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Li J, Leung CWT, Wong DSH, Xu J, Li R, Zhao Y, Yung CYY, Zhao E, Tang BZ, Bian L. Photocontrolled SiRNA Delivery and Biomarker-Triggered Luminogens of Aggregation-Induced Emission by Up-Conversion NaYF 4:Yb 3+Tm 3+@SiO 2 Nanoparticles for Inducing and Monitoring Stem-Cell Differentiation. ACS APPLIED MATERIALS & INTERFACES 2019; 11:22074-22084. [PMID: 28350958 DOI: 10.1021/acsami.7b00845] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Controlling the differentiation of stem cells and monitoring cell differentiation has attracted much research interest since the discovery of stem cells. In this regard, a novel near-infrared (NIR) light-activated nanoplatform is obtained by encapsulating the photoactivatable caged compound (DMNPE/siRNA) and combining a MMP13 cleaved imaging peptide-tetrapheny-lethene (TPE) unit conjugated with the mesoporous silica-coated up-conversion nanoparticles (UCNPs) for the remote control of cell differentiation and, simultaneously, for the real-time monitoring of differentiation. Upon NIR light illumination, the photoactivated caged compound is activated, and the siRNA is released from UCNPs, allowing controlled differentiation of stem cells by light. More importantly, MMP13 enzyme triggered by osteogenic differentiation would effectively cleave the TPE probe peptide, thereby allowing the real-time monitoring of differentiation in living stem cells by aggregation-induced emission (AIE).
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Affiliation(s)
- Jinming Li
- Division of Biomedical Engineering , The Chinese University of Hong Kong , Hong Kong , China
| | - Chris Wai Tung Leung
- Department of Chemistry, Institute of Molecular Functional Materials , The Hong Kong University of Science and Technology (HKUST) , Kowloon, Hong Kong , China
| | - Dexter Siu Hong Wong
- Division of Biomedical Engineering , The Chinese University of Hong Kong , Hong Kong , China
| | - Jianbin Xu
- Division of Biomedical Engineering , The Chinese University of Hong Kong , Hong Kong , China
| | - Rui Li
- Division of Biomedical Engineering , The Chinese University of Hong Kong , Hong Kong , China
| | - Yueyue Zhao
- Department of Chemistry, Institute of Molecular Functional Materials , The Hong Kong University of Science and Technology (HKUST) , Kowloon, Hong Kong , China
| | - Chris Yu Yee Yung
- Department of Chemistry, Institute of Molecular Functional Materials , The Hong Kong University of Science and Technology (HKUST) , Kowloon, Hong Kong , China
| | - Engui Zhao
- Department of Chemistry, Institute of Molecular Functional Materials , The Hong Kong University of Science and Technology (HKUST) , Kowloon, Hong Kong , China
| | - Ben Zhong Tang
- Department of Chemistry, Institute of Molecular Functional Materials , The Hong Kong University of Science and Technology (HKUST) , Kowloon, Hong Kong , China
| | - Liming Bian
- Division of Biomedical Engineering , The Chinese University of Hong Kong , Hong Kong , China
- China Orthopedic Regenerative Medicine Group (CORMed) , Hangzhou , China
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Taylor KA, Rahmani H, Edwards RJ, Reedy MK. Insights into Actin-Myosin Interactions within Muscle from 3D Electron Microscopy. Int J Mol Sci 2019; 20:ijms20071703. [PMID: 30959804 PMCID: PMC6479483 DOI: 10.3390/ijms20071703] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2019] [Revised: 03/31/2019] [Accepted: 04/01/2019] [Indexed: 01/12/2023] Open
Abstract
Much has been learned about the interaction between myosin and actin through biochemistry, in vitro motility assays and cryo-electron microscopy (cryoEM) of F-actin, decorated with myosin heads. Comparatively less is known about actin-myosin interactions within the filament lattice of muscle, where myosin heads function as independent force generators and thus most measurements report an average signal from multiple biochemical and mechanical states. All of the 3D imaging by electron microscopy (EM) that has revealed the interplay of the regular array of actin subunits and myosin heads within the filament lattice has been accomplished using the flight muscle of the large water bug Lethocerus sp. The Lethocerus flight muscle possesses a particularly favorable filament arrangement that enables all the myosin cross-bridges contacting the actin filament to be visualized in a thin section. This review covers the history of this effort and the progress toward visualizing the complex set of conformational changes that myosin heads make when binding to actin in several static states, as well as the fast frozen actively contracting muscle. The efforts have revealed a consistent pattern of changes to the myosin head structures as determined by X-ray crystallography needed to explain the structure of the different actomyosin interactions observed in situ.
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Affiliation(s)
- Kenneth A Taylor
- Florida State University, Institute of Molecular Biophysics, Tallahassee, FL 32306-4380, USA.
| | - Hamidreza Rahmani
- Florida State University, Institute of Molecular Biophysics, Tallahassee, FL 32306-4380, USA.
| | - Robert J Edwards
- Duke University Medical Center, Department of Cell Biology, Durham, NC 27607, USA.
| | - Michael K Reedy
- Duke University Medical Center, Department of Cell Biology, Durham, NC 27607, USA.
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Synchrotron Radiation X-ray Diffraction Techniques Applied to Insect Flight Muscle. Int J Mol Sci 2018; 19:ijms19061748. [PMID: 29899245 PMCID: PMC6032142 DOI: 10.3390/ijms19061748] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Revised: 06/04/2018] [Accepted: 06/05/2018] [Indexed: 01/02/2023] Open
Abstract
X-ray fiber diffraction is a powerful tool used for investigating the molecular structure of muscle and its dynamics during contraction. This technique has been successfully applied not only to skeletal and cardiac muscles of vertebrates but also to insect flight muscle. Generally, insect flight muscle has a highly ordered structure and is often capable of high-frequency oscillations. The X-ray diffraction studies on muscle have been accelerated by the advent of 3rd-generation synchrotron radiation facilities, which can generate brilliant and highly oriented X-ray beams. This review focuses on some of the novel experiments done on insect flight muscle by using synchrotron radiation X-rays. These include diffraction recordings from single myofibrils within a flight muscle fiber by using X-ray microbeams and high-speed diffraction recordings from the flight muscle during the wing-beat of live insects. These experiments have provided information about the molecular structure and dynamic function of flight muscle in unprecedented detail. Future directions of X-ray diffraction studies on muscle are also discussed.
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Wu S, Liu J, Reedy MC, Perz-Edwards RJ, Tregear RT, Winkler H, Franzini-Armstrong C, Sasaki H, Lucaveche C, Goldman YE, Reedy MK, Taylor KA. Structural changes in isometrically contracting insect flight muscle trapped following a mechanical perturbation. PLoS One 2012; 7:e39422. [PMID: 22761792 PMCID: PMC3382574 DOI: 10.1371/journal.pone.0039422] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2012] [Accepted: 05/18/2012] [Indexed: 11/18/2022] Open
Abstract
The application of rapidly applied length steps to actively contracting muscle is a classic method for synchronizing the response of myosin cross-bridges so that the average response of the ensemble can be measured. Alternatively, electron tomography (ET) is a technique that can report the structure of the individual members of the ensemble. We probed the structure of active myosin motors (cross-bridges) by applying 0.5% changes in length (either a stretch or a release) within 2 ms to isometrically contracting insect flight muscle (IFM) fibers followed after 5–6 ms by rapid freezing against a liquid helium cooled copper mirror. ET of freeze-substituted fibers, embedded and thin-sectioned, provides 3-D cross-bridge images, sorted by multivariate data analysis into ∼40 classes, distinct in average structure, population size and lattice distribution. Individual actin subunits are resolved facilitating quasi-atomic modeling of each class average to determine its binding strength (weak or strong) to actin. ∼98% of strong-binding acto-myosin attachments present after a length perturbation are confined to “target zones” of only two actin subunits located exactly midway between successive troponin complexes along each long-pitch helical repeat of actin. Significant changes in the types, distribution and structure of actin-myosin attachments occurred in a manner consistent with the mechanical transients. Most dramatic is near disappearance, after either length perturbation, of a class of weak-binding cross-bridges, attached within the target zone, that are highly likely to be precursors of strong-binding cross-bridges. These weak-binding cross-bridges were originally observed in isometrically contracting IFM. Their disappearance following a quick stretch or release can be explained by a recent kinetic model for muscle contraction, as behaviour consistent with their identification as precursors of strong-binding cross-bridges. The results provide a detailed model for contraction in IFM that may be applicable to contraction in other types of muscle.
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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
| | - Robert J. Perz-Edwards
- 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, United Kingdom
| | - 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
- Institute of DNA Medicine, 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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Craig R. Isolation, electron microscopy and 3D reconstruction of invertebrate muscle myofilaments. Methods 2011; 56:33-43. [PMID: 22155190 DOI: 10.1016/j.ymeth.2011.11.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2011] [Revised: 11/22/2011] [Accepted: 11/26/2011] [Indexed: 10/14/2022] Open
Abstract
Understanding the molecular mechanism of muscle contraction and its regulation has been greatly influenced and aided by studies of myofilament structure in invertebrate muscles. Invertebrates are easily obtained and cover a broad spectrum of species and functional specializations. The thick (myosin-containing) filaments from some invertebrates are especially stable and simple in structure and thus much more amenable to structural analysis than those of vertebrates. Comparative studies of invertebrate filaments by electron microscopy and image processing have provided important generalizations of muscle molecular structure and function. This article reviews methods for preparing thick and thin filaments from invertebrate muscle, for imaging filaments by electron microscopy, and for determining their three dimensional structure by image processing. It also highlights some of the key insights into filament function that have come from these studies.
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Affiliation(s)
- Roger Craig
- Department of Cell Biology, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, MA 01655, USA.
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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: 54] [Impact Index Per Article: 3.9] [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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7
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Wu S, Liu J, Reedy MC, Winkler H, Reedy MK, Taylor KA. Methods for identifying and averaging variable molecular conformations in tomograms of actively contracting insect flight muscle. J Struct Biol 2009; 168:485-502. [PMID: 19698791 PMCID: PMC2805068 DOI: 10.1016/j.jsb.2009.08.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2009] [Revised: 08/12/2009] [Accepted: 08/15/2009] [Indexed: 11/26/2022]
Abstract
During active muscle contraction, tension is generated through many simultaneous, independent interactions between the molecular motor myosin and the actin filaments. The ensemble of myosin motors displays heterogeneous conformations reflecting different mechanochemical steps of the ATPase pathway. We used electron tomography of actively contracting insect flight muscle fast-frozen, freeze substituted, Araldite embedded, thin-sectioned and stained, to obtain 3D snapshots of the multiplicity of actin-attached myosin structures. We describe procedures for alignment of the repeating lattice of sub-volumes (38.7 nm cross-bridge repeats bounded by troponin) and multivariate data analysis to identify self-similar repeats for computing class averages. Improvements in alignment and classification of repeat sub-volumes reveals (for the first time in active muscle images) the helix of actin subunits in the thin filament and the troponin density with sufficient clarity that a quasiatomic model of the thin filament can be built into the class averages independent of the myosin cross-bridges. We show how quasiatomic model building can identify both strong and weak myosin attachments to actin. We evaluate the accuracy of image classification to enumerate the different types of actin-myosin attachments.
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Affiliation(s)
- Shenping Wu
- Institute of Molecular Biophysics, Florida State University, Florida 32306-4380, USA
| | - Jun Liu
- Institute of Molecular Biophysics, Florida State University, Florida 32306-4380, USA
| | - Mary C. Reedy
- Dept of Cell Biology, Duke University Medical Center, Durham, NC 27710 USA
| | - Hanspeter Winkler
- Institute of Molecular Biophysics, Florida State University, Florida 32306-4380, USA
| | - Michael K. Reedy
- Dept of Cell Biology, Duke University Medical Center, Durham, NC 27710 USA
| | - Kenneth A. Taylor
- Institute of Molecular Biophysics, Florida State University, Florida 32306-4380, USA
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Tikunov BA, Rome LC. Controlling the freezing process: A robotic device for rapidly freezing biological tissues with millisecond time resolution. Cryobiology 2007; 55:93-7. [PMID: 17640628 DOI: 10.1016/j.cryobiol.2007.06.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2007] [Revised: 06/01/2007] [Accepted: 06/04/2007] [Indexed: 11/20/2022]
Abstract
A robotic cryogenic device was developed which allows freezing of thick biological tissues with millisecond time resolution. The device consists of two horizontally oriented hammers (pre-cooled with liquid N(2)) driven by two linear servo-motors. The tissue sample is bathed in Ringers contained in a chamber which drops rapidly out of the way just as the hammers approach. A third linear motor is vertically oriented, and permits the rapidly dropping chamber to smoothly decelerate. All movements were performed by the three motors and four solenoids controlled by a PC. Mechanical adjustments, that change the size of the gap between the hammers at the end position, permit the final thickness of the frozen tissue to be varied. Here we show that the freezing time increased with the square of the final thickness of the frozen bundle. However, when bundles of different original thicknesses (up to at least 1mm) were compressed to the same final thickness (e.g., 0.2mm), they exhibited nearly equal freezing times. Hence, by being able to adjust the final thickness of the frozen bundles, the device not only speeds the rate of freezing, but standardizes the freezing time for different diameter samples. This permits the use of freezing for accurate determination of the kinetics of cellular processes in biological tissue.
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Affiliation(s)
- Boris A Tikunov
- Biology Department, University of Pennsylvania, Philadelphia, PA 19087, USA
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9
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Affiliation(s)
- Kenneth A Taylor
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306, USA
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10
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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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11
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Liu J, Reedy MC, Goldman YE, Franzini-Armstrong C, Sasaki H, Tregear RT, Lucaveche C, Winkler H, Baumann BAJ, Squire JM, Irving TC, Reedy MK, Taylor KA. Electron tomography of fast frozen, stretched rigor fibers reveals elastic distortions in the myosin crossbridges. J Struct Biol 2005; 147:268-82. [PMID: 15450296 DOI: 10.1016/j.jsb.2004.03.008] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2003] [Revised: 03/19/2004] [Indexed: 11/16/2022]
Abstract
As a first step toward freeze-trapping and 3-D modeling of the very rapid load-induced structural responses of active myosin heads, we explored the conformational range of longer lasting force-dependent changes in rigor crossbridges of insect flight muscle (IFM). Rigor IFM fibers were slam-frozen after ramp stretch (1000 ms) of 1-2% and freeze-substituted. Tomograms were calculated from tilt series of 30 nm longitudinal sections of Araldite-embedded fibers. Modified procedures of alignment and correspondence analysis grouped self-similar crossbridge forms into 16 class averages with 4.5 nm resolution, revealing actin protomers and myosin S2 segments of some crossbridges for the first time in muscle thin sections. Acto-S1 atomic models manually fitted to crossbridge density required a range of lever arm adjustments to match variably distorted rigor crossbridges. Some lever arms were unchanged compared with low tension rigor, while others were bent and displaced M-ward by up to 4.5 nm. The average displacement was 1.6 +/- 1.0 nm. "Map back" images that replaced each unaveraged 39 nm crossbridge motif by its class average showed an ordered mix of distorted and unaltered crossbridges distributed along the 116 nm repeat that reflects differences in rigor myosin head loading even before stretch.
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Affiliation(s)
- Jun Liu
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306-4380, USA
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12
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Ferenczi MA, Bershitsky SY, Koubassova N, Siththanandan V, Helsby WI, Panine P, Roessle M, Narayanan T, Tsaturyan AK. The “Roll and Lock” Mechanism of Force Generation in Muscle. Structure 2005; 13:131-41. [PMID: 15642268 DOI: 10.1016/j.str.2004.11.007] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2004] [Revised: 11/05/2004] [Accepted: 11/05/2004] [Indexed: 11/23/2022]
Abstract
Muscle force results from the interaction of the globular heads of myosin-II with actin filaments. We studied the structure-function relationship in the myosin motor in contracting muscle fibers by using temperature jumps or length steps combined with time-resolved, low-angle X-ray diffraction. Both perturbations induced simultaneous changes in the active muscle force and in the extent of labeling of the actin helix by stereo-specifically bound myosin heads at a constant total number of attached heads. The generally accepted hypothesis assumes that muscle force is generated solely by tilting of the lever arm, or the light chain domain of the myosin head, about its catalytic domain firmly bound to actin. Data obtained suggest an additional force-generating step: the "roll and lock" transition of catalytic domains of non-stereo-specifically attached heads to a stereo-specifically bound state. A model based on this scheme is described to quantitatively explain the data.
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13
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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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14
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Yamada T, Takezawa Y, Iwamoto H, Suzuki S, Wakabayashi K. Rigor-force producing cross-bridges in skeletal muscle fibers activated by a substoichiometric amount of ATP. Biophys J 2003; 85:1741-53. [PMID: 12944289 PMCID: PMC1303348 DOI: 10.1016/s0006-3495(03)74604-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2002] [Accepted: 04/10/2003] [Indexed: 10/21/2022] Open
Abstract
Isometric skinned muscle fibers were activated by the photogeneration of a substoichiometric amount of ATP and their cross-bridge configurations examined during the development of the rigor force by x-ray diffraction and electron microscopy. By the photogeneration of approximately 100 microM ATP, approximately 2/3 of the concentration of the myosin heads in a muscle fiber, muscle fibers originally in the rigor state showed a transient drop of the force and then produced a long-lasting rigor force (approximately 50% of the maximal active force), which gradually recovered to the original force level with a time constant of approximately 4 s. Associated with the photoactivation, muscle fibers revealed small but distinct changes in the equatorial x-ray diffraction that run ahead of the development of force. After reaching a plateau of force, long-lasting intensity changes in the x-ray diffraction pattern developed in parallel with the force decline. Two-dimensional x-ray diffraction patterns and electron micrographs of the sectioned muscle fibers taken during the period of 1-1.9 s after the photoactivation were basically similar to those from rigor preparations but also contained features characteristic of fully activated fibers. In photoactivated muscle fibers, some cross-bridges bound photogenerated ATP and underwent an ATP hydrolysis cycle whereas a significant population of the cross-bridges remained attached to the thin actin filaments with no available ATP to bind. Analysis of the results obtained indicates that, during the ATP hydrolysis reaction, the cross-bridges detached from actin filaments and reattached either to the same original actin monomers or to neighboring actin monomers. The latter cross-bridges contribute to produce the rigor force by interacting with the actin filaments, first producing the active force and then being locked in a noncycling state(s), transforming their configuration on the actin filaments to stably sustain the produced force as a passive rigor force.
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Affiliation(s)
- Takenori Yamada
- Department of Physiology, School of Medicine, Teikyo University, Tokyo 173-8605, Japan.
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Abstract
Cryoelectron microscopy makes it possible to record high-resolution detail from large and complex structures. However, its application to understanding cellular structure is limited by the requirement that samples should be no thicker than approximately 0.5-1 microm. Therefore it is important to develop the ability to section biological material so that it can be imaged in its native frozen state. Here we have adapted standard methods of preparing cryosections so that they can be imaged by cryoelectron microscopy. As used for immunolabeling, cryosections of chemically fixed, cryoprotected frozen rat cardiac muscle were thawed, applied to carbon-coated grids, and rinsed on a drop of buffer. The special step here is that the cryosections were then refrozen by being plunged into liquid ethane and imaged at approximately -180 degrees C in a 200-kV field-emission gun electron microscope. The unstained cryosections have good contrast, allowing the identification of optimum regions of the sample. Considerable fine detail is observed within the substructure of the sarcomere A-band and I-band. Fourier transform analysis of the micrographs shows that this method preserves high structural order, hence these sections are well-suited to 3D reconstruction. We conclude that this approach has considerable potential for obtaining intermediate- and high-resolution structural detail from bulk tissue.
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Affiliation(s)
- Pradeep K Luther
- Biological Structure & Function Section, Biomedical Sciences Division, Faculty of Medicine, Imperial College, Exhibition Road, London SW7 2AZ, UK.
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16
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Affiliation(s)
- John M Murray
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Room 1045 BRB IIIII Building, 421 Curie Boulevard, Philadelphia, PA 19104-6058, USA
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17
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Bell MG, Dale RE, van der Heide UA, Goldman YE. Polarized fluorescence depletion reports orientation distribution and rotational dynamics of muscle cross-bridges. Biophys J 2002; 83:1050-73. [PMID: 12124286 PMCID: PMC1302208 DOI: 10.1016/s0006-3495(02)75230-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
The method of polarized fluorescence depletion (PFD) has been applied to enhance the resolution of orientational distributions and dynamics obtained from fluorescence polarization (FP) experiments on ordered systems, particularly in muscle fibers. Previous FP data from single fluorescent probes were limited to the 2(nd)- and 4(th)-rank order parameters, <P(2)(cos beta)> and <P(4)(cos beta)>, of the probe angular distribution (beta) relative to the fiber axis and <P(2d)>, a coefficient describing the extent of rapid probe motions. We applied intense 12-micros polarized photoselection pulses to transiently populate the triplet state of rhodamine probes and measured the polarization of the ground-state depletion using a weak interrogation beam. PFD provides dynamic information describing the extent of motions on the time scale between the fluorescence lifetime (e.g., 4 ns) and the duration of the photoselection pulse and it potentially supplies information about the probe angular distribution corresponding to order parameters above rank 4. Gizzard myosin regulatory light chain (RLC) was labeled with the 6-isomer of iodoacetamidotetramethylrhodamine and exchanged into rabbit psoas muscle fibers. In active contraction, dynamic motions of the RLC on the PFD time scale were intermediate between those observed in relaxation and rigor. The results indicate that previously observed disorder of the light chain region in contraction can be ascribed principally to dynamic motions on the microsecond time scale.
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Affiliation(s)
- Marcus G Bell
- Pennsylvania Muscle Institute, The School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6083, USA
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18
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Uyeda TQP, Tokuraku K, Kaseda K, Webb MR, Patterson B. Evidence for a novel, strongly bound acto-S1 complex carrying ADP and phosphate stabilized in the G680V mutant of Dictyostelium myosin II. Biochemistry 2002; 41:9525-34. [PMID: 12135375 DOI: 10.1021/bi026177i] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Gly 680 of Dictyostelium myosin II sits at a critical position within the reactive thiol helices. We have previously shown that G680V mutant subfragment 1 largely remains in strongly actin-bound states in the presence of ATP. We speculated that acto-G680V subfragment 1 complexes accumulate in the A.M.ADP.P(i) state on the basis of the biochemical phenotypes conferred by mutations which suppress the G680V mutation in vivo [Wu, Y., et al. (1999) Genetics 153, 107-116]. Here, we report further characterization of the interaction between actin and G680V subfragment 1. Light scattering data demonstrate that the majority of G680V subfragment 1 is bound to actin in the presence of ATP. These acto-G680V subfragment 1 complexes in the presence of ATP do not efficiently quench the fluorescence of pyrene-actin, unlike those in rigor complexes or in the presence of ADP alone. Kinetic analyses demonstrated that phosphate release, but not ATP hydrolysis or ADP release, is very slow and rate limiting in the acto-G680V subfragment 1 ATPase cycle. Single turnover kinetic analysis demonstrates that, during ATP hydrolysis by the acto-G680V subfragment 1 complex, quenching of pyrene fluorescence significantly lags the increase of light scattering. This is unlike the situation with wild-type subfragment 1, where the two signals have similar rate constants. These data support the hypothesis that the main intermediate during ATP hydrolysis by acto-G680V subfragment 1 is an acto-subfragment 1 complex carrying ADP and P(i), which scatters light but does not quench the pyrene fluorescence and so has a different conformation from the rigor complex.
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Affiliation(s)
- Taro Q P Uyeda
- Gene Discovery Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8562, Japan.
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19
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Hopkins SC, Sabido-David C, van der Heide UA, Ferguson RE, Brandmeier BD, Dale RE, Kendrick-Jones J, Corrie JET, Trentham DR, Irving M, Goldman YE. Orientation changes of the myosin light chain domain during filament sliding in active and rigor muscle. J Mol Biol 2002; 318:1275-91. [PMID: 12083517 DOI: 10.1016/s0022-2836(02)00189-4] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Structural changes in myosin power many types of cell motility including muscle contraction. Tilting of the myosin light chain domain (LCD) seems to be the final step in transducing the energy of ATP hydrolysis, amplifying small structural changes near the ATP binding site into nanometer-scale motions of the filaments. Here we used polarized fluorescence measurements from bifunctional rhodamine probes attached at known orientations in the LCD to describe the distribution of orientations of the LCD in active contraction and rigor. We applied rapid length steps to perturb the orientations of the population of myosin heads that are attached to actin, and thereby characterized the motions of these force-bearing myosin heads. During active contraction, this population is a small fraction of the total. When the filaments slide in the shortening direction in active contraction, the long axis of LCD tilts towards its nucleotide-free orientation with no significant twisting around this axis. In contrast, filament sliding in rigor produces coordinated tilting and twisting motions.
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Affiliation(s)
- Seth C Hopkins
- Pennsylvania Muscle Institute, University of Pennsylvania, Philadelphia 19104-6083, USA
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20
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Kraft T, Mattei T, Radocaj A, Piep B, Nocula C, Furch M, Brenner B. Structural features of cross-bridges in isometrically contracting skeletal muscle. Biophys J 2002; 82:2536-47. [PMID: 11964242 PMCID: PMC1302044 DOI: 10.1016/s0006-3495(02)75597-5] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
Two-dimensional x-ray diffraction was used to investigate structural features of cross-bridges that generate force in isometrically contracting skeletal muscle. Diffraction patterns were recorded from arrays of single, chemically skinned rabbit psoas muscle fibers during isometric force generation, under relaxation, and in rigor. In isometric contraction, a rather prominent intensification of the actin layer lines at 5.9 and 5.1 nm and of the first actin layer line at 37 nm was found compared with those under relaxing conditions. Surprisingly, during isometric contraction, the intensity profile of the 5.9-nm actin layer line was shifted toward the meridian, but the resulting intensity profile was different from that observed in rigor. We particularly addressed the question whether the differences seen between rigor and active contraction might be due to a rigor-like configuration of both myosin heads in the absence of nucleotide (rigor), whereas during active contraction only one head of each myosin molecule is in a rigor-like configuration and the second head is weakly bound. To investigate this question, we created different mixtures of weak binding myosin heads and rigor-like actomyosin complexes by titrating MgATPgammaS at saturating [Ca2+] into arrays of single muscle fibers. The resulting diffraction patterns were different in several respects from patterns recorded under isometric contraction, particularly in the intensity distribution along the 5.9-nm actin layer line. This result indicates that cross-bridges present during isometric force generation are not simply a mixture of weakly bound and single-headed rigor-like complexes but are rather distinctly different from the rigor-like cross-bridge. Experiments with myosin-S1 and truncated S1 (motor domain) support the idea that for a force generating cross-bridge, disorder due to elastic distortion might involve a larger part of the myosin head than for a nucleotide free, rigor cross-bridge.
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Affiliation(s)
- Theresia Kraft
- Molecular and Cellular Physiology, Medical School, D-30625 Hannover, Germany.
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21
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Stegmann H, Fink RH. A combined solution exchange/plunge-freezing device for skinned muscle fibers. J Muscle Res Cell Motil 1999; 20:497-503. [PMID: 10555068 DOI: 10.1023/a:1005527328882] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
For many contractility studies, defined functional states of skinned muscle fiber preparations can be introduced by application of standardized perfusion protocols with large varieties of experimental solutions. Functionally important subcellular element distributions in the myoplasm and in the sarcoplasmic reticulum can be measured with high spatial resolution by electron microscopic microanalysis. Capturing these subcellular ion distributions requires their rapid immobilization by quick-freezing. We therefore combined a plunge-freezing device with a semiautomatic solution exchanger to reproducibly perfuse skinned muscle fiber bundles with multiple solutions. The isometric tension produced is simultaneously recorded as an indicator for the functional state. The samples can be quick-frozen at any chosen time of the tension transient. A cryoglueing technique finally delivers specimens suitable for cryoultramicrotomy.
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Affiliation(s)
- H Stegmann
- II. Physiologisches Institut, Universität Heidelberg, Germany
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22
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Ramachandran S, Thomas DD. Rotational dynamics of the regulatory light chain in scallop muscle detected by time-resolved phosphorescence anisotropy. Biochemistry 1999; 38:9097-104. [PMID: 10413484 DOI: 10.1021/bi9902945] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We have used time-resolved phosphorescence anisotropy (TPA) to study the rotational dynamics of chicken gizzard regulatory light chain (RLC) bound to scallop adductor muscle myofibrils in key physiological states. Native RLC from scallop myofibrils was extracted and replaced completely with gizzard RLC labeled specifically at Cys 108 with erythrosin iodoacetamide (ErIA). The calcium sensitivity of the ATPase activity of the labeled myofibril preparation was quite similar to that of the native sample, indicating that the ErIA-labeled RLC is functionally bound to the myosin head. In rigor (in the absence of ATP, when all the myosin heads are rigidly bound to the thin filament), a slight decay was observed in the first few microseconds, followed by no change in the anisotropy. This indicates small-amplitude restricted motions of the RLC or the entire LC domain of myosin. Addition of calcium to rigor restricts these motions further. Relaxation with ATP (no Ca) causes a large decay in the anisotropy, indicating large-amplitude rotational motion with correlation times of 5-50 micros. Further addition of calcium, to induce contraction, resulted in a decrease in the rate and amplitude of anisotropy decay. In particular, there is clear evidence for a slow rotational motion with a correlation time of approximately 300 micros, which is not present either in rigor or relaxation. This indicates rotational motion that specifically correlates with force generation. The changes in the rotational dynamics of the light-chain domain in rigor, relaxation, and contraction support earlier work based on probes of the catalytic domain that muscle contraction is accompanied by a disorder-to-order transition of the myosin head. However, the motions of the LC domain are different from those of the catalytic domain, which indicates rotation of the two domains relative to each other.
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Affiliation(s)
- S Ramachandran
- Department of Biochemistry, University of Minnesota Medical School, Minneapolis 55455, USA
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23
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Tsaturyan AK, Bershitsky SY, Burns R, Ferenczi MA. Structural changes in the actin-myosin cross-bridges associated with force generation induced by temperature jump in permeabilized frog muscle fibers. Biophys J 1999; 77:354-72. [PMID: 10388763 PMCID: PMC1300335 DOI: 10.1016/s0006-3495(99)76895-5] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
Structural changes induced by Joule temperature jumps (T-jumps) in frog muscle fibers were monitored using time-resolved x-ray diffraction. Experiments made use of single, permeabilized fibers that were fully activated after slight cross-linking with 1-ethyl-3-[3-dimethylamino)propyl]carbodiimide to preserve their structural order. After T-jumps from 5-6 to approximately 17 degrees C and then on to approximately 30 degrees C, tension increased by a factor of 1.51 and 1.84, respectively, whereas fiber stiffness did not change with temperature. The tension rise was accompanied by a decrease in the intensity of the (1, 0) equatorial x-ray reflection by 15 and 26% (at approximately 17 and approximately 30 degrees C) and by an increase in the intensity of the M3 myosin reflection by 20% and 41%, respectively. The intensity of the (1,1) equatorial reflection increased slightly. The peak of the intensity on the 6th actin layer line shifted toward the meridian with temperature. The intensity of the 1st actin layer line increased from 12% (of its rigor value) at 5-6 degrees C to 36% at approximately 30 degrees C, so that the fraction of the cross-bridges labeling the actin helix estimated from this intensity increased proportionally to tension from approximately 35% at 5-6 degrees C to approximately 60% at approximately 30 degrees C. This suggests that force is generated during a transition of nonstereo-specifically attached myosin cross-bridges to a stereo-specific binding state.
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Affiliation(s)
- A K Tsaturyan
- Institute of Mechanics, Moscow University, Mitchurinsky prosp. 1, Moscow 119899, Russia
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24
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Aydos RD, Silva IS, Goldenberg S, Goldenberg A, Simões MDJ, Takita LC, Nigro AJT. ESTUDO COMPARATIVO DO EFEITO DAS TELAS DE POLITETRAFLUOROETILENO EXPANDIDO E DE POLIPROPILENO, COLOCADAS POR LAPAROSCOPIA, EM HÉRNIAS VENTRAIS PRODUZIDAS EM COELHOS. Acta Cir Bras 1999. [DOI: 10.1590/s0102-86501999000200002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Estudou-se o efeito das telas de politetrafluoroetileno expandido (PTFE) e polipropileno (PP), colocadas por laparoscopia, em hérnias incisionais produzidas experimentalmente. Utilizou-se 45 coelhos, distribuídos em três grupos: PP (tela de PP), PTFE (tela de PTFE) e C (grupo controle, sem tela). Em todos os animais foi inicialmente produzida uma hérnia incisional. Trinta dias após, foram submetidos a laparoscopia e as hérnias foram tratadas com telas de PP ou de PTFE, colocadas de forma intraperitoneal. Nos animais controle foi somente realizada, quando presentes, a lise de aderências,. Trinta e cinco dias após este procedimento foi realizada laparoscopia para a observação de aderências à região da tela (grupo PTFE e PP) ou da hérnia (grupo C), de aderências intestinais, nestas regiões e ainda para observar recidivas e o aspecto da tela (esticado ou enrugado) . Aos 70 dias da colocação das telas, os animais foram submetidos a eutanásia e novamente estudados quanto à presença de aderências, quanto à recidiva e ao aspecto da tela. A parede abdominal, foi ainda submetida a exame histológico, com contagem das fibras colágenas e a estudo da força de ruptura. Não ocorreram recidivas das hérnias nos grupos tratados. O grupo PP apresentou, aos 35 e 70 dias, incidência significativamente maior de aderências e do número de fibras colágenas em relação ao grupo PTFE e ao grupo C. A força de ruptura foi estatisticamente semelhante nos 3 grupos.
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25
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Katayama E, Ohmori G, Baba N. Three-dimensional image analysis of myosin head in function as captured by quick-freeze deep-etch replica electron microscopy. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1999; 453:37-45. [PMID: 9889812 DOI: 10.1007/978-1-4684-6039-1_5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Quick-freeze deep-etch replica electron microscopy combined with mica-flake technique provides high contrast, high time- and spatial-resolution images of protein molecules in solution, whose three-dimensional structure is well preserved. Thus, it might be quite useful to obtain structural information of individual functioning molecules, such as myosin crossbridges under in vitro motility assay conditions. With that method, we could actually show that both heads of heavy meromyosin (HMM) crossbridges are mostly straight and bound to actin filaments with about 45 degree tilt-angle under rigor conditions, whereas they attached to actin through only one head with a wide variety of angles under in vitro sliding conditions. We also demonstrated that free HMM heads are strongly kinked in the presence of ATP or ADP/inorganic vanadate (Vi) in contrast to almost straight configuration in the absence of nucleotide. To examine more detailed structure of individual crossbridges, we tried to reconstruct the three-dimensional architecture of intramolecular subdomains of single HMM molecule. We took a series of tilted images of single HMM-ADP/Vi particle and successfully obtained its 3-D image by filtered back-projection, even with restricted range of tilt-angles. By comparison of the reconstruction with the atomic model of subfragment-1 (S1) without nucleotide, we found some great structural difference, which partly might be attributable to the conformational change by nucleotide binding.
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Affiliation(s)
- E Katayama
- Department of Fine Morphology, University of Tokyo, Japan
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26
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TOGNINI JOÃORICARDOF, DANIELA NEVES, SOUZA ALEXSANDRODE, AYDOS RICARDODUTRA. EFEITO DA CONSERVAÇÃO POR FORMAS DE CONGELAMENTO NA AVALIAÇÃO DA FORÇA DE ROTURA DE CICATRIZES DA PAREDE ABDOMINAL DE RATOS. Acta Cir Bras 1998. [DOI: 10.1590/s0102-86501998000400010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
O objetivo deste trabalho foi o de estudar o efeito de duas formas de congelamento na avaliação da força de rotura de cicatrizes da parede abdominal de ratos. Foram utilizados 30 ratos machos Wistar, submetidos a laparotomia com técnica de diérese padronizada, distribuidos em 3 grupos com 10 ratos cada. No 14<FONT FACE="Symbol">°</FONT> dia de pós-operatório foram submetidos a eutanásia os ratos de dois grupos que tiveram segmentos músculo-fasciais da parede abdominal envolvendo a cicatriz cirúrgica, conservados em congelador a dezessete graus Célsius negativos (-17<FONT FACE="Symbol">°</FONT> C) ou em anidrido carbônico a oitenta graus célsius negativos (-80<FONT FACE="Symbol">°</FONT> C) por 20 dias antes de terem sidos submetidos a análise da força de rotura da cicatriz em um tensiômetro. O terceiro grupo (controle) foi submetido a eutanásia e imediatamente avaliado quanto a força de rotura. Os resultados encontrados foram analisados estatísticamente. Concluiu-se que as duas formas de congelamento não interferem na avaliação da força de rotura de cicatrizes da parede abdominal de ratos.
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27
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White HD, Walker ML, Trinick J. A computer-controlled spraying-freezing apparatus for millisecond time-resolution electron cryomicroscopy. J Struct Biol 1998; 121:306-13. [PMID: 9704502 DOI: 10.1006/jsbi.1998.3968] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Apparatus is described for the kinetic investigation of biological reactions by electron cryomicroscopy with time resolution on the order of milliseconds. This involves layering a grid with one reactant and then spraying on a second reactant immediately before freezing. Two-stage mixing can be achieved by mixing two solutions, holding them in a delay line for a preset interval, and then spraying the aged solution onto a grid carrying a third reactant. The individual steps of these procedures are under software control and can be adjusted independently. Spray-freezing is widely applicable since solutions of small molecules, proteins, and protein assemblies can be delivered as aerosols. Thus the method can be used to study both the effects of small molecules on macromolecules and for monitoring protein-protein interactions. It may also be useful in other situations, for instance in light microscopy.
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Affiliation(s)
- H D White
- Department of Biochemistry, Eastern Virginia Medical School, Norfolk 23507, USA
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28
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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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29
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Baker JE, Brust-Mascher I, Ramachandran S, LaConte LE, Thomas DD. A large and distinct rotation of the myosin light chain domain occurs upon muscle contraction. Proc Natl Acad Sci U S A 1998; 95:2944-9. [PMID: 9501195 PMCID: PMC19674 DOI: 10.1073/pnas.95.6.2944] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/1997] [Indexed: 02/06/2023] Open
Abstract
For more than 30 years, the fundamental goal in molecular motility has been to resolve force-generating motor protein structural changes. Although low-resolution structural studies have provided evidence for force-generating myosin rotations upon muscle activation, these studies did not resolve structural states of myosin in contracting muscle. Using electron paramagnetic resonance, we observed two distinct orientations of a spin label attached specifically to a single site on the light chain domain of myosin in relaxed scallop muscle fibers. The two probe orientations, separated by a 36 degrees +/- 5 degrees axial rotation, did not change upon muscle activation, but the distribution between them changed substantially, indicating that a fraction (17% +/- 2%) of myosin heads undergoes a large (at least 30 degrees) axial rotation of the myosin light chain domain upon force generation and muscle contraction. The resulting model helps explain why this observation has remained so elusive and provides insight into the mechanisms by which motor protein structural transitions drive molecular motility.
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Affiliation(s)
- J E Baker
- Department of Biochemistry, University of Minnesota Medical School, Minneapolis, MN 55455, USA
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30
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Tregear RT, Edwards RJ, Irving TC, Poole KJ, Reedy MC, Schmitz H, Towns-Andrews E, Reedy MK. X-ray diffraction indicates that active cross-bridges bind to actin target zones in insect flight muscle. Biophys J 1998; 74:1439-51. [PMID: 9512040 PMCID: PMC1299490 DOI: 10.1016/s0006-3495(98)77856-7] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
We report the first time-resolved study of the two-dimensional x-ray diffraction pattern during active contraction in insect flight muscle (IFM). Activation of demembranated Lethocerus IFM was triggered by 1.5-2.5% step stretches (risetime 10 ms; held for 1.5 s) giving delayed active tension that peaked at 100-200 ms. Bundles of 8-12 fibers were stretch-activated on SRS synchrotron x-ray beamline 16.1, and time-resolved changes in diffraction were monitored with a SRS 2-D multiwire detector. As active tension rose, the 14.5- and 7.2-nm meridionals fell, the first row line dropped at the 38.7 nm layer line while gaining a new peak at 19.3 nm, and three outer peaks on the 38.7-nm layer line rose. The first row line changes suggest restricted binding of active myosin heads to the helically preferred region in each actin target zone, where, in rigor, two-headed lead bridges bind, midway between troponin bulges that repeat every 38.7 nm. Halving this troponin repeat by binding of single active heads explains the intensity rise at 19.3 nm being coupled to a loss at 38.7 nm. The meridional changes signal movement of at least 30% of all myosin heads away from their axially ordered positions on the myosin helix. The 38.7- and 19.3-nm layer line changes signal stereoselective attachment of 7-23% of the myosin heads to the actin helix, although with too little ordering at 6-nm resolution to affect the 5.9-nm actin layer line. We conclude that stretch-activated tension of IFM is produced by cross-bridges that bind to rigor's lead-bridge target zones, comprising < or = 1/3 of the 75-80% that attach in rigor.
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Affiliation(s)
- R T Tregear
- MRC Laboratory of Molecular Biology, Cambridge, England.
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31
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Bershitsky SY, Tsaturyan AK, Bershitskaya ON, Mashanov GI, Brown P, Burns R, Ferenczi MA. Muscle force is generated by myosin heads stereospecifically attached to actin. Nature 1997; 388:186-90. [PMID: 9217160 DOI: 10.1038/40651] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Muscle force is generated by myosin crossbridges interacting with actin. As estimated from stiffness and equatorial X-ray diffraction of muscle and muscle fibres, most myosin crossbridges are attached to actin during isometric contraction, but a much smaller fraction is bound stereospecifically. To determine the fraction of crossbridges contributing to tension and the structural changes that attached crossbridges undergo when generating force, we monitored the X-ray diffraction pattern during temperature-induced tension rise in fully activated permeabilized frog muscle fibres. Temperature jumps from 5-6 degrees C to 16-19 degrees C initiated a 1.7-fold increase in tension without significantly changing fibre stiffness or the intensities of the (1,1) equatorial and (14.5 nm)(-1) meridional X-ray reflections. However, tension rise was accompanied by a 20% decrease in the intensity of the (1,0) equatorial reflection and an increase in the intensity of the first actin layer line by approximately 13% of that in rigor. Our results show that muscle force is associated with a transition of the crossbridges from a state in which they are nonspecifically attached to actin to one in which stereospecifically bound myosin crossbridges label the actin helix.
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Affiliation(s)
- S Y Bershitsky
- National Institute for Medical Research, Mill Hill, London, UK
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32
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Park S, Ajtai K, Burghardt TP. Optical activity of a nucleotide-sensitive tryptophan in myosin subfragment 1 during ATP hydrolysis. Biophys Chem 1996; 63:67-80. [PMID: 8981751 DOI: 10.1016/s0301-4622(96)02203-x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The xanthene probes 5'-iodoacetamido-fluorescein and -tetramethylrhodamine specifically modify skeletal muscle myosin subfragment 1 (S1) at the reactive thiol residue (SH1) and fully quench the fluorescence emission from tryptophan residue 510 (Trp510) in S1 (T.P. Burghardt and K. Ajtai, Biophys. Chem., 60 (1996) 119; K. Ajtai and T.P. Burghardt, Biochemistry, 34 (1995) 15943). The difference between the fluorescence intensity obtained from S1 and probe-modified S1 comes solely from Trp510 in chymotryptic S1, a protein fragment that contains five tryptophan residues. The rotary strength and quantum efficiency of Trp510 were measured using difference signals from fluorescence detected circular dichroism (FDCD) and fluorescence emission spectroscopy. These structure-sensitive signals indicate that the binding of nucleotide or nucleotide analogs to the active site of S1 causes structural changes in S1 at Trp510 and that a one-to-one correspondence exists between Trp510 conformation and transient states of myosin during contraction. The Trp510 rotary strength and quantum efficiency were interpreted structurally in terms of the indole side-chain conformation using model structures and established computational methods.
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Affiliation(s)
- S Park
- Department of Biochemistry and Molecular Biology, Mayo Foundation, Rochester, MN 55905, USA
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33
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Lenart TD, Murray JM, Franzini-Armstrong C, Goldman YE. Structure and periodicities of cross-bridges in relaxation, in rigor, and during contractions initiated by photolysis of caged Ca2+. Biophys J 1996; 71:2289-306. [PMID: 8913571 PMCID: PMC1233720 DOI: 10.1016/s0006-3495(96)79464-x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Ultra-rapid freezing and electron microscopy were used to directly observe structural details of frog muscle fibers in rigor, in relaxation, and during force development initiated by laser photolysis of DM-nitrophen (a caged Ca2+). Longitudinal sections from relaxed fibers show helical tracks of the myosin heads on the surface of the thick filaments. Fibers frozen at approximately 13, approximately 34, and approximately 220 ms after activation from the relaxed state by photorelease of Ca2+ all show surprisingly similar cross-bridge dispositions. In sections along the 1,1 lattice plane of activated fibers, individual cross-bridge densities have a wide range of shapes and angles, perpendicular to the fiber axis or pointing toward or away from the Z line. This highly variable distribution is established very early during development of contraction. Cross-bridge density across the interfilament space is more uniform than in rigor, wherein the cross-bridges are more dense near the thin filaments. Optical diffraction (OD) patterns and computed power density spectra of the electron micrographs were used to analyze periodicities of structures within the overlap regions of the sarcomeres. Most aspects of these patterns are consistent with time resolved x-ray diffraction data from the corresponding states of intact muscle, but some features are different, presumably reflecting different origins of contrast between the two methods and possible alterations in the structure of the electron microscopy samples during processing. In relaxed fibers, OD patterns show strong meridional spots and layer lines up to the sixth order of the 43-nm myosin repeat, indicating preservation and resolution of periodic structures smaller than 10 nm. In rigor, layer lines at 18, 24, and 36 nm indicate cross-bridge attachment along the thin filament helix. After activation by photorelease of Ca2+, the 14.3-nm meridional spot is present, but the second-order meridional spot (22 nm) disappears. The myosin 43-nm layer line becomes less intense, and higher orders of 43-nm layer lines disappear. A 36-nm layer line is apparent by 13 ms and becomes progressively stronger while moving laterally away from the meridian of the pattern at later times, indicating cross-bridges labeling the actin helix at decreasing radius.
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Affiliation(s)
- T D Lenart
- Pennsylvania Muscle Institute, Department of Physiology, University of Pennsylvania, Philadelphia 19104, USA
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34
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Díaz Baños FG, Bordas J, Lowy J, Svensson A. Small segmental rearrangements in the myosin head can explain force generation in muscle. Biophys J 1996; 71:576-89. [PMID: 8842197 PMCID: PMC1233515 DOI: 10.1016/s0006-3495(96)79292-5] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Poisson-Boltzmann calculations of the distribution of electrostatic potentials around an actin filament in physiological-strength solutions show that negative isopotential surfaces protrude into the solvent. Each protrusion follows the actin two-start helix and is located on the sites implicated in the formation of the actomyosin complex. Molecular dynamic calculations on the S1 portion of the myosin molecule indicate that in the presence of ATP the crystallographically invisible loops (comprising residues 624-649 and 564-579) remain on the surface, whereas in the absence of ATP they can move toward the actin-binding sites and experience electrostatic forces that range from 1 to 10 pN. The molecular dynamics calculations also suggest that during the ATP cycle there exist at least three states of electrostatic interactions between the loops and actin. Every time a new interaction is formed, the strain in the myosin head increases and the energy of the complex decreases by 2kT to 5kT. This can explain muscular contraction in terms of a Huxley-Simmons-type mechanism, while requiring only rearrangements of small mobile S1 segments rather than the large shape changes in the myosin molecule postulated by the conventional tilting head model.
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Affiliation(s)
- F G Díaz Baños
- Departamento de Química Física, Universidad de Murcia, Spain
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35
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Abstract
In this paper, the rotating cross-bridge mechanism for muscle contraction is discussed and much contradictory evidence is put forward. As an alternative, a model is given in which the motor of muscle contraction is placed in the myosin-rod hinge and/or in the actin filament. No definite choice for one of the proposed models can be made yet, although it is clear that some kind of phase transition plays an important role in the mechanism.
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Affiliation(s)
- G H Pollack
- University of Washington, Seattle 98195, USA.
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36
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Adhikari BB, Fajer PG. Myosin head orientation and mobility during isometric contraction: effects of osmotic compression. Biophys J 1996; 70:1872-80. [PMID: 8785347 PMCID: PMC1225157 DOI: 10.1016/s0006-3495(96)79752-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
We have correlated the mobility and the generation of force of myosin heads by applying radial compression to isometrically contracting muscle fibers. Osmotic pressure was produced by dextran T-500, and its effect on the orientation and mobility of myosin heads labeled with N-(1-oxy-2,2,5,5-tetramethyl-4-pyperidinyl)maleimide was observed by conventional and saturation-transfer electron paramagnetic resonance methods. A biphasic behavior is spectral changes coinciding with the tension dependence was observed as the fibers were compressed. At diameters above the equilibrium spacing, the large myosin head disorder characteristic during contraction in the absence of compression was largely maintained, whereas the mobility decreased threefold, from tauR approximately 25 microseconds to approximately 80-90 microseconds. The inhibition of fast microsecond motions was not accompanied by tension loss, implying that these motions are not necessary for force generation. At diameters below the equilibrium spacing, both the disorder and the mobility decreased dramatically in parallel with the tension inhibition, suggesting that slower microsecond motions and the disorder of the myosin head are necessary for muscle function.
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Affiliation(s)
- B B Adhikari
- Institute of Molecular Biophysics, Florida State University, Tallahassee 32306, USA
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37
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Abstract
A mechanism is proposed for molecular motors in which force is generated by a protein conformational change driven by binding energy (in muscle, that of myosin with actin as well as with ATP, ADP, or Pi). Work, the product of the force generated by one myosin or kinesin molecule (F) and the distance over which it acts (d), is a function of a ratio of dissociation constants before and after the contractile step: F.d < RT ln(KAe/KAc). From published data the ratio is > 2 x 10(4), which can be explained by conversion of a surface complex to an enclosed, or partly enclosed, complex. Although the complex performing the work stroke is in unstrained conformation, the complex after the work stroke is much more stable, owing to binding forces; the latter, however, is destabilized by the load, which thereby opposes the contractile conformational change, countering the force-generating reaction. The connection between the free energy release and work is implicit in the mechanism, inasmuch as coupling, like force generation, depends on conformational changes driven by binding energy (internal rather than external work being involved in coupling). The principles apply whether ATP or an ion gradient drives the system. At high load, in muscle, the mechanism allows for a summation of the forces generated by several myosin molecules.
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Affiliation(s)
- R M Krupka
- Pest Management Research Centre, London, Ontario, Canada
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38
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Allen TS, Ling N, Irving M, Goldman YE. Orientation changes in myosin regulatory light chains following photorelease of ATP in skinned muscle fibers. Biophys J 1996; 70:1847-62. [PMID: 8785345 PMCID: PMC1225155 DOI: 10.1016/s0006-3495(96)79750-3] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The orientation of the light-chain region of myosin heads in muscle fibers was followed by polarized fluorescence from an extrinsic probe during tension transients elicited by photolysis of caged ATP. Regulatory light chain from chicken gizzard myosin was covalently modified with iodoacetamidotetramethylrhodamine and exchanged into skinned fibers from rabbit psoas muscle without significant effect of the tension transients. Fluorescence polarization ratios Q parallel = (parallel I parallel-perpendicular I parallel)/ (parallel I parallel+perpendicular I parallel) and Q perpendicular = perpendicular I perpendicular - parallel I perpendicular)/ (perpendicular I perpendicular + parallel I perpendicular), where mIn denote fluorescence intensities for excitation (pre-subscript) and emission (post-subscript) parallel or perpendicular to the fiber axis, were simultaneously measured at 0.5 ms time resolution. Q perpendicular decreased and Q parallel increased promptly after ATP release in the presence or absence of CA2+, indicating changes in orientation of the light-chain region associated with ATP binding or cross-bridge detachment. Little further change in the Q signals accompanied either active tension development (+Ca2+) or the final relaxation (-Ca2+). The Q and tension transients slowed when liberated ATP concentration was reduced. Assuming that ATP is released at 118 s-1 (20 degrees C), the apparent second-order rate constants were 3-10 x 10(5) M-1 s-1 for Q parallel, 1-5 x 10(5) M-1 s-1 for Q perpendicular, and 0.5-2 x 10(5) M-1 s-1 for the convergence of tension traces starting from different rigor values. Fitting of model orientation distributions to the Q signals indicated that the angular disorder increases after ATP binding. This orientation change is specific to ATP because photo release of ADP caused much smaller changes in the Q signals.
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Affiliation(s)
- T S Allen
- Pennsylvania Muscle Institute, University of Pennsylvania, Philadelphia 19104-6083, USA
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39
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Higuchi H, Goldman YE. Sliding distance per ATP molecule hydrolyzed by myosin heads during isotonic shortening of skinned muscle fibers. Biophys J 1995; 69:1491-507. [PMID: 8534820 PMCID: PMC1236380 DOI: 10.1016/s0006-3495(95)80020-2] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
We measured isotonic sliding distance of single skinned fibers from rabbit psoas muscle when known and limited amounts of ATP were made available to the contractile apparatus. The fibers were immersed in paraffin oil at 20 degrees C, and laser pulse photolysis of caged ATP within the fiber initiated the contraction. The amount of ATP released was measured by photolyzing 3H-ATP within fibers, separating the reaction products by high-pressure liquid chromatography, and then counting the effluent peaks by liquid scintillation. The fiber stiffness was monitored to estimate the proportion of thick and thin filament sites interacting during filament sliding. The interaction distance, Di, defined as the sliding distance while a myosin head interacts with actin in the thin filament per ATP molecule hydrolyzed, was estimated from the shortening distance, the number of ATP molecules hydrolyzed by the myosin heads, and the stiffness. Di increased from 11 to 60 nm as the isotonic tension was reduced from 80% to 6% of the isometric tension. Velocity and Di increased with the concentration of ATP available. As isotonic load was increased, the interaction distance decreased linearly with decrease of the shortening velocity and extrapolated to 8 nm at zero velocity. Extrapolation of the relationship between Di and velocity to saturating ATP concentration suggests that Di reaches 100-190 nm at high shortening velocity. The interaction distance corresponds to the sliding distance while cross-bridges are producing positive (working) force plus the distance while they are dragging (producing negative forces). The results indicate that the working and drag distances increase as the velocity increases. Because Di is larger than the size of either the myosin head or the actin monomer, the results suggest that for each ATPase cycle, a myosin head interacts mechanically with several actin monomers either while working or while producing drag.
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Affiliation(s)
- H Higuchi
- Department of Physiology, University of Pennsylvania, Philadelphia 19104-6083, USA
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40
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Veigel C, v Maydell RD, Wiegand-Steubing R, Goody R, Fink HA. The influence of ionic strength upon relaxation from rigor induced by flash photolysis of caged-ATP in skinned murine skeletal muscle fibres. Pflugers Arch 1995; 430:994-1003. [PMID: 8594553 DOI: 10.1007/bf01837414] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The influence of ionic strength upon relaxation kinetics from rigor in skinned murine extensor digitorum longus (EDL) skeletal muscle fibres was examined using photolysis of caged-ATP at low Ca2+. The ionic strength was adjusted with either KMeSO3 or ethylene glycolbis-(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid, dipotassium salt (K2EGTA) in the range of tau /2 = 65-215mM, or I.E. 49-194mM, where I.E. denotes ionic equivalent. Following rigor development at a tau /2 of 165-215mM (I.E. 144-194mM), the liberation of approximately 0.5mM ATP resulted in an initial 6-to 10-ms detachment phase with a decline in force of approximately 10-20% followed by a 10-to 30-ms reattachment with up to a 60% increase compared to the corresponding rigor level and a final detachment leading to complete relaxation. Interestingly, when similar ATP concentrations were liberated at lower ionic strengths between a tau /2 of 65mM and 110mM (I.E. 60-100mM), the initial detachment phase was shortened and force decreased by only approximately 5-10%, while the following reattachment phase was lengthened and led to an increased steady-state force of approximately 20-80% without final relaxation. ATP-induced detachment and subsequent reattachment were mainly determined by the currently present ionic strength and were relatively independent of the preceding rigor state which had been developed at higher or lower ionic strengths. The effects of phosphate and apyrase on the force transient suggest that reattachment of ADP- binding crossbridges may contribute to the increase in tension at high and even more at low ionic strengths. The study shows that the kinetics of initial fast relaxation and subsequent redevelopment of force following flash photolysis of similar ATP concentrations are markedly modified by the ionic strength in the narrow range of between 65mM and 215mM.
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Affiliation(s)
- C Veigel
- II. Institute of Physiology, University of Heidelberg, Im Neuenheimer Feld 326, D-69120 Heidelberg, Germany
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41
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Zhao L, Pate E, Baker AJ, Cooke R. The myosin catalytic domain does not rotate during the working power stroke. Biophys J 1995; 69:994-9. [PMID: 8519999 PMCID: PMC1236328 DOI: 10.1016/s0006-3495(95)79974-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Electron paramagnetic resonance spectroscopy of a spin probe attached to cys-707 on myosin cross-bridges was used to monitor the orientation of the myosin catalytic domain at the beginning and end of the working power stroke in active muscle. Elevated concentrations of orthophosphate and decreased pH were used to shift the population of cross-bridges from force-producing states into low force, pre-power-stroke states. The spectrum of probes in active fibers was not changed by conditions that reduced tension by 70%, indicating that the orientation of the catalytic domain was the same at the beginning and end of the power stroke. Thus the data show that the catalytic domain remains rigidly oriented on the actin filament during the power stroke.
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Affiliation(s)
- L Zhao
- Department of Biochemistry and Biophysics, University of California, San Francisco 94143, USA
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42
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Sekimoto K, Tawada K. Extended time correlation of in vitro motility by motor protein. PHYSICAL REVIEW LETTERS 1995; 75:180-183. [PMID: 10059145 DOI: 10.1103/physrevlett.75.180] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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43
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Ostap EM, Barnett VA, Thomas DD. Resolution of three structural states of spin-labeled myosin in contracting muscle. Biophys J 1995; 69:177-88. [PMID: 7669895 PMCID: PMC1236236 DOI: 10.1016/s0006-3495(95)79888-5] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
We have used electron paramagnetic resonance (EPR) spectroscopy to detect ATP- and calcium-induced changes in the structure of spin-labeled myosin heads in glycerinated rabbit psoas muscle fibers in key physiological states. The probe was a nitroxide iodoacetamide derivative attached selectively to myosin SH1 (Cys 707), the conventional EPR spectra of which have been shown to resolve several conformational states of the myosin ATPase cycle, on the basis of nanosecond rotational motion within the protein. Spectra were acquired in rigor and during the steady-state phases of relaxation and isometric contraction. Spectral components corresponding to specific conformational states and biochemical intermediates were detected and assigned by reference to EPR spectra of trapped kinetic intermediates. In the absence of ATP, all of the myosin heads were rigidly attached to the thin filament, and only a single conformation was detected, in which there was no sub-microsecond probe motion. In relaxation, the EPR spectrum resolved two conformations of the myosin head that are distinct from rigor. These structural states were virtually identical to those observed previously for isolated myosin and were assigned to the populations of the M*.ATP and M**.ADP.Pi states. During isometric contraction, the EPR spectrum resolves the same two conformations observed in relaxation, plus a small fraction (20-30%) of heads in the oriented actin-bound conformation that is observed in rigor. This rigor-like component is a calcium-dependent, actin-bound state that may represent force-generating cross-bridges. As the spin label is located near the nucleotide-binding pocket in a region proposed to be pivotal for large-scale force-generating structural changes in myosin, we propose that the observed spectroscopic changes indicate directly the key steps in energy transduction in the molecular motor of contracting muscle.
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Affiliation(s)
- E M Ostap
- Department of Biochemistry, University of Minnesota Medical School, Minneapolis 55455, USA
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44
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Hawkins CJ, Bennett PM. Evaluation of freeze substitution in rabbit skeletal muscle. Comparison of electron microscopy to X-ray diffraction. J Muscle Res Cell Motil 1995; 16:303-18. [PMID: 7560003 DOI: 10.1007/bf00121139] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Rabbit psoas muscle fibres, relaxed and in rigor, have been freeze substituted for electron microscopy. Fourier transforms and average density maps of micrographs of transverse sections have been obtained and compared to X-ray diffraction data. The Fourier amplitudes from rigor and relaxed muscle are comparable to equatorial data from X-ray diffraction of muscle if there is more disorder in the electron micrographs which can be described by a 'temperature' factor. The phases of reflections out to the 3,2 have been determined; those reflections at the same radius and therefore not separable in the X-ray patterns, such as the 2,1 and the 1,2, are separated in the transforms of sections through the A band. In transforms from both rigor and relaxed muscle they have the same phase. In rigor muscle they have different amplitudes. All the phases are positive or negative showing that the lattice is centrosymmetric at the resolution obtained. The phases obtained generally support those suggested by model building studies using X-ray diffraction data. In rigor muscle, areas where the cross-bridges are regularly attached are clearly seen in thin transverse sections. A handedness to this structure is indicated by a lack of mirror symmetry, in both the Fourier transform of thick sections, and in the averaged density map. This correlates well with the arrangement where the myosin head is bound as in the acto-S1 structure but only to actin monomers within a limited azimuthal range.
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Affiliation(s)
- C J Hawkins
- MRC Muscle and Cell Motility Unit, Randall Institute, King's College London, UK
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45
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Raucher D, Fajer EA, Sár C, Hideg K, Zhao Y, Kawai M, Fajer PG. A novel electron paramagnetic resonance spin label and its application to study the cross-bridge cycle. Biophys J 1995; 68:128S-133S; discussion 134S. [PMID: 7787055 PMCID: PMC1281893] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
We have used a novel alpha-iodoketone spin-label (IKSL) to study myosin head orientation and cross-bridge dynamics in the putative pre-powerstroke state. Possible perturbation of the cross-bridge cycle by the label was assayed by the sinusoidal analysis method (Kawai and Brandt, 1980; Kawai and Zhao, 1993), which determines the rate constants of the elementary steps in the cycle. A comparison of the rates obtained from unlabeled and IKSL fibers revealed small (10-20%) changes in the ATP hydrolysis rate and in the rate constants of the elementary steps. The labeling induced small changes (< 13%) in the distribution of the cross-bridges among the various intermediate states. Pre-powerstroke cross-bridges were induced by aluminum fluoride in the presence of Ca2+ and ATP. In this state, force development is inhibited, but a large proportion (40%) of the cross-bridges are still attached to the thin filament. We have used conventional electron paramagnetic resonance to measure orientation, and have found that the pre-powerstroke heads are as disordered as in relaxation. Their mobility, as determined by saturation transfer electron paramagnetic resonance, was significantly restricted. Assuming that stiffness is proportional to the fraction of strongly attached heads, the rotational correlation time of the bound heads is estimated to be tau r = approximately 150-400 microseconds.
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Affiliation(s)
- D Raucher
- Institute of Molecular Biophysics, Florida State University, Tallahassee 32306, USA
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46
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Allen TS, Sabido-David C, Ling N, Irving M, Goldman YE. Transients of fluorescence polarization in skeletal muscle fibers labeled with rhodamine on the regulatory light chain. Biophys J 1995; 68:81S-84S; discussion 85S-86S. [PMID: 7787113 PMCID: PMC1281879] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Structural changes of the myosin heads were correlated with mechanical events in the cross-bridge cycle by measuring fluorescence polarization signals at high time resolution from rhodamine probes bound to myosin regulatory light chains in skeletal muscle fibers. Motions of the cross-bridges were partially synchronized either by applying quick length changes to the fibers during active contractions or by activating the fibers from rigor by photolysis of caged ATP in the presence of Ca2+. With fibers in rigor, the fluorescence polarization values indicate that the probe dipoles are quite well ordered and are directed away from the muscle fiber axis. After photorelease of ATP from caged ATP, changes in polarization signals are consistent with broadening of the distribution of probe orientations. The signal deflections occur when ATP binds to actomyosin or when the cross-bridges detach, but the orientational distribution changes surprisingly little during active force development. In contrast, when staircases of quick releases are applied to labeled fibers during active contractions, the fluorescence polarization signals suggest a concerted rotation of the probes. The results indicate that the light chain region of myosin tilts during the quick release and/or during the tension recovery phase within the next few ms.
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Affiliation(s)
- T S Allen
- Pennsylvania Muscle Institute, University of Pennsylvania, Philadelphia 19104, USA
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47
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Roopnarine O, Thomas DD. Orientational dynamics of indane dione spin-labeled myosin heads in relaxed and contracting skeletal muscle fibers. Biophys J 1995; 68:1461-71. [PMID: 7787032 PMCID: PMC1282041 DOI: 10.1016/s0006-3495(95)80319-x] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
We have used electron paramagnetic resonance (EPR) spectroscopy to study the orientation and rotational motions of spin-labeled myosin heads during steady-state relaxation and contraction of skinned rabbit psoas muscle fibers. Using an indane-dione spin label, we obtained EPR spectra corresponding specifically to probes attached to Cys 707 (SH1) on the catalytic domain of myosin heads. The probe is rigidly immobilized, so that it reports the global rotation of the myosin head, and the probe's principal axis is aligned almost parallel with the fiber axis in rigor, making it directly sensitive to axial rotation of the head. Numerical simulations of EPR spectra showed that the labeled heads are highly oriented in rigor, but in relaxation they have at least 90 degrees (Gaussian full width) of axial disorder, centered at an angle approximately equal to that in rigor. Spectra obtained in isometric contraction are fit quite well by assuming that 79 +/- 2% of the myosin heads are disordered as in relaxation, whereas the remaining 21 +/- 2% have the same orientation as in rigor. Computer-simulated spectra confirm that there is no significant population (> 5%) of heads having a distinct orientation substantially different (> 10 degrees) from that in rigor, and even the large disordered population of heads has a mean orientation that is similar to that in rigor. Because this spin label reports axial head rotations directly, these results suggest strongly that the catalytic domain of myosin does not undergo a transition between two distinct axial orientations during force generation. Saturation transfer EPR shows that the rotational disorder is dynamic on the microsecond time scale in both relaxation and contraction. These results are consistent with models of contraction involving 1) a transition from a dynamically disordered preforce state to an ordered (rigorlike) force-generating state and/or 2) domain movements within the myosin head that do not change the axial orientation of the SH1-containing catalytic domain relative to actin.
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Affiliation(s)
- O Roopnarine
- Department of Biochemistry, University of Minnesota Medical School, Minneapolis 55455, USA
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48
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Mao M, Andreev O, Borejdo J. Rigor cross-bridges bind to two actin monomers inthin filaments of rabbit psoas muscle. J Mol Biol 1995. [DOI: 10.1016/s0022-2836(95)80051-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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49
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Three recent breakthroughs in molecular motor research: recombinant myosin, monomolecular in vitro motility assay and atomic structure of S1. MATERIALS SCIENCE & ENGINEERING. C, MATERIALS FOR BIOLOGICAL APPLICATIONS 1994. [DOI: 10.1016/0928-4931(94)90022-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Hirose K, Franzini-Armstrong C, Goldman YE, Murray JM. Structural changes in muscle crossbridges accompanying force generation. J Biophys Biochem Cytol 1994; 127:763-78. [PMID: 7962058 PMCID: PMC2120236 DOI: 10.1083/jcb.127.3.763] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
We have investigated the structure of the crossbridges in muscles rapidly frozen while relaxed, in rigor, and at various times after activation from rigor by flash photolysis of caged ATP. We used Fourier analysis of images of cross sections to obtain an average view of the muscle structure, and correspondence analysis to extract information about individual crossbridge shapes. The crossbridge structure changes dramatically between relaxed, rigor, and with time after ATP release. In relaxed muscle, most crossbridges are detached. In rigor, all are attached and have a characteristic asymmetric shape that shows strong left-handed curvature when viewed from the M-line towards the Z-line. Immediately after ATP release, before significant force has developed (20 ms) the homogeneous rigor population is replaced by a much more diverse collection of crossbridge shapes. Over the next few hundred milliseconds, the proportion of attached crossbridges changes little, but the distribution of the crossbridges among different structural classes continues to evolve. Some forms of attached crossbridge (presumably weakly attached) increase at early times when tension is low. The proportion of several other attached non-rigor crossbridge shapes increases in parallel with the development of active tension. The results lend strong support to models of muscle contraction that have attributed force generation to structural changes in attached crossbridges.
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Affiliation(s)
- K Hirose
- Department of Cell and Developmental Biology, University of Pennsylvania, Philadelphia 19104-6058
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