Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Howard D. White
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia, USA
| | - Frank Sobott
- Astbury Centre for Structural and Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
- School of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Stephen P. Muench
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom
- Astbury Centre for Structural and Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
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3
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Xie P. Dynamics of ATP-dependent and ATP-independent steppings of myosin-V on actin: catch-bond characteristics. J R Soc Interface 2020; 17:20200029. [PMID: 32259459 PMCID: PMC7211485 DOI: 10.1098/rsif.2020.0029] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Accepted: 03/17/2020] [Indexed: 11/22/2022] Open
Abstract
An analytical theory is presented for the dynamics of myosin-V molecular motor, where both ATP-dependent and ATP-independent steppings are taken into account. Specifically, the dependences of velocity, run length and unbinding rate upon both forward and backward loads and ATP concentration are studied, explaining quantitatively the diverse available single-molecule data and providing predicted results. The results show that the unbinding rate increases with the increase of ATP concentration and levels off at both low and high ATP concentrations. More interestingly, at an ATP concentration that is not very low, the unbinding rate exhibits characteristics of a catch-slip bond under backward load, with the unbinding rate decreasing rapidly with the increase of the backward load in the range smaller than about 2.5 pN and then increasing slowly with the further increase of the backward load. By contrast, under forward load the unbinding rate exhibits a slip-bond characteristic.
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Affiliation(s)
- Ping Xie
- Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China
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4
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Klebl DP, Monteiro DCF, Kontziampasis D, Kopf F, Sobott F, White HD, Trebbin M, Muench SP. Sample deposition onto cryo-EM grids: from sprays to jets and back. Acta Crystallogr D Struct Biol 2020; 76:340-349. [PMID: 32254058 PMCID: PMC7137104 DOI: 10.1107/s2059798320002958] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Accepted: 03/03/2020] [Indexed: 11/11/2022] Open
Abstract
Despite the great strides made in the field of single-particle cryogenic electron microscopy (cryo-EM) in microscope design, direct electron detectors and new processing suites, the area of sample preparation is still far from ideal. Traditionally, sample preparation involves blotting, which has been used to achieve high resolution, particularly for well behaved samples such as apoferritin. However, this approach is flawed since the blotting process can have adverse effects on some proteins and protein complexes, and the long blot time increases exposure to the damaging air-water interface. To overcome these problems, new blotless approaches have been designed for the direct deposition of the sample on the grid. Here, different methods of producing droplets for sample deposition are compared. Using gas dynamic virtual nozzles, small and high-velocity droplets were deposited on cryo-EM grids, which spread sufficiently for high-resolution cryo-EM imaging. For those wishing to pursue a similar approach, an overview is given of the current use of spray technology for cryo-EM grid preparation and areas for enhancement are pointed out. It is further shown how the broad aspects of sprayer design and operation conditions can be utilized to improve grid quality reproducibly.
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Affiliation(s)
- David P. Klebl
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom
- Astbury Centre for Structural and Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Diana C. F. Monteiro
- The Hamburg Centre for Ultrafast Imaging, Universität Hamburg, Hamburg, Germany
- Hauptman–Woodward Medical Research Institute, Buffalo, New York, USA
| | - Dimitrios Kontziampasis
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom
- Astbury Centre for Structural and Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
- Institute of Business, Industry and Leadership, University of Cumbria, Carlisle CA1 2HH, United Kingdom
| | - Florian Kopf
- The Hamburg Centre for Ultrafast Imaging, Universität Hamburg, Hamburg, Germany
| | - Frank Sobott
- Astbury Centre for Structural and Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
- School of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
- Department of Chemistry, Biomolecular and Analytical Mass Spectrometry Group, University of Antwerp, Antwerp, Belgium
| | - Howard D. White
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia, USA
| | - Martin Trebbin
- Hauptman–Woodward Medical Research Institute, Buffalo, New York, USA
- Department of Chemistry, State University of New York at Buffalo, New York, USA
| | - Stephen P. Muench
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom
- Astbury Centre for Structural and Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
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5
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Abstract
After several decades studying different acto-myosin complexes at lower and intermediate resolution - limited by the electron microscope instrumentation available then - recent advances in imaging technology have been crucial for obtaining a number of excellent high-resolution 3D reconstructions from cryo electron microscopy. The resolution level reached now is about 3-4 Å, which allows unambiguous model building of filamentous actin on its own as well as that of actin filaments decorated with strongly bound myosin variants. The interface between actin and the myosin motor domain can now be described in detail, and the function of parts of the interface (such as, e.g., the cardiomyopathy loop) can be understood in a mechanistical way. Most recently, reconstructions of actin filaments decorated with different myosins, which show a strongly bound acto-myosin complex also in the presence of the nucleotide ADP, have become available. The comparison of these structures with the nucleotide-free Rigor state provide the first mechanistic description of force sensing. An open question is still the initial interaction of the motor domain of myosin with the actin filament. Such weakly interacting states have so far not been the subject of microscopical studies, even though high-resolution structures would be needed to shed light on the initial steps of phosphate release and power stroke initiation.
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6
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Xie P. A model for the chemomechanical coupling of myosin-V molecular motors. RSC Adv 2019; 9:26734-26747. [PMID: 35528596 PMCID: PMC9070430 DOI: 10.1039/c9ra05072h] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2019] [Accepted: 08/13/2019] [Indexed: 11/28/2022] Open
Abstract
Herein, a model for the chemomechanical coupling of dimeric myosin-V motors is presented. Based on this model and the proposal that the rate constants of the ATPase activity of the two heads are independent of an external force in a range smaller than the stall force, we analytically studied the dynamics of the motor, such as the stepping ratio, dwell time between two mechanical steps, and velocity, under varying force and ATP concentrations. The theoretical results well reproduce the diverse available single-molecule experimental data. In particular, the experimental data showing that at a low ATP concentration, the dwell time and velocity have less force dependency than at a high ATP concentration is explained quantitatively. Moreover, the dependency of the chemomechanical coupling ratio on the force and ATP concentration was studied. The paper presents a model of chemomechanical coupling of myosin-V motor, explaining the dynamics under varying force and ATP concentrations.![]()
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Affiliation(s)
- Ping Xie
- Key Laboratory of Soft Matter Physics
- Institute of Physics
- Chinese Academy of Sciences
- Beijing 100190
- China
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7
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Dillard RS, Hampton CM, Strauss JD, Ke Z, Altomara D, Guerrero-Ferreira RC, Kiss G, Wright ER. Biological Applications at the Cutting Edge of Cryo-Electron Microscopy. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2018; 24:406-419. [PMID: 30175702 PMCID: PMC6265046 DOI: 10.1017/s1431927618012382] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Cryo-electron microscopy (cryo-EM) is a powerful tool for macromolecular to near-atomic resolution structure determination in the biological sciences. The specimen is maintained in a near-native environment within a thin film of vitreous ice and imaged in a transmission electron microscope. The images can then be processed by a number of computational methods to produce three-dimensional information. Recent advances in sample preparation, imaging, and data processing have led to tremendous growth in the field of cryo-EM by providing higher resolution structures and the ability to investigate macromolecules within the context of the cell. Here, we review developments in sample preparation methods and substrates, detectors, phase plates, and cryo-correlative light and electron microscopy that have contributed to this expansion. We also have included specific biological applications.
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Affiliation(s)
- Rebecca S Dillard
- 1Division of Pediatric Infectious Diseases,Emory University School of Medicine,Children's Healthcare of Atlanta,Atlanta,GA 30322,USA
| | - Cheri M Hampton
- 1Division of Pediatric Infectious Diseases,Emory University School of Medicine,Children's Healthcare of Atlanta,Atlanta,GA 30322,USA
| | - Joshua D Strauss
- 1Division of Pediatric Infectious Diseases,Emory University School of Medicine,Children's Healthcare of Atlanta,Atlanta,GA 30322,USA
| | - Zunlong Ke
- 1Division of Pediatric Infectious Diseases,Emory University School of Medicine,Children's Healthcare of Atlanta,Atlanta,GA 30322,USA
| | - Deanna Altomara
- 1Division of Pediatric Infectious Diseases,Emory University School of Medicine,Children's Healthcare of Atlanta,Atlanta,GA 30322,USA
| | - Ricardo C Guerrero-Ferreira
- 1Division of Pediatric Infectious Diseases,Emory University School of Medicine,Children's Healthcare of Atlanta,Atlanta,GA 30322,USA
| | - Gabriella Kiss
- 1Division of Pediatric Infectious Diseases,Emory University School of Medicine,Children's Healthcare of Atlanta,Atlanta,GA 30322,USA
| | - Elizabeth R Wright
- 1Division of Pediatric Infectious Diseases,Emory University School of Medicine,Children's Healthcare of Atlanta,Atlanta,GA 30322,USA
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8
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Guhathakurta P, Prochniewicz E, Grant BD, Peterson KC, Thomas DD. High-throughput screen, using time-resolved FRET, yields actin-binding compounds that modulate actin-myosin structure and function. J Biol Chem 2018; 293:12288-12298. [PMID: 29866882 DOI: 10.1074/jbc.ra118.002702] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Revised: 05/16/2018] [Indexed: 12/20/2022] Open
Abstract
We have used a novel time-resolved FRET (TR-FRET) assay to detect small-molecule modulators of actin-myosin structure and function. Actin-myosin interactions play crucial roles in the generation of cellular force and movement. Numerous mutations and post-translational modifications of actin or myosin disrupt muscle function and cause life-threatening syndromes. Here, we used a FRET biosensor to identify modulators that bind to the actin-myosin interface and alter the structural dynamics of this complex. We attached a fluorescent donor to actin at Cys-374 and a nonfluorescent acceptor to a peptide containing the 12 N-terminal amino acids of the long isoform of skeletal muscle myosin's essential light chain. The binding site on actin of this acceptor-labeled peptide (ANT) overlaps with that of myosin, as indicated by (a) a similar distance observed in the actin-ANT complex as in the actin-myosin complex and (b) a significant decrease in actin-ANT FRET upon binding myosin. A high-throughput FRET screen of a small-molecule library (NCC, 727 compounds), using a unique fluorescence lifetime readout with unprecedented speed and precision, showed that FRET is significantly affected by 10 compounds in the micromolar range. Most of these "hits" alter actin-activated myosin ATPase and affect the microsecond dynamics of actin detected by transient phosphorescence anisotropy. We conclude that the actin-ANT TR-FRET assay enables detection of pharmacologically active compounds that affect actin structural dynamics and actomyosin function. This assay establishes feasibility for the discovery of allosteric modulators of the actin-myosin interaction, with the ultimate goal of developing therapies for muscle disorders.
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Affiliation(s)
- Piyali Guhathakurta
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
| | - Ewa Prochniewicz
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455
| | | | | | - David D Thomas
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455; Photonic Pharma LLC, Minneapolis, Minnesota 55410.
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9
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Katayama E, Kodera N. Unconventional Imaging Methods to Capture Transient Structures during Actomyosin Interaction. Int J Mol Sci 2018; 19:ijms19051402. [PMID: 29738465 PMCID: PMC5983842 DOI: 10.3390/ijms19051402] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2018] [Revised: 05/04/2018] [Accepted: 05/05/2018] [Indexed: 11/30/2022] Open
Abstract
Half a century has passed since the cross-bridge structure was recognized as the molecular machine that generates muscle tension. Despite various approaches by a number of scientists, information on the structural changes in the myosin heads, particularly its transient configurations, remains scant even now, in part because of their small size and rapid stochastic movements during the power stroke. Though progress in cryo-electron microscopy is eagerly awaited as the ultimate means to elucidate structural details, the introduction of some unconventional methods that provide high-contrast raw images of the target protein assemblies is quite useful, if available, to break the current impasse. Quick-freeze deep–etch–replica electron microscopy coupled with dedicated image analysis procedures, and high-speed atomic-force microscopy are two such candidates. We have applied the former to visualize actin-associated myosin heads under in vitro motility assay conditions, and found that they take novel configurations similar to the SH1–SH2-crosslinked myosin that we characterized recently. By incorporating biochemical and biophysical results, we have revised the cross-bridge mechanism to involve the new conformer as an important main player. The latter “microscopy” is unique and advantageous enabling continuous observation of various protein assemblies as they function. Direct observation of myosin-V’s movement along actin filaments revealed several unexpected behaviors such as foot-stomping of the leading head and unwinding of the coiled-coil tail. The potential contribution of these methods with intermediate spatial resolution is discussed.
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Affiliation(s)
- Eisaku Katayama
- Waseda Research Institute for Science and Engineering, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan.
| | - Noriyuki Kodera
- WPI Nano Life Science Institute, Kanazawa University, Kakuma-machi, Kanazawa, Ishikawa 920-1192, Japan.
- Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
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10
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Prochniewicz E, Guhathakurta P, Thomas DD. The structural dynamics of actin during active interaction with myosin depends on the isoform of the essential light chain. Biochemistry 2013; 52:1622-30. [PMID: 23339370 DOI: 10.1021/bi3014467] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
We have used time-resolved phosphorescence anisotropy to investigate the effects of essential light chain (ELC) isoforms (A1 and A2) on the interaction of skeletal muscle myosin with actin, to relate structural dynamics to previously reported functional effects. Actin was labeled with a phosphorescent probe at C374, and the myosin head (S1) was separated into isoenzymes S1A1 and S1A2 by ion-exchange chromatography. As previously reported, S1A1 exhibited substantially lower ATPase activity at saturating actin concentrations but substantially higher apparent actin affinity, resulting in a higher catalytic efficiency. In the absence of ATP, each isoenzyme increased actin's final anisotropy cooperatively and to a similar extent, indicating a similar restriction of the amplitude of intrafilament rotational motions in the strong-binding (S) state of actomyosin. In contrast, in the presence of a saturating level of ATP, S1A1 increased actin anisotropy much more than S1A2 and with greater cooperativity, indicating that S1A1 was more effective in restricting actin dynamics during the active interaction of actin and myosin. We conclude that during the active interaction of actin and ATP with myosin, S1A1 is more effective at stabilizing the S state (probably the force-generating state) of actomyosin, while S1A2 tends to stabilize the weak-binding (non-force-generating) W state. When a mixture of isoenzymes is present, S1A1 is dominant in its effects on actin dynamics. We conclude that ELC of skeletal muscle myosin modulates strong-to-weak structural transitions during the actomyosin ATPase cycle in an isoform-dependent manner, with significant implications for the contractile function of actomyosin.
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Affiliation(s)
- Ewa Prochniewicz
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
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11
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Jain T, Sheehan P, Crum J, Carragher B, Potter CS. Spotiton: a prototype for an integrated inkjet dispense and vitrification system for cryo-TEM. J Struct Biol 2012; 179:68-75. [PMID: 22569522 PMCID: PMC3378829 DOI: 10.1016/j.jsb.2012.04.020] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2012] [Revised: 04/19/2012] [Accepted: 04/25/2012] [Indexed: 01/29/2023]
Abstract
Over the last three decades, Cryo-TEM has developed into a powerful technique for high-resolution imaging of biological macromolecules in their native vitrified state. However, the method for vitrifying specimens onto EM grids is essentially unchanged - application of ∼3 μL sample to a grid, followed by blotting and rapid plunge freezing into liquid ethane. Several trials are often required to obtain suitable thin (few hundred nanometers or less) vitrified layers amenable for cryo-TEM imaging, which results in waste of precious sample and resources. While commercially available instruments provide some level of automation to control the vitrification process in an effort to increase quality and reproducibility, obtaining satisfactory vitrified specimens remains a bottleneck in the Cryo-TEM pipeline. We describe here a completely novel method for EM specimen preparation based on small volume (picoliter to nanoliter) dispensing using inkjet technology. A first prototype system (Spotiton v0.5) demonstrates feasibility of this new approach for specimen vitrification. A piezo-electric inkjet dispenser is integrated with optical real-time cameras (100 Hz frame rate) to analyze picoliter to nanoliter droplet profiles in-flight and spreading dynamics on the grid, and thus provides a method to optimize timing of the process. Using TEM imaging and biochemical assays we demonstrate that the piezo-electric inkjet mechanism does not disrupt the structural or functional integrity of macromolecules. These preliminary studies provide insight into the factors and components that will need further development to enable a robust and repeatable technique for specimen vitrification using this novel approach.
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Affiliation(s)
- Tilak Jain
- The National Resource for Automated Molecular Microscopy, Department of Cell Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
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12
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Okazaki KI, Sato T, Takano M. Temperature-enhanced association of proteins due to electrostatic interaction: a coarse-grained simulation of actin-myosin binding. J Am Chem Soc 2012; 134:8918-25. [PMID: 22559201 DOI: 10.1021/ja301447j] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Association of protein molecules constitutes the basis for the interaction network in a cell. Despite its fundamental importance, the thermodynamic aspect of protein-protein binding, particularly the issues relating to the entropy change upon binding, remains elusive. The binding of actin and myosin, which are vital proteins in motility, is a typical example, in which two different binding mechanisms have been argued: the binding affinity increases with increasing temperature and with decreasing salt-concentration, indicating the entropy-driven binding and the enthalpy-driven binding, respectively. How can these thermodynamically different binding mechanisms coexist? To address this question, which is of general importance in understanding protein-protein bindings, we conducted an in silico titration of the actin-myosin system by molecular dynamics simulation using a residue-level coarse-grained model, with particular focus on the role of the electrostatic interaction. We found a good agreement between in silico and in vitro experiments on the salt-concentration dependence and the temperature dependence of the binding affinity. We then figured out how the two binding mechanisms can coexist: the enthalpy (due to electrostatic interaction between actin and myosin) provides the basal binding affinity, and the entropy (due to the orientational disorder of water molecules) enhances it at higher temperatures. In addition, we analyzed the actin-myosin complex structures observed during the simulation and obtained a variety of weak-binding complex structures, among which were found an unusual binding mode suggested by an earlier experiment and precursor structures of the strong-binding complex proposed by electron microscopy. These results collectively indicate the potential capability of a residue-level coarse-grained model to simulate the association-dissociation dynamics (particularly for transient weak-bindings) exhibited by larger and more complicated systems, as in a cell.
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Affiliation(s)
- Kei-ichi Okazaki
- Department of Pure and Applied Physics, Waseda University, 3-4-1 Okubo, Shinjuku-Ku, Tokyo, Japan
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13
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Wu S, Liu J, Reedy MC, Tregear RT, Winkler H, Franzini-Armstrong C, Sasaki H, Lucaveche C, Goldman YE, Reedy MK, Taylor KA. Electron tomography of cryofixed, isometrically contracting insect flight muscle reveals novel actin-myosin interactions. PLoS One 2010; 5. [PMID: 20844746 PMCID: PMC2936580 DOI: 10.1371/journal.pone.0012643] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2010] [Accepted: 07/29/2010] [Indexed: 11/18/2022] Open
Abstract
Background Isometric muscle contraction, where force is generated without muscle shortening, is a molecular traffic jam in which the number of actin-attached motors is maximized and all states of motor action are trapped with consequently high heterogeneity. This heterogeneity is a major limitation to deciphering myosin conformational changes in situ. Methodology We used multivariate data analysis to group repeat segments in electron tomograms of isometrically contracting insect flight muscle, mechanically monitored, rapidly frozen, freeze substituted, and thin sectioned. Improved resolution reveals the helical arrangement of F-actin subunits in the thin filament enabling an atomic model to be built into the thin filament density independent of the myosin. Actin-myosin attachments can now be assigned as weak or strong by their motor domain orientation relative to actin. Myosin attachments were quantified everywhere along the thin filament including troponin. Strong binding myosin attachments are found on only four F-actin subunits, the “target zone”, situated exactly midway between successive troponin complexes. They show an axial lever arm range of 77°/12.9 nm. The lever arm azimuthal range of strong binding attachments has a highly skewed, 127° range compared with X-ray crystallographic structures. Two types of weak actin attachments are described. One type, found exclusively in the target zone, appears to represent pre-working-stroke intermediates. The other, which contacts tropomyosin rather than actin, is positioned M-ward of the target zone, i.e. the position toward which thin filaments slide during shortening. Conclusion We present a model for the weak to strong transition in the myosin ATPase cycle that incorporates azimuthal movements of the motor domain on actin. Stress/strain in the S2 domain may explain azimuthal lever arm changes in the strong binding attachments. The results support previous conclusions that the weak attachments preceding force generation are very different from strong binding attachments.
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Affiliation(s)
- Shenping Wu
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida, United States of America
| | - Jun Liu
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida, United States of America
| | - Mary C. Reedy
- Department of Cell Biology, Duke University Medical Center, Durham, North Carolina, United States of America
| | - Richard T. Tregear
- Medical Research Council Laboratory of Molecular Biology, Cambridge, England
| | - Hanspeter Winkler
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida, United States of America
| | - Clara Franzini-Armstrong
- Pennsylvania Muscle Institute, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Hiroyuki Sasaki
- Division of Fine Morphology, Core Research Facilities, Jikei University School of Medicine, Tokyo, Japan
| | - Carmen Lucaveche
- Department of Cell Biology, Duke University Medical Center, Durham, North Carolina, United States of America
| | - Yale E. Goldman
- Pennsylvania Muscle Institute, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Michael K. Reedy
- Department of Cell Biology, Duke University Medical Center, Durham, North Carolina, United States of America
| | - Kenneth A. Taylor
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida, United States of America
- * E-mail:
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14
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Unidirectional Brownian motion observed in an in silico single molecule experiment of an actomyosin motor. Proc Natl Acad Sci U S A 2010; 107:7769-74. [PMID: 20385833 DOI: 10.1073/pnas.0911830107] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The actomyosin molecular motor, the motor composed of myosin II and actin filament, is responsible for muscle contraction, converting chemical energy into mechanical work. Although recent single molecule and structural studies have shed new light on the energy-converting mechanism, the physical basis of the molecular-level mechanism remains unclear because of the experimental limitations. To provide a clue to resolve the controversy between the lever-arm mechanism and the Brownian ratchet-like mechanism, we here report an in silico single molecule experiment of an actomyosin motor. When we placed myosin on an actin filament and allowed myosin to move along the filament, we found that myosin exhibits a unidirectional Brownian motion along the filament. This unidirectionality was found to arise from the combination of a nonequilibrium condition realized by coupling to the ATP hydrolysis and a ratchet-like energy landscape inherent in the actin-myosin interaction along the filament, indicating that a Brownian ratchet-like mechanism contributes substantially to the energy conversion of this molecular motor.
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15
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Lyumkis D, Moeller A, Cheng A, Herold A, Hou E, Irving C, Jacovetty EL, Lau PW, Mulder AM, Pulokas J, Quispe JD, Voss NR, Potter CS, Carragher B. Automation in single-particle electron microscopy connecting the pieces. Methods Enzymol 2010; 483:291-338. [PMID: 20888480 DOI: 10.1016/s0076-6879(10)83015-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Throughout the history of single-particle electron microscopy (EM), automated technologies have seen varying degrees of emphasis and development, usually depending upon the contemporary demands of the field. We are currently faced with increasingly sophisticated devices for specimen preparation, vast increases in the size of collected data sets, comprehensive algorithms for image processing, sophisticated tools for quality assessment, and an influx of interested scientists from outside the field who might lack the skills of experienced microscopists. This situation places automated techniques in high demand. In this chapter, we provide a generic definition of and discuss some of the most important advances in automated approaches to specimen preparation, grid handling, robotic screening, microscope calibrations, data acquisition, image processing, and computational infrastructure. Each section describes the general problem and then provides examples of how that problem has been addressed through automation, highlighting available processing packages, and sometimes describing the particular approach at the National Resource for Automated Molecular Microscopy (NRAMM). We contrast the more familiar manual procedures with automated approaches, emphasizing breakthroughs as well as current limitations. Finally, we speculate on future directions and improvements in automated technologies. Our overall goal is to present automation as more than simply a tool to save time. Rather, we aim to illustrate that automation is a comprehensive and versatile strategy that can deliver biological information on an unprecedented scale beyond the scope available with classical manual approaches.
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Affiliation(s)
- Dmitry Lyumkis
- National Resource for Automated Molecular Microscopy, Department of Cell Biology, The Scripps Research Institute, La Jolla, California, USA
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16
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Koubassova NA, Bershitsky SY, Tsaturyan AK. A mathematical model of mechanical responses of contracting muscle fibers to temperature jumps. Biophysics (Nagoya-shi) 2009. [DOI: 10.1134/s0006350909040204] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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17
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Nabiev SR, Ovsyannikov DA, Bershitsky BY, Bershitsky SY. Optical trap as a tool for studying motor proteins. Biophysics (Nagoya-shi) 2009. [DOI: 10.1134/s0006350908060031] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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18
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Characterization of the pre-force-generation state in the actomyosin cross-bridge cycle. Proc Natl Acad Sci U S A 2008; 105:8631-6. [PMID: 18552179 DOI: 10.1073/pnas.0710793105] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Myosin is an actin-based motor protein that generates force by cycling between actin-attached (strong binding: ADP or rigor) and actin-detached (weak binding: ATP or ADP.P(i)) states during its ATPase cycle. However, it remains unclear what specific conformational changes in the actin binding site take place on binding to actin, and how these structural changes lead to product release and the production of force and motion. We studied the dynamics of the actin binding region of myosin V by using fluorescence resonance energy transfer (FRET) to monitor conformational changes in the upper-50-kDa domain of the actin binding cleft in the weak and strong actin binding states. Steady-state and lifetime data monitoring the FRET signal suggest that the cleft is in a more open conformation in the weak actin binding states. Transient kinetic experiments suggest that a rapid conformational change occurs, which is consistent with cleft closure before actin-activated phosphate release. Our results have identified a pre-force-generation actomyosin ADP.P(i) state, and suggest force generation may occur from a state not yet seen by crystallography in which the actin binding cleft and the nucleotide binding pocket are closed. Computational modeling uncovers dramatic changes in the rigidity of the upper-50-kDa domain in different nucleotide states, which suggests that the intrinsic flexibility of this domain allows myosin motors to accomplish simultaneous tight nucleotide binding (closed nucleotide binding pocket) and high-affinity actin binding (closed actin binding cleft).
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19
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Plattner H, Hentschel J. Sub-second cellular dynamics: time-resolved electron microscopy and functional correlation. INTERNATIONAL REVIEW OF CYTOLOGY 2006; 255:133-76. [PMID: 17178466 DOI: 10.1016/s0074-7696(06)55003-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Subcellular processes, from molecular events to organellar responses and cell movement, cover a broad scale in time and space. Clearly the extremes, such as ion channel activation are accessible only by electrophysiology, whereas numerous routine methods exist for relatively slow processes. However, many other processes, from a millisecond time scale on, can be "caught" only by methods providing appropriate time resolution. Fast freezing (cryofixation) is the method of choice in that case. In combination with follow-up methodologies appropriate for electron microscopic (EM) analysis, with all its variations, such technologies can also provide high spatial resolution. Such analyses may include, for example, freeze-fracturing for analyzing restructuring of membrane components, scanning EM and other standard EM techniques, as well as analytical EM analyses. The latter encompass energy-dispersive x-ray microanalysis and electron spectroscopic imaging, all applicable, for instance, to the second messenger, calcium. Most importantly, when conducted in parallel, such analyses can provide a structural background to the functional analyses, such as cyclic nucleotide formation or protein de- or rephosphorylation during cell stimulation. In sum, we discuss many examples of how it is practically possible to achieve strict function-structure correlations in the sub-second time range. We complement this review by discussing alternative methods currently available to analyze fast cellular phenomena occurring in the sub-second time range.
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Affiliation(s)
- Helmut Plattner
- Department of Biology, University of Konstanz, 78457 Konstanz, Germany
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20
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Xie P, Dou SX, Wang PY. Model for kinetics of myosin-V molecular motors. Biophys Chem 2005; 120:225-36. [PMID: 16386350 DOI: 10.1016/j.bpc.2005.11.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2005] [Revised: 11/22/2005] [Accepted: 11/22/2005] [Indexed: 10/25/2022]
Abstract
A hand-over-hand model is presented for the processive movement of myosin-V based on previous biochemical experimental results and structural observations of nucleotide-dependent conformational changes of single-headed myosins. The model shows that the ADP-release rate of the trailing head is much higher than that of the leading head, thus giving a 1:1 mechanochemical coupling for the processive movement of the motor. It explains well the previous finding that some 36-nm steps consist of two substeps, while other 36-nm steps consist of no substeps. Using the model, the calculated kinetic behaviors of myosin-V such as the main and intermediate dwell time distributions, the load dependence of the average main and intermediate dwell time and the load dependence of occurrence frequency of the intermediate state under various nucleotide conditions show good quantitative agreement with previous experimental results.
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Affiliation(s)
- Ping Xie
- Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China.
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21
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Tregear RT, Reedy MC, Goldman YE, Taylor KA, Winkler H, Franzini-Armstrong C, Sasaki H, Lucaveche C, Reedy MK. Cross-bridge number, position, and angle in target zones of cryofixed isometrically active insect flight muscle. Biophys J 2004; 86:3009-19. [PMID: 15111415 PMCID: PMC1304167 DOI: 10.1016/s0006-3495(04)74350-7] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Electron micrographic tomograms of isometrically active insect flight muscle, freeze substituted after rapid freezing, show binding of single myosin heads at varying angles that is largely restricted to actin target zones every 38.7 nm. To quantify the parameters that govern this pattern, we measured the number and position of attached myosin heads by tracing cross-bridges through the three-dimensional tomogram from their origins on 14.5-nm-spaced shelves along the thick filament to their thin filament attachments in the target zones. The relationship between the probability of cross-bridge formation and axial offset between the shelf and target zone center was well fitted by a Gaussian distribution. One head of each myosin whose origin is close to an actin target zone forms a cross-bridge most of the time. The probability of cross-bridge formation remains high for myosin heads originating within 8 nm axially of the target zone center and is low outside 12 nm. We infer that most target zone cross-bridges are nearly perpendicular to the filaments (60% within 11 degrees ). The results suggest that in isometric contraction, most cross-bridges maintain tension near the beginning of their working stroke at angles near perpendicular to the filament axis. Moreover, in the absence of filament sliding, cross-bridges cannot change tilt angle while attached nor reach other target zones while detached, so may cycle repeatedly on and off the same actin target monomer.
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Affiliation(s)
- Richard T Tregear
- Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 2QH, United Kingdom.
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22
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Harrison M, Durose L, Song CF, Barratt E, Trinick J, Jones R, Findlay JBC. Structure and function of the vacuolar H+-ATPase: moving from low-resolution models to high-resolution structures. J Bioenerg Biomembr 2004; 35:337-45. [PMID: 14635779 DOI: 10.1023/a:1025728915565] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
In the absence of a high-resolution structure for the vacuolar H+-ATPase, a number of approaches can yield valuable information about structure/function relationships in the enzyme. Electron microscopy can provide not only a representation of the overall architecture of the complex, but also a low-resolution map onto which structures solved for individually expressed subunits can be fitted. Here we review the possibilities for electron microscopy of the Saccharomyces V-ATPase and examine the suitability of V-ATPase subunits for expression in high yield prokaryotic systems, a key step towards high-resolution structural studies. We also review the role of experimentally-derived structural models in understanding structure/function relationships in the V-ATPase, with particular reference to the complex of proton-translocating 16 kDa proteolipids in the membrane domain of the V-ATPase. This model in turn makes testable predictions about the sites of binding of bafilomycins and the functional interactions between the proteolipid and the single-copy membrane subunit Vph1p, with implications for the constitution of the proton translocation pathway.
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Affiliation(s)
- Michael Harrison
- School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom.
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23
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Burgess S, Walker M, Knight PJ, Sparrow J, Schmitz S, Offer G, Bullard B, Leonard K, Holt J, Trinick J. Structural Studies of Arthrin: Monoubiquitinated Actin. J Mol Biol 2004; 341:1161-73. [PMID: 15321713 DOI: 10.1016/j.jmb.2004.06.077] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2003] [Revised: 06/07/2004] [Accepted: 06/10/2004] [Indexed: 11/17/2022]
Abstract
Here, we report on the structure and in situ location of arthrin (monoubiquitinated actin). Labelling of insect muscle thin filaments with a ubiquitin antibody reveals that every seventh subunit along the filament long-pitch helices is ubiquitinated. A three-dimensional reconstruction of frozen-hydrated arthrin filaments was produced. This was based on a novel algorithm that divides filament images into short segments that are used for single-particle image processing. Difference maps with an actin filament reconstruction locate ubiquitin at the side of actin sub-domain 1 opposite where myosin binds. Consistent with the reconstructions, peptide mapping places the ubiquitin linkage on lysine 118 in actin. Molecular modelling was used to generate arthrin monomers from ubiquitin and actin crystal structures. Filament models constructed from these monomers were compared with the arthrin reconstruction. The reconstruction suggests ubiquitin attached to Lys118 adopts one or a few conformers, stabilized by a small interface with actin. The function of actin ubiquitination is not known, but may involve regulation of muscle contractile activity.
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Affiliation(s)
- Stan Burgess
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, UK
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24
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White HD, Thirumurugan K, Walker ML, Trinick J. A second generation apparatus for time-resolved electron cryo-microscopy using stepper motors and electrospray. J Struct Biol 2004; 144:246-52. [PMID: 14643227 DOI: 10.1016/j.jsb.2003.09.027] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We describe here a second generation apparatus for studying transient reaction conformations in macromolecules and their complexes by electron cryo-microscopy. Reactions are trapped by rapid freezing in times ranging from a few milliseconds to tens of seconds after initiation. Blotting of the electron microscope grid and freezing it in liquid ethane uses computer controlled microstepping motors. For the fastest time resolution, a blotted grid containing a thin film of one reactant is sprayed with small droplets containing a second reactant just before freezing. The spray is produced electrically (electrospray), which gives a dense cloud of droplets <1 microm in diameter from the 1-2 microl of solution required per grid. A second method in which two solutions are first mixed by turbulent flow and then blotted prior to freezing is used for reactions with time courses >1s.
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Affiliation(s)
- H D White
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23507, USA.
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25
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Nitao LK, Yeates TO, Reisler E. Conformational dynamics of the SH1-SH2 helix in the transition states of myosin subfragment-1. Biophys J 2002; 83:2733-41. [PMID: 12414706 PMCID: PMC1302358 DOI: 10.1016/s0006-3495(02)75283-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The alpha-helix containing the thiols, SH1 (Cys-707) and SH2 (Cys-697), has been proposed to be one of the structural elements responsible for the transduction of conformational changes in the myosin head (subfragment-1 (S1)). Previous studies, using a method that isolated and measured the rate of the SH1-SH2 cross-linking step, showed that this helix undergoes ligand-induced conformational changes. However, because of long incubation times required for the formation of the transition state complexes (S1.ADP.BeF(x), S1.ADP.AlF(4)-, and S1.ADP.V(i)), this method could not be used to determine the cross-linking rate constants for such states. In this study, kinetic data from the SH1-SH2 cross-linking reaction were analyzed by computational methods to extract rate constants for the two-step mechanism. For S1.ADP.BeF(x), the results obtained were similar to those for S1.ATPgammaS. For reactions involving S1.ADP.AlF(4)- and S1.ADP.V(i), the first step (SH1 modification) is rate limiting; consequently, only lower limits could be established for the rate constants of the cross-linking step. Nevertheless, these results show that the cross-linking rate constants in the transition state complexes are increased at least 20-fold for all the reagents, including the shortest one, compared with nucleotide-free S1. Thus, the SH1-SH2 helix appears to be destabilized in the post-hydrolysis state.
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Affiliation(s)
- Lisa K Nitao
- Department of Chemistry and Biochemistry, Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA
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26
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Terada TP, Sasai M, Yomo T. Conformational change of the actomyosin complex drives the multiple stepping movement. Proc Natl Acad Sci U S A 2002; 99:9202-6. [PMID: 12082180 PMCID: PMC123118 DOI: 10.1073/pnas.132711799] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Actin-myosin (actomyosin) generates mechanical force by consuming ATP molecules. We apply the energy landscape perspective to address a controversial issue as to whether the myosin head moves with multiple steps after a single ATP hydrolysis or only a single mechanical event of the lever-arm swinging follows a single ATP hydrolysis. Here we propose a theoretical model in which the refolding of the partially unfolded actomyosin complex and the movement of the myosin head along the actin filament are coupled. A single ATP hydrolysis is followed by the formation of a high free-energy partially unfolded actomyosin complex, which then gradually refolds with a concomitant multiple stepping movement on the way to the lowest free-energy rigor state. The model quantitatively explains the single-molecular observation of the multiple stepping movement and is consistent with structural observations of the disorder in the actomyosin-binding process. The model also explains the observed variety in dwell time before each step, which is not accounted for by previous models, such as the lever-arm or ratchet models.
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Affiliation(s)
- Tomoki P Terada
- Graduate School of Human Informatics, Nagoya University, Nagoya 464-8601, Japan.
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27
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Baker JE, Brosseau C, Joel PB, Warshaw DM. The biochemical kinetics underlying actin movement generated by one and many skeletal muscle myosin molecules. Biophys J 2002; 82:2134-47. [PMID: 11916869 PMCID: PMC1302007 DOI: 10.1016/s0006-3495(02)75560-4] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
To better understand how skeletal muscle myosin molecules move actin filaments, we determine the motion-generating biochemistry of a single myosin molecule and study how it scales with the motion-generating biochemistry of an ensemble of myosin molecules. First, by measuring the effects of various ligands (ATP, ADP, and P(i)) on event lifetimes, tau(on), in a laser trap, we determine the biochemical kinetics underlying the stepwise movement of an actin filament generated by a single myosin molecule. Next, by measuring the effects of these same ligands on actin velocities, V, in an in vitro motility assay, we determine the biochemistry underlying the continuous movement of an actin filament generated by an ensemble of myosin molecules. The observed effects of P(i) on single molecule mechanochemistry indicate that motion generation by a single myosin molecule is closely associated with actin-induced P(i) dissociation. We obtain additional evidence for this relationship by measuring changes in single molecule mechanochemistry caused by a smooth muscle HMM mutation that results in a reduced P(i)-release rate. In contrast, we observe that motion generation by an ensemble of myosin molecules is limited by ATP-induced actin dissociation (i.e., V varies as 1/tau(on)) at low [ATP], but deviates from this relationship at high [ATP]. The single-molecule data uniquely provide a direct measure of the fundamental mechanochemistry of the actomyosin ATPase reaction under a minimal load and serve as a clear basis for a model of ensemble motility in which actin-attached myosin molecules impose a load.
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Affiliation(s)
- Josh E Baker
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont 05405, USA
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28
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Craig R, Lehman W. Crossbridge and tropomyosin positions observed in native, interacting thick and thin filaments. J Mol Biol 2001; 311:1027-36. [PMID: 11531337 DOI: 10.1006/jmbi.2001.4897] [Citation(s) in RCA: 112] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Tropomyosin movements on thin filaments are thought to sterically regulate muscle contraction, but have not been visualized during active filament sliding. In addition, although 3-D visualization of myosin crossbridges has been possible in rigor, it has been difficult for thick filaments actively interacting with thin filaments. In the current study, using three-dimensional reconstruction of electron micrographs of interacting filaments, we have been able to resolve not only tropomyosin, but also the docking sites for weak and strongly bound crossbridges on thin filaments. In relaxing conditions, tropomyosin was observed on the outer domain of actin, and thin filament interactions with thick filaments were rare. In contracting conditions, tropomyosin had moved to the inner domain of actin, and extra density, reflecting weakly bound, cycling myosin heads, was also detected, on the extreme periphery of actin. In rigor conditions, tropomyosin had moved further on to the inner domain of actin, and strongly bound myosin heads were now observed over the junction of the inner and outer domains. We conclude (1) that tropomyosin movements consistent with the steric model of muscle contraction occur in interacting thick and thin filaments, (2) that myosin-induced movement of tropomyosin in activated filaments requires strongly bound crossbridges, and (3) that crossbridges are bound to the periphery of actin, at a site distinct from the strong myosin binding site, at an early stage of the crossbridge cycle.
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Affiliation(s)
- R Craig
- Department of Cell Biology, University of Massachusetts Medical School, Worcester, MA 01655, USA.
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29
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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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30
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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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31
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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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32
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Molloy JE, Kendrick-Jones J, Veigel C, Tregear RT. An unexpectedly large working stroke from chymotryptic fragments of myosin II. FEBS Lett 2000; 480:293-7. [PMID: 11034347 DOI: 10.1016/s0014-5793(00)01937-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Recent structural evidence indicates that the light chain domain of the myosin head (LCD) bends on the motor domain (MD) to move actin. Structural models usually assume that the actin-MD interface remains static and the possibility that part of the myosin working stroke might be produced by rotation about the acto-myosin interface has been neglected. We have used an optical trap to measure the movement produced by proteolytically shortened single rabbit skeletal muscle myosin heads (S-1(A1) and S-1(A2)). The working stroke produced by these shortened heads was more than that which the MD-LCD bend mechanism predicts from the full-length (papain) S-1's working stroke obtained under similar conditions. This result indicates that part of the working stroke may be caused by motor action at the actin-MD interface.
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Affiliation(s)
- J E Molloy
- Department of Biology, University of York, UK
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33
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Nitao LK, Reisler E. Actin and temperature effects on the cross-linking of the SH1-SH2 helix in myosin subfragment 1. Biophys J 2000; 78:3072-80. [PMID: 10827984 PMCID: PMC1300889 DOI: 10.1016/s0006-3495(00)76844-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
Past biochemical work on myosin subfragment 1 (S1) has shown that the bent alpha-helix containing the reactive thiols SH1 (Cys(707)) and SH2 (Cys(697)) changes upon nucleotide and actin binding. In this study, we investigated the conformational dynamics of the SH1-SH2 helix in two actin-bound states of myosin and examined the effect of temperature on this helix, using five cross-linking reagents that are 5-15 A in length. Actin inhibited the cross-linking of SH1 to SH2 on both S1 and S1.MgADP for all of the reagents. Because the rate of SH2 modification was not altered by actin, the inhibition of cross-linking must result from a strong stabilization of the SH1-SH2 helix in the actin-bound states of S1. The dynamics of the helix is also influenced by temperature. At 25 degrees C, the rate constants for cross-linking in S1 alone are low, with values of approximately 0.010 min(-1) for all of the reagents. At 4 degrees C, the rate constants, except for the shortest reagent, range between 0.030 and 0.070 min(-1). The rate constants for SH2 modification in SH1-modified S1 show the opposite trend; they increase with the increases in temperature. The greater cross-linking at the lower temperature indicates destabilization of the SH1-SH2 helix at 4 degrees C. These results are discussed in terms of conformational dynamics of the SH1-SH2 helix.
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Affiliation(s)
- L K Nitao
- Department of Chemistry and Biochemistry and the Molecular Biology Institute, University of California, Los Angeles 90095, USA
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34
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Abstract
The crystal structures of smooth muscle and scallop striated muscle myosin have both been completed in the past 18 months. Structural studies of unconventional myosins, in particular the stunning discovery that myosin VI moves backwards on actin, are starting to have deep impact on the field and have induced new ways of thinking about actin-based motility. Sophisticated genetic, biochemical and biophysical studies were used to test and refine hypotheses of the molecular mechanism of motility that were developed in the past. Although all these studies confirmed some aspects of these hypotheses, they also raised many new unresolved questions. Much of the evidence points to the importance of the actin-myosin binding process and an associated disorder-to-order transition.
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Affiliation(s)
- N Volkmann
- The Burnham Institute, La Jolla, 92037, USA.
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35
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Baker TS, Olson NH, Fuller SD. Adding the third dimension to virus life cycles: three-dimensional reconstruction of icosahedral viruses from cryo-electron micrographs. Microbiol Mol Biol Rev 1999; 63:862-922, table of contents. [PMID: 10585969 PMCID: PMC98980 DOI: 10.1128/mmbr.63.4.862-922.1999] [Citation(s) in RCA: 367] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Viruses are cellular parasites. The linkage between viral and host functions makes the study of a viral life cycle an important key to cellular functions. A deeper understanding of many aspects of viral life cycles has emerged from coordinated molecular and structural studies carried out with a wide range of viral pathogens. Structural studies of viruses by means of cryo-electron microscopy and three-dimensional image reconstruction methods have grown explosively in the last decade. Here we review the use of cryo-electron microscopy for the determination of the structures of a number of icosahedral viruses. These studies span more than 20 virus families. Representative examples illustrate the use of moderate- to low-resolution (7- to 35-A) structural analyses to illuminate functional aspects of viral life cycles including host recognition, viral attachment, entry, genome release, viral transcription, translation, proassembly, maturation, release, and transmission, as well as mechanisms of host defense. The success of cryo-electron microscopy in combination with three-dimensional image reconstruction for icosahedral viruses provides a firm foundation for future explorations of more-complex viral pathogens, including the vast number that are nonspherical or nonsymmetrical.
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Affiliation(s)
- T S Baker
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907-1392, USA.
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36
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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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37
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Conibear PB. Kinetic studies on the effects of ADP and ionic strength on the interaction between myosin subfragment-1 and actin: implications for load-sensitivity and regulation of the crossbridge cycle. J Muscle Res Cell Motil 1999; 20:727-42. [PMID: 10730576 DOI: 10.1023/a:1005696017544] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The dynamics of the interaction of fast skeletal muscle myosin subfragment-1 with pyrene-labelled actin were examined using both stopped-flow and pressure relaxation methods. The data suggest a four-step model i.e.: A + M.(N)(K0)<-->A approximately M.(N)(K1)<-->A - M.(N)(K2)<-->A.M.(N)(K3)<-->A.M.(N)#. ADP weakens the acto-S1 affinity via a reduction in Ko, with no apparent effect on K1 and no effect on K2, whilst k(+2) and k(-2) are both markedly reduced. Increased ionic strength reduces both K0 and k(+2) with no major effect on k(+1). Step 3 represents an extension to previous models and is ADP-dependent. The present work is discussed in relation to earlier studies which led to somewhat different conclusions (Taylor EW (1991) J Biol Chem 266: 294-302; Geeves MA (1989) Biochemistry 28: 5864-5871). It is likely that the interaction proceeds via formation of a disordered complex stabilised by ionic interactions (corresponding to step 0), followed by a disordered-to-ordered transition involving additional hydrophobic contacts (step 1) after which further contacts of both types are made coupled to internal conformational changes (steps 2 and 3). Step 3 could have a role in extending the lifetime of force-generating crossbridges and limiting ATP turnover during contraction against a load, and may be equivalent to a structural change observed in recent cryo-EM studies on the smooth muscle system (Whittaker M, Wilsonkubalek EM, Smith JE, Faust L, Milligan RA and Sweeney HL (1995) Nature 378: 748-751). Cooperative interactions between the two myosin heads also appear to have a role in this putative latch mechanism.
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Affiliation(s)
- P B Conibear
- Department of Biochemistry, University of Leicester, UK.
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