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Hojjatian A, Taylor DW, Daneshparvar N, Fagnant PM, Trybus KM, Taylor KA. Double-headed binding of myosin II to F-actin shows the effect of strain on head structure. J Struct Biol 2023; 215:107995. [PMID: 37414375 PMCID: PMC10544818 DOI: 10.1016/j.jsb.2023.107995] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2022] [Revised: 06/25/2023] [Accepted: 07/03/2023] [Indexed: 07/08/2023]
Abstract
Force production in muscle is achieved through the interaction of myosin and actin. Strong binding states in active muscle are associated with Mg·ADP bound to the active site; release of Mg·ADP allows rebinding of ATP and dissociation from actin. Thus, Mg·ADP binding is positioned for adaptation as a force sensor. Mechanical loads on the lever arm can affect the ability of myosin to release Mg·ADP but exactly how this is done is poorly defined. Here we use F-actin decorated with double-headed smooth muscle myosin fragments in the presence of Mg·ADP to visualize the effect of internally supplied tension on the paired lever arms using cryoEM. The interaction of the paired heads with two adjacent actin subunits is predicted to place one lever arm under positive and the other under negative strain. The converter domain is believed to be the most flexible domain within myosin head. Our results, instead, point to the segment of heavy chain between the essential and regulatory light chains as the location of the largest structural change. Moreover, our results suggest no large changes in the myosin coiled coil tail as the locus of strain relief when both heads bind F-actin. The method would be adaptable to double-headed members of the myosin family. We anticipate that the study of actin-myosin interaction using double-headed fragments enables visualization of domains that are typically noisy in decoration with single-headed fragments.
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Affiliation(s)
- Alimohammad Hojjatian
- Inst. of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, United States
| | - Dianne W Taylor
- Inst. of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, United States
| | - Nadia Daneshparvar
- Inst. of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, United States
| | - Patricia M Fagnant
- Dept of Molecular Physiology & Biophysics, University of Vermont College of Medicine, Burlington, VT 05405, United States
| | - Kathleen M Trybus
- Dept of Molecular Physiology & Biophysics, University of Vermont College of Medicine, Burlington, VT 05405, United States
| | - Kenneth A Taylor
- Inst. of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, United States.
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2
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Suzuki M, Mogami G, Ohsugi H, Watanabe T, Matubayasi N. Physical driving force of actomyosin motility based on the hydration effect. Cytoskeleton (Hoboken) 2017; 74:512-527. [PMID: 29087038 DOI: 10.1002/cm.21417] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Revised: 10/24/2017] [Accepted: 10/25/2017] [Indexed: 01/20/2023]
Abstract
We propose a driving force hypothesis based on previous thermodynamics, kinetics and structural data as well as additional experiments and calculations presented here on water-related phenomena in the actomyosin systems. Although Szent-Györgyi pointed out the importance of water in muscle contraction in 1951, few studies have focused on the water science of muscle because of the difficulty of analyzing hydration properties of the muscle proteins, actin, and myosin. The thermodynamics and energetics of muscle contraction are linked to the water-mediated regulation of protein-ligand and protein-protein interactions along with structural changes in protein molecules. In this study, we assume the following two points: (1) the periodic electric field distribution along an actin filament (F-actin) is unidirectionally modified upon binding of myosin subfragment 1 (M or myosin S1) with ADP and inorganic phosphate Pi (M.ADP.Pi complex) and (2) the solvation free energy of myosin S1 depends on the external electric field strength and the solvation free energy of myosin S1 in close proximity to F-actin can become the potential force to drive myosin S1 along F-actin. The first assumption is supported by integration of experimental reports. The second assumption is supported by model calculations utilizing molecular dynamics (MD) simulation to determine solvation free energies of a small organic molecule and two small proteins. MD simulations utilize the energy representation method (ER) and the roughly proportional relationship between the solvation free energy and the solvent-accessible surface area (SASA) of the protein. The estimated driving force acting on myosin S1 is as high as several piconewtons (pN), which is consistent with the experimentally observed force.
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Affiliation(s)
- Makoto Suzuki
- Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, 6-6-07 Aoba, Aramaki, Aoba-ku, Sendai, 980-8579, Japan.,Biological and Molecular Dynamics, Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai, 980-8577, Japan.,Department of Materials Processing, Graduate School of Engineering, Tohoku University, 6-6-02 Aoba, Aramaki, Aoba-ku, Sendai, 980-8579, Japan
| | - George Mogami
- Department of Materials Processing, Graduate School of Engineering, Tohoku University, 6-6-02 Aoba, Aramaki, Aoba-ku, Sendai, 980-8579, Japan
| | - Hideyuki Ohsugi
- Department of Materials Processing, Graduate School of Engineering, Tohoku University, 6-6-02 Aoba, Aramaki, Aoba-ku, Sendai, 980-8579, Japan
| | - Takahiro Watanabe
- Department of Materials Processing, Graduate School of Engineering, Tohoku University, 6-6-02 Aoba, Aramaki, Aoba-ku, Sendai, 980-8579, Japan
| | - Nobuyuki Matubayasi
- Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, 560-8531, Japan.,Elements Strategy Initiative for Catalysts and Batteries, Kyoto University, Katsura, Kyoto, 615-8520, Japan
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3
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Banerjee C, Hu Z, Huang Z, Warrington JA, Taylor DW, Trybus KM, Lowey S, Taylor KA. The structure of the actin-smooth muscle myosin motor domain complex in the rigor state. J Struct Biol 2017; 200:325-333. [PMID: 29038012 DOI: 10.1016/j.jsb.2017.10.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2017] [Revised: 10/11/2017] [Accepted: 10/12/2017] [Indexed: 01/08/2023]
Abstract
Myosin-based motility utilizes catalysis of ATP to drive the relative sliding of F-actin and myosin. The earliest detailed model based on cryo-electron microscopy (cryoEM) and X-ray crystallography postulated that higher actin affinity and lever arm movement were coupled to closure of a feature of the myosin head dubbed the actin-binding cleft. Several studies since then using crystallography of myosin-V and cryoEM structures of F-actin bound myosin-I, -II and -V have provided details of this model. The smooth muscle myosin II interaction with F-actin may differ from those for striated and non-muscle myosin II due in part to different lengths of important surface loops. Here we report a ∼6 Å resolution reconstruction of F-actin decorated with the nucleotide-free recombinant smooth muscle myosin-II motor domain (MD) from images recorded using a direct electron detector. Resolution is highest for F-actin and the actin-myosin interface (3.5-4 Å) and lowest (∼6-7 Å) for those parts of the MD at the highest radius. Atomic models built into the F-actin density are quite comparable to those previously reported for rabbit muscle actin and show density from the bound ADP. The atomic model of the MD, is quite similar to a recently published structure of vertebrate non-muscle myosin II bound to F-actin and a crystal structure of nucleotide free myosin-V. Larger differences are observed when compared to the cryoEM structure of F-actin decorated with rabbit skeletal muscle myosin subfragment 1. The differences suggest less closure of the 50 kDa domain in the actin bound skeletal muscle myosin structure.
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Affiliation(s)
- Chaity Banerjee
- Department of Computer Science, Florida State University, Tallahassee, FL 32306-4530, United States
| | - Zhongjun Hu
- Institute of Molecular Biophysics, Kasha Laboratory, Florida State University, Tallahassee, FL 32306-4380, United States
| | - Zhong Huang
- Institute of Molecular Biophysics, Kasha Laboratory, Florida State University, Tallahassee, FL 32306-4380, United States
| | - J Anthony Warrington
- Institute of Molecular Biophysics, Kasha Laboratory, Florida State University, Tallahassee, FL 32306-4380, United States
| | - Dianne W Taylor
- Institute of Molecular Biophysics, Kasha Laboratory, Florida State University, Tallahassee, FL 32306-4380, United States
| | - Kathleen M Trybus
- Health Science Research Facility 130, 149 Beaumont Avenue, Department of Molecular Physiology & Biophysics, University of Vermont, Burlington, VT 05405, United States
| | - Susan Lowey
- Health Science Research Facility 130, 149 Beaumont Avenue, Department of Molecular Physiology & Biophysics, University of Vermont, Burlington, VT 05405, United States
| | - Kenneth A Taylor
- Institute of Molecular Biophysics, Kasha Laboratory, Florida State University, Tallahassee, FL 32306-4380, United States.
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4
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Flexibility within the heads of muscle myosin-2 molecules. J Mol Biol 2013; 426:894-907. [PMID: 24333017 PMCID: PMC3919154 DOI: 10.1016/j.jmb.2013.11.028] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Revised: 11/25/2013] [Accepted: 11/29/2013] [Indexed: 11/26/2022]
Abstract
We show that negative-stain electron microscopy and image processing of nucleotide-free (apo) striated muscle myosin-2 subfragment-1 (S1), possessing one light chain or both light chains, is capable of resolving significant amounts of structural detail. The overall appearance of the motor and the lever is similar in rabbit, scallop and chicken S1. Projection matching of class averages of the different S1 types to projection views of two different crystal structures of apo S1 shows that all types most commonly closely resemble the appearance of the scallop S1 structure rather than the methylated chicken S1 structure. Methylation of chicken S1 has no effect on the structure of the molecule at this resolution: it too resembles the scallop S1 crystal structure. The lever is found to vary in its angle of attachment to the motor domain, with a hinge point located in the so-called pliant region between the converter and the essential light chain. The chicken S1 crystal structure lies near one end of the range of flexion observed. The Gaussian spread of angles of flexion suggests that flexibility is driven thermally, from which a torsional spring constant of ~ 23 pN·nm/rad2 is estimated on average for all S1 types, similar to myosin-5. This translates to apparent cantilever-type stiffness at the tip of the lever of 0.37 pN/nm. Because this stiffness is lower than recent estimates from myosin-2 heads attached to actin, we suggest that binding to actin leads to an allosteric stiffening of the motor–lever junction. Elasticity of muscle crossbridges is important, but its structural basis is obscure. Muscle myosin heads from rabbit, scallop and chicken share a common structure. The lever domain hinges about its connection with the motor domain. The stiffness of the motor–lever hinge is lower than estimates for crossbridges. Flexibility within the myosin head can be the basis of crossbridge stiffness.
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5
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Li M, Zheng W. All-atom molecular dynamics simulations of actin-myosin interactions: a comparative study of cardiac α myosin, β myosin, and fast skeletal muscle myosin. Biochemistry 2013; 52:8393-405. [PMID: 24224850 DOI: 10.1021/bi4006896] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Myosins are a superfamily of actin-binding motor proteins with significant variations in kinetic properties (such as actin binding affinity) between different isoforms. It remains unknown how such kinetic variations arise from the structural and dynamic tuning of the actin-myosin interface at the amino acid residue level. To address this key issue, we have employed molecular modeling and simulations to investigate, with atomistic details, the isoform dependence of actin-myosin interactions in the rigor state. By combining electron microscopy-based docking with homology modeling, we have constructed three all-atom models for human cardiac α and β and rabbit fast skeletal muscle myosin in complex with three actin subunits in the rigor state. Starting from these models, we have performed extensive all-atom molecular dynamics (MD) simulations (total of 100 ns per system) and then used the MD trajectories to calculate actin-myosin binding free energies with contributions from both electrostatic and nonpolar forces. Our binding calculations are in good agreement with the experimental finding of isoform-dependent differences in actin binding affinity between these myosin isoforms. Such differences are traced to changes in actin-myosin electrostatic interactions (i.e., hydrogen bonds and salt bridges) that are highly dynamic and involve several flexible actin-binding loops. By partitioning the actin-myosin binding free energy to individual myosin residues, we have also identified key myosin residues involved in the actin-myosin interactions, some of which were previously validated experimentally or implicated in cardiomyopathy mutations, and the rest make promising targets for future mutational experiments.
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Affiliation(s)
- Minghui Li
- Physics Department, University at Buffalo , Buffalo, New York 14260, United States
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6
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Behrmann E, Müller M, Penczek PA, Mannherz HG, Manstein DJ, Raunser S. Structure of the rigor actin-tropomyosin-myosin complex. Cell 2012; 150:327-38. [PMID: 22817895 DOI: 10.1016/j.cell.2012.05.037] [Citation(s) in RCA: 267] [Impact Index Per Article: 22.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2012] [Revised: 03/13/2012] [Accepted: 05/20/2012] [Indexed: 01/13/2023]
Abstract
Regulation of myosin and filamentous actin interaction by tropomyosin is a central feature of contractile events in muscle and nonmuscle cells. However, little is known about molecular interactions within the complex and the trajectory of tropomyosin movement between its "open" and "closed" positions on the actin filament. Here, we report the 8 Å resolution structure of the rigor (nucleotide-free) actin-tropomyosin-myosin complex determined by cryo-electron microscopy. The pseudoatomic model of the complex, obtained from fitting crystal structures into the map, defines the large interface involving two adjacent actin monomers and one tropomyosin pseudorepeat per myosin contact. Severe forms of hereditary myopathies are linked to mutations that critically perturb this interface. Myosin binding results in a 23 Å shift of tropomyosin along actin. Complex domain motions occur in myosin, but not in actin. Based on our results, we propose a structural model for the tropomyosin-dependent modulation of myosin binding to actin.
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Affiliation(s)
- Elmar Behrmann
- Department of Physical Biochemistry, Max Planck Institute of Molecular Physiology, 44227 Dortmund, Germany
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7
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Noguchi TQP, Komori T, Umeki N, Demizu N, Ito K, Iwane AH, Tokuraku K, Yanagida T, Uyeda TQP. G146V mutation at the hinge region of actin reveals a myosin class-specific requirement of actin conformations for motility. J Biol Chem 2012; 287:24339-45. [PMID: 22637580 DOI: 10.1074/jbc.m111.321752] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The G146V mutation in actin is dominant lethal in yeast. G146V actin filaments bind cofilin only minimally, presumably because cofilin binding requires the large and small actin domains to twist with respect to one another around the hinge region containing Gly-146, and the mutation inhibits that twisting motion. A number of studies have suggested that force generation by myosin also requires actin filaments to undergo conformational changes. This prompted us to examine the effects of the G146V mutation on myosin motility. When compared with wild-type actin filaments, G146V filaments showed a 78% slower gliding velocity and a 70% smaller stall force on surfaces coated with skeletal heavy meromyosin. In contrast, the G146V mutation had no effect on either gliding velocity or stall force on myosin V surfaces. Kinetic analyses of actin-myosin binding and ATPase activity indicated that the weaker affinity of actin filaments for myosin heads carrying ADP, as well as reduced actin-activated ATPase activity, are the cause of the diminished motility seen with skeletal myosin. Interestingly, the G146V mutation disrupted cooperative binding of myosin II heads to actin filaments. These data suggest that myosin-induced conformational changes in the actin filaments, presumably around the hinge region, are involved in mediating the motility of skeletal myosin but not myosin V and that the specific structural requirements for the actin subunits, and thus the mechanism of motility, differ among myosin classes.
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Affiliation(s)
- Taro Q P Noguchi
- Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Higashi, Tsukuba, Ibaraki 305-8562, Japan.
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8
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Myosin binding surface on actin probed by hydroxyl radical footprinting and site-directed labels. J Mol Biol 2011; 414:204-16. [PMID: 21986200 DOI: 10.1016/j.jmb.2011.09.035] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Revised: 09/09/2011] [Accepted: 09/20/2011] [Indexed: 11/22/2022]
Abstract
Actin and myosin are the two main proteins required for cell motility and muscle contraction. The structure of their strongly bound complex-rigor state-is a key for delineating the functional mechanism of actomyosin motor. Current knowledge of that complex is based on models obtained from the docking of known atomic structures of actin and myosin subfragment 1 (S1; the head and neck region of myosin) into low-resolution electron microscopy electron density maps, which precludes atomic- or side-chain-level information. Here, we use radiolytic protein footprinting for global mapping of sites across the actin molecules that are impacted directly or allosterically by myosin binding to actin filaments. Fluorescence and electron paramagnetic resonance spectroscopies and cysteine actin mutants are used for independent, residue-specific probing of S1 effects on two structural elements of actin. We identify actin residue candidates involved in S1 binding and provide experimental evidence to discriminate between the regions of hydrophobic and electrostatic interactions. Focusing on the role of the DNase I binding loop (D-loop) and the W-loop residues of actin in their interactions with S1, we found that the emission properties of acrylodan and the mobility of electron paramagnetic resonance spin labels attached to cysteine mutants of these residues change strongly and in a residue-specific manner upon S1 binding, consistent with the recently proposed direct contacts of these loops with S1. As documented in this study, the direct and indirect changes on actin induced by myosin are more extensive than known until now and attest to the importance of actin dynamics to actomyosin function.
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9
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Prochniewicz E, Pierre A, McCullough BR, Chin HF, Cao W, Saunders LP, Thomas DD, De La Cruz EM. Actin filament dynamics in the actomyosin VI complex is regulated allosterically by calcium-calmodulin light chain. J Mol Biol 2011; 413:584-92. [PMID: 21910998 DOI: 10.1016/j.jmb.2011.08.058] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2011] [Revised: 08/05/2011] [Accepted: 08/31/2011] [Indexed: 11/28/2022]
Abstract
The contractile and enzymatic activities of myosin VI are regulated by calcium binding to associated calmodulin (CaM) light chains. We have used transient phosphorescence anisotropy to monitor the microsecond rotational dynamics of erythrosin-iodoacetamide-labeled actin with strongly bound myosin VI (MVI) and to evaluate the effect of MVI-bound CaM light chain on actin filament dynamics. MVI binding lowers the amplitude but accelerates actin filament microsecond dynamics in a Ca(2+)- and CaM-dependent manner, as indicated from an increase in the final anisotropy and a decrease in the correlation time of transient phosphorescence anisotropy decays. MVI with bound apo-CaM or Ca(2+)-CaM weakly affects actin filament microsecond dynamics, relative to other myosins (e.g., muscle myosin II and myosin Va). CaM dissociation from bound MVI damps filament rotational dynamics (i.e., increases the torsional rigidity), such that the perturbation is comparable to that induced by other characterized myosins. Analysis of individual actin filament shape fluctuations imaged by fluorescence microscopy reveals a correlated effect on filament bending mechanics. These data support a model in which Ca(2+)-dependent CaM binding to the IQ domain of MVI is linked to an allosteric reorganization of the actin binding site(s), which alters the structural dynamics and the mechanical rigidity of actin filaments. Such modulation of filament dynamics may contribute to the Ca(2)(+)- and CaM-dependent regulation of myosin VI motility and ATP utilization.
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Affiliation(s)
- Ewa Prochniewicz
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
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10
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Prochniewicz E, Chin HF, Henn A, Hannemann DE, Olivares AO, Thomas DD, De La Cruz EM. Myosin isoform determines the conformational dynamics and cooperativity of actin filaments in the strongly bound actomyosin complex. J Mol Biol 2009; 396:501-9. [PMID: 19962990 DOI: 10.1016/j.jmb.2009.11.063] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2009] [Revised: 10/06/2009] [Accepted: 11/27/2009] [Indexed: 10/20/2022]
Abstract
We used transient phosphorescence anisotropy to detect the microsecond rotational dynamics of erythrosin-iodoacetamide-labeled actin strongly bound to single-headed fragments of muscle myosin subfragment 1 (S1) and non-muscle myosin V (MV). The conformational dynamics of actin filaments in solution are markedly influenced by the isoform of bound myosin. Both myosins increase the final anisotropy of actin at substoichiometric binding densities, indicating long-range, non-nearest neighbor cooperative restriction of filament rotational dynamics amplitude, but the cooperative unit is larger with MV than with muscle S1. Both myosin isoforms also cooperatively affect the actin filament rotational correlation time, but with opposite effects: muscle S1 decreases rates of intrafilament torsional motion, while binding of MV increases the rates of motion. The cooperative effects on the rates of intrafilament motions correlate with the kinetics of myosin binding to actin filaments such that MV binds more rapidly and muscle myosin binds more slowly to partially decorated filaments than to bare filaments. The two isoforms also differ in their effects on the phosphorescence lifetime of the actin-bound erythrosin iodoacetamide: while muscle S1 increases the lifetime, suggesting decreased aqueous exposure of the probe, MV does not induce a significant change. We conclude that the dynamics and structure of actin in the strongly bound actomyosin complex are determined by the isoform of the bound myosin in a manner likely to accommodate the diverse functional roles of actomyosin in muscle and non-muscle cells.
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Affiliation(s)
- Ewa Prochniewicz
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
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11
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Thomas DD, Kast D, Korman VL. Site-directed spectroscopic probes of actomyosin structural dynamics. Annu Rev Biophys 2009; 38:347-69. [PMID: 19416073 DOI: 10.1146/annurev.biophys.35.040405.102118] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Spectroscopy of myosin and actin has entered a golden age. High-resolution crystal structures of isolated actin and myosin have been used to construct detailed models for the dynamic actomyosin interactions that move muscle. Improved protein mutagenesis and expression technologies have facilitated site-directed labeling with fluorescent and spin probes. Spectroscopic instrumentation has achieved impressive advances in sensitivity and resolution. Here we highlight the contributions of site-directed spectroscopic probes to understanding the structural dynamics of myosin II and its actin complexes in solution and muscle fibers. We emphasize studies that probe directly the movements of structural elements within the myosin catalytic and light-chain domains, and changes in the dynamics of both actin and myosin due to their alternating strong and weak interactions in the ATPase cycle. A moving picture emerges in which single biochemical states produce multiple structural states, and transitions between states of order and dynamic disorder power the actomyosin engine.
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Affiliation(s)
- David D Thomas
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA.
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12
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Littlefield KP, Ward AB, Chappie JS, Reedy MK, Bernstein SI, Milligan RA, Reedy MC. Similarities and differences between frozen-hydrated, rigor acto-S1 complexes of insect flight and chicken skeletal muscles. J Mol Biol 2008; 381:519-28. [PMID: 18588896 DOI: 10.1016/j.jmb.2008.06.029] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2008] [Revised: 06/06/2008] [Accepted: 06/11/2008] [Indexed: 11/25/2022]
Abstract
The structure and function of myosin crossbridges in asynchronous insect flight muscle (IFM) have been elucidated in situ using multiple approaches. These include generating "atomic" models of myosin in multiple contractile states by rebuilding the crystal structure of chicken subfragment 1 (S1) to fit IFM crossbridges in lower-resolution electron microscopy tomograms and by "mapping" the functional effects of genetically substituted, isoform-specific domains, including the converter domain, in chimeric IFM myosin to sequences in the crystal structure of chicken S1. We prepared helical reconstructions (approximately 25 A resolution) to compare the structural characteristics of nucleotide-free myosin0 S1 bound to actin (acto-S1) isolated from chicken skeletal muscle (CSk) and the flight muscles of Lethocerus (Leth) wild-type Drosophila (wt Dros) and a Drosophila chimera (IFI-EC) wherein the converter domain of the indirect flight muscle myosin isoform has been replaced by the embryonic skeletal myosin converter domain. Superimposition of the maps of the frozen-hydrated acto-S1 complexes shows that differences between CSk and IFM S1 are limited to the azimuthal curvature of the lever arm: the regulatory light-chain (RLC) region of chicken skeletal S1 bends clockwise (as seen from the pointed end of actin) while those of IFM S1 project in a straight radial direction. All the IFM S1s are essentially identical other than some variation in the azimuthal spread of density in the RLC region. This spread is most pronounced in the IFI-EC S1, consistent with proposals that the embryonic converter domain increases the compliance of the IFM lever arm affecting the function of the myosin motor. These are the first unconstrained models of IFM S1 bound to actin and the first direct comparison of the vertebrate and invertebrate skeletal myosin II classes, the latter for which, data on the structure of discrete acto-S1 complexes, are not readily available.
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Lowey S, Lesko LM, Rovner AS, Hodges AR, White SL, Low RB, Rincon M, Gulick J, Robbins J. Functional effects of the hypertrophic cardiomyopathy R403Q mutation are different in an alpha- or beta-myosin heavy chain backbone. J Biol Chem 2008; 283:20579-89. [PMID: 18480046 DOI: 10.1074/jbc.m800554200] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The R403Q mutation in the beta-myosin heavy chain (MHC) was the first mutation to be linked to familial hypertrophic cardiomyopathy (FHC), a primary disease of heart muscle. The initial studies with R403Q myosin, isolated from biopsies of patients, showed a large decrease in myosin motor function, leading to the hypothesis that hypertrophy was a compensatory response. The introduction of the mouse model for FHC (the mouse expresses predominantly alpha-MHC as opposed to the beta-isoform in larger mammals) created a new paradigm for FHC based on finding enhanced motor function for R403Q alpha-MHC. To help resolve these conflicting mechanisms, we used a transgenic mouse model in which the endogenous alpha-MHC was largely replaced with transgenically encoded beta-MHC. A His(6) tag was cloned at the N terminus of the alpha-and beta-MHC to facilitate protein isolation by Ni(2+)-chelating chromatography. Characterization of the R403Q alpha-MHC by the in vitro motility assay showed a 30-40% increase in actin filament velocity compared with wild type, consistent with published studies. In contrast, the R403Q mutation in a beta-MHC backbone showed no enhancement in velocity. Cleavage of the His-tagged myosin by chymotrypsin made it possible to isolate homogeneous myosin subfragment 1 (S1), uncontaminated by endogenous myosin. We find that the actin-activated MgATPase activity for R403Q alpha-S1 is approximately 30% higher than for wild type, whereas the enzymatic activity for R403Q beta-S1 is reduced by approximately 10%. Thus, the functional consequences of the mutation are fundamentally changed depending upon the context of the cardiac MHC isoform.
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Affiliation(s)
- Susan Lowey
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405, USA.
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14
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Volkmann N, Lui H, Hazelwood L, Trybus KM, Lowey S, Hanein D. The R403Q myosin mutation implicated in familial hypertrophic cardiomyopathy causes disorder at the actomyosin interface. PLoS One 2007; 2:e1123. [PMID: 17987111 PMCID: PMC2040505 DOI: 10.1371/journal.pone.0001123] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2007] [Accepted: 10/04/2007] [Indexed: 11/29/2022] Open
Abstract
Background Mutations in virtually all of the proteins comprising the cardiac muscle sarcomere have been implicated in causing Familial Hypertrophic Cardiomyopathy (FHC). Mutations in the β-myosin heavy chain (MHC) remain among the most common causes of FHC, with the widely studied R403Q mutation resulting in an especially severe clinical prognosis. In vitro functional studies of cardiac myosin containing the R403Q mutation have revealed significant changes in enzymatic and mechanical properties compared to wild-type myosin. It has been proposed that these molecular changes must trigger events that ultimately lead to the clinical phenotype. Principal Findings Here we examine the structural consequences of the R403Q mutation in a recombinant smooth muscle myosin subfragment (S1), whose kinetic features have much in common with slow β-MHC. We obtained three-dimensional reconstructions of wild-type and R403Q smooth muscle S1 bound to actin filaments in the presence (ADP) and absence (apo) of nucleotide by electron cryomicroscopy and image analysis. We observed that the mutant S1 was attached to actin at highly variable angles compared to wild-type reconstructions, suggesting a severe disruption of the actin-myosin interaction at the interface. Significance These results provide structural evidence that disarray at the molecular level may be linked to the histopathological myocyte disarray characteristic of the diseased state.
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Affiliation(s)
- Niels Volkmann
- Burnham Institute for Medical Research, La Jolla, California, United States of America
| | - HongJun Lui
- Burnham Institute for Medical Research, La Jolla, California, United States of America
| | - Larnele Hazelwood
- Burnham Institute for Medical Research, La Jolla, California, United States of America
| | - Kathleen M. Trybus
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont, United States of America
| | - Susan Lowey
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont, United States of America
- * To whom correspondence should be addressed. E-mail: (SL); (DH)
| | - Dorit Hanein
- Burnham Institute for Medical Research, La Jolla, California, United States of America
- * To whom correspondence should be addressed. E-mail: (SL); (DH)
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15
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Trybus KM, Gushchin MI, Lui H, Hazelwood L, Krementsova EB, Volkmann N, Hanein D. Effect of calcium on calmodulin bound to the IQ motifs of myosin V. J Biol Chem 2007; 282:23316-25. [PMID: 17562702 DOI: 10.1074/jbc.m701636200] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The long neck of unconventional myosin V is composed of six tandem "IQ motifs," which are fully occupied by calmodulin (CaM) in the absence of calcium. Calcium regulates the activity, the folded-to-extended conformational transition, and the processive run length of myosin V, and thus, it is important to understand how calcium affects CaM binding to the IQ motifs. Here we used electron cryomicroscopy together with computer-based docking of crystal structures into three-dimensional reconstructions of actin decorated with a motor domain-two IQ complex to provide an atomic model of myosin V in the presence of calcium. Calcium causes a major rearrangement of the bound CaMs, dissociation of CaM bound to IQ motif 2, and propagated changes in the motor domain. Tryptophan fluorescence spectroscopy showed that calcium-CaM binds to IQ motifs 1, 3, and 5 in a different conformation than apoCaM. Proteolytic cleavage was consistent with CaM preferentially dissociating from the second IQ motif. The enzymatic and mechanical functions of myosin V can, therefore, be modulated both by calcium-dependent conformational changes of bound CaM as well as by CaM dissociation.
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Affiliation(s)
- Kathleen M Trybus
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont 05405, USA.
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16
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Iwamoto H, Oiwa K, Kovács M, Sellers JR, Suzuki T, Wakayama J, Tamura T, Yagi N, Fujisawa T. Diversity of structural behavior in vertebrate conventional myosins complexed with actin. J Mol Biol 2007; 369:249-64. [PMID: 17433365 PMCID: PMC1997293 DOI: 10.1016/j.jmb.2007.03.031] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2006] [Revised: 03/12/2007] [Accepted: 03/13/2007] [Indexed: 11/28/2022]
Abstract
Low-resolution three-dimensional structures of acto-myosin subfragment-1 (S1) complexes were retrieved from X-ray fiber diffraction patterns, recorded either in the presence or absence of ADP. The S1 was obtained from various myosin-II isoforms from vertebrates, including rabbit fast-skeletal and cardiac, chicken smooth and human non-muscle IIA and IIB species, and was diffused into an array of overstretched, skinned skeletal muscle fibers. The S1 attached to the exposed actin filaments according to their helical symmetry. Upon addition of ADP, the diffraction patterns from acto-S1 showed an increasing magnitude of response in the order as listed above, with features of a lateral compression of the whole diffraction pattern (indicative of increased radius of the acto-S1 complex) and an enhancement of the fifth layer-line reflection. The structure retrieval indicates that these changes are mainly due to the swing of the light chain (LC) domain in the direction consistent with the cryo-electron microscopic results. In the non-muscle isoforms, the swing is large enough to affect the manner of quasi-crystal packing of the S1-decorated actin filaments and their lattice dimension, with a small change in the twist of actin filaments. Variations also exist in the behavior of the 50K-cleft, which apparently opens upon addition of ADP to the non-muscle isoforms but not to other isoforms. The fast-skeletal S1 remains as the only isoform that does not clearly exhibit either of the structural changes. The results indicate that the "conventional" myosin-II isoforms exhibit a wide variety of structural behavior, possibly depending on their functions and/or the history of molecular evolution.
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Affiliation(s)
- Hiroyuki Iwamoto
- Research and Utilization Division, SPring-8, Japan Synchrotron Radiation Research Institute, Hyogo 679-6198, Japan.
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17
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Miller BM, Bloemink MJ, Nyitrai M, Bernstein SI, Geeves MA. A variable domain near the ATP-binding site in Drosophila muscle myosin is part of the communication pathway between the nucleotide and actin-binding sites. J Mol Biol 2007; 368:1051-66. [PMID: 17379245 PMCID: PMC2034518 DOI: 10.1016/j.jmb.2007.02.042] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2006] [Revised: 02/12/2007] [Accepted: 02/13/2007] [Indexed: 11/16/2022]
Abstract
Drosophila expresses several muscle myosin isoforms from a single gene by alternatively splicing six of the 19 exons. Here we investigate exon 7, which codes for a region in the upper 50 kDa domain near the nucleotide-binding pocket. This region is of interest because it is also the place where a large insert is found in myosin VI and where several cardiomyopathy mutations have been identified in human cardiac myosin. We expressed and purified chimeric muscle myosins from Drosophila, each varying at exon 7. Two chimeras exchanged the entire exon 7 domain between the indirect flight muscle (IFI, normally containing exon 7d) and embryonic body wall muscle (EMB, normally containing exon 7a) isoforms to create IFI-7a and EMB-7d. The second two chimeras replaced each half of the exon 7a domain in EMB with the corresponding portion of exon 7d to create EMB-7a/7d and EMB-7d/7a. Transient kinetic studies of the motor domain from these myosin isoforms revealed changes in several kinetic parameters between the IFI or EMB isoforms and the chimeras. Of significance were changes in nucleotide binding, which differed in the presence and absence of actin, consistent with a model in which the exon 7 domain is part of the communication pathway between the nucleotide and actin-binding sites. Homology models of the structures suggest how the exon 7 domain might modulate this pathway.
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Affiliation(s)
- Becky M Miller
- Department of Biology and Molecular Biology Institute, San Diego State University, San Diego, CA 92182-4614, USA
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18
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Yu H, Ma L, Yang Y, Cui Q. Mechanochemical coupling in the myosin motor domain. II. Analysis of critical residues. PLoS Comput Biol 2007; 3:e23. [PMID: 17305418 PMCID: PMC1800309 DOI: 10.1371/journal.pcbi.0030023] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2006] [Accepted: 12/21/2006] [Indexed: 12/02/2022] Open
Abstract
An important challenge in the analysis of mechanochemical coupling in molecular motors is to identify residues that dictate the tight coupling between the chemical site and distant structural rearrangements. In this work, a systematic attempt is made to tackle this issue for the conventional myosin. By judiciously combining a range of computational techniques with different approximations and strength, which include targeted molecular dynamics, normal mode analysis, and statistical coupling analysis, we are able to identify a set of important residues and propose their relevant function during the recovery stroke of myosin. These analyses also allowed us to make connections with previous experimental and computational studies in a critical manner. The behavior of the widely used reporter residue, Trp501, in the simulations confirms the concern that its fluorescence does not simply reflect the relay loop conformation or active-site open/close but depends subtly on its microenvironment. The findings in the targeted molecular dynamics and a previous minimum energy path analysis of the recovery stroke have been compared and analyzed, which emphasized the difference and complementarity of the two approaches. In conjunction with our previous studies, the current set of investigations suggest that the modulation of structural flexibility at both the local (e.g., active-site) and domain scales with strategically placed "hotspot" residues and phosphate chemistry is likely the general feature for mechanochemical coupling in many molecular motors. The fundamental strategies of examining both collective and local changes and combining physically motivated methods and informatics-driven techniques are expected to be valuable to the study of other molecular motors and allosteric systems in general.
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Affiliation(s)
- Haibo Yu
- Department of Chemistry, University of Wisconsin, Madison, Wisconsin, United States of America
- Theoretical Chemistry Institute, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Liang Ma
- Department of Chemistry, University of Wisconsin, Madison, Wisconsin, United States of America
- Theoretical Chemistry Institute, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Yang Yang
- Department of Chemistry, University of Wisconsin, Madison, Wisconsin, United States of America
- Theoretical Chemistry Institute, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Qiang Cui
- Department of Chemistry, University of Wisconsin, Madison, Wisconsin, United States of America
- Theoretical Chemistry Institute, University of Wisconsin, Madison, Wisconsin, United States of America
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19
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Naber N, Purcell TJ, Pate E, Cooke R. Dynamics of the nucleotide pocket of myosin measured by spin-labeled nucleotides. Biophys J 2006; 92:172-84. [PMID: 17028139 PMCID: PMC1697850 DOI: 10.1529/biophysj.106.090035] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have used electron paramagnetic probes attached to the ribose of ATP (SL-ATP) to monitor conformational changes in the nucleotide pocket of myosin. Spectra for analogs bound to myosin in the absence of actin showed a high degree of immobilization, indicating a closed nucleotide pocket. In the Actin.Myosin.SL-AMPPNP, Actin.Myosin.SL-ADP.BeF(3), and Actin.Myosin.SL-ADP.AlF(4) complexes, which mimic weakly binding states near the beginning of the power stroke, the nucleotide pocket remained closed. The spectra of the strongly bound Actin.Myosin.SL-ADP complex consisted of two components, one similar to the closed pocket and one with increased probe mobility, indicating a more open pocket, The temperature dependence of the spectra showed that the two conformations of the nucleotide pocket were in equilibrium, with the open conformation more favorable at higher temperatures. These results, which show that opening of the pocket occurs only in the strongly bound states, appear reasonable, as this would tend to keep ADP bound until the end of the power stroke. This conclusion also suggests that force is initially generated by a myosin with a closed nucleotide pocket.
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Affiliation(s)
- Nariman Naber
- Department of Biochemistry and Biophysics, University of California, San Francisco, California 94158, USA.
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20
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Schmitt JP, Debold EP, Ahmad F, Armstrong A, Frederico A, Conner DA, Mende U, Lohse MJ, Warshaw D, Seidman CE, Seidman JG. Cardiac myosin missense mutations cause dilated cardiomyopathy in mouse models and depress molecular motor function. Proc Natl Acad Sci U S A 2006; 103:14525-30. [PMID: 16983074 PMCID: PMC1599993 DOI: 10.1073/pnas.0606383103] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Dilated cardiomyopathy (DCM) leads to heart failure, a leading cause of death in industrialized nations. Approximately 30% of DCM cases are genetic in origin, with some resulting from point mutations in cardiac myosin, the molecular motor of the heart. The effects of these mutations on myosin's molecular mechanics have not been determined. We have engineered two murine models characterizing the physiological, cellular, and molecular effects of DCM-causing missense mutations (S532P and F764L) in the alpha-cardiac myosin heavy chain and compared them with WT mice. Mutant mice developed morphological and functional characteristics of DCM consistent with the human phenotypes. Contractile function of isolated myocytes was depressed and preceded left ventricular dilation and reduced fractional shortening. In an in vitro motility assay, both mutant cardiac myosins exhibited a reduced ability to translocate actin (V(actin)) but had similar force-generating capacities. Actin-activated ATPase activities were also reduced. Single-molecule laser trap experiments revealed that the lower V(actin) in the S532P mutant was due to a reduced ability of the motor to generate a step displacement and an alteration of the kinetics of its chemomechanical cycle. These results suggest that the depressed molecular function in cardiac myosin may initiate the events that cause the heart to remodel and become pathologically dilated.
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Affiliation(s)
- Joachim P. Schmitt
- *Department of Genetics and Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115
- Institute of Pharmacology and Toxicology, University of Würzburg, 97087 Würzburg, Germany; and
| | - Edward P. Debold
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405
| | - Ferhaan Ahmad
- *Department of Genetics and Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115
| | - Amy Armstrong
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405
| | - Andrea Frederico
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405
| | - David A. Conner
- *Department of Genetics and Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115
| | | | - Martin J. Lohse
- Institute of Pharmacology and Toxicology, University of Würzburg, 97087 Würzburg, Germany; and
| | - David Warshaw
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405
| | - Christine E. Seidman
- *Department of Genetics and Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115
- Cardiovascular Division and
- **Howard Hughes Medical Institute, Brigham and Women's Hospital, Boston, MA 02115
| | - J. G. Seidman
- *Department of Genetics and Howard Hughes Medical Institute, Harvard Medical School, Boston, MA 02115
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21
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Guo B, Guilford WH. Mechanics of actomyosin bonds in different nucleotide states are tuned to muscle contraction. Proc Natl Acad Sci U S A 2006; 103:9844-9. [PMID: 16785439 PMCID: PMC1502541 DOI: 10.1073/pnas.0601255103] [Citation(s) in RCA: 195] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Muscle contraction and many other cell movements are driven by cyclic interactions between actin filaments and the motor enzyme myosin. Conformational changes in the actin-myosin binding interface occur in concert with the binding of ATP, binding to actin, and loss of hydrolytic by-products, but the effects of these conformational changes on the strength of the actomyosin bond are unknown. The force-dependent kinetics of the actomyosin bond may be particularly important at high loads, where myosin may detach from actin before achieving its full power stroke. Here we show that over a physiological range of rapidly applied loads, actomyosin behaves as a "catch" bond, characterized by increasing lifetimes with increasing loads up to a maximum at approximately 6 pN. Surprisingly, we found that the myosin-ADP bond is possessed of longer lifetimes under load than rigor bonds, although the load at which bond lifetime is maximal remains unchanged. We also found that actomyosin bond lifetime is ultimately dependent not only on load, but loading history as well. These data suggest a complex relationship between the rate of actomyosin dissociation and muscle force and shortening velocity. The 6-pN load for maximum bond lifetime is near the force generated by a single myosin molecule during isometric contraction. This raises the possibility that all catch bonds between load-bearing molecules are "mechanokinetically" tuned to their physiological environment.
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Affiliation(s)
- Bin Guo
- Department of Biomedical Engineering, University of Virginia, Box 800759, Charlottesville, VA 22908
| | - William H. Guilford
- Department of Biomedical Engineering, University of Virginia, Box 800759, Charlottesville, VA 22908
- To whom correspondence should be addressed. E-mail:
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22
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Miller BM, Zhang S, Suggs JA, Swank DM, Littlefield KP, Knowles AF, Bernstein SI. An alternative domain near the nucleotide-binding site of Drosophila muscle myosin affects ATPase kinetics. J Mol Biol 2005; 353:14-25. [PMID: 16154586 DOI: 10.1016/j.jmb.2005.08.012] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2005] [Revised: 08/05/2005] [Accepted: 08/10/2005] [Indexed: 11/29/2022]
Abstract
In Drosophila melanogaster expression of muscle myosin heavy chain isoforms occurs by alternative splicing of transcripts from a single gene. The exon 7 domain is one of four variable regions in the catalytic head and is located near the nucleotide-binding site. To ascribe a functional role to this domain, we created two chimeric myosin isoforms (indirect flight isoform-exon 7a and embryonic-exon 7d) that differ from the native indirect flight muscle and embryonic body-wall muscle isoforms only in the exon 7 region. Germline transformation and subsequent expression of the chimeric myosins in the indirect flight muscle of myosin-null Drosophila allowed us to purify the myosin for in vitro studies and to assess in vivo structure and function of transgenic muscles. Intriguingly, in vitro experiments show the exon 7 domain modulates myosin ATPase activity but has no effect on actin filament velocity, a novel result compared to similar studies with other Drosophila variable exons. Transgenic flies expressing the indirect flight isoform-exon 7a have normal indirect flight muscle structure, and flight and jump ability. However, expression of the embryonic-exon 7d chimeric isoform yields flightless flies that show improvements in both the structural stability of the indirect flight muscle and in locomotor abilities as compared to flies expressing the embryonic isoform. Overall, our results suggest the exon 7 domain participates in the regulation of the attachment of myosin to actin in order to fine-tune the physiological properties of Drosophila myosin isoforms.
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Affiliation(s)
- Becky M Miller
- Department of Biology and Molecular Biology Institute, San Diego State University, San Diego, CA 92182-4614, USA
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23
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Korman VL, Anderson SEB, Prochniewicz E, Titus MA, Thomas DD. Structural dynamics of the actin-myosin interface by site-directed spectroscopy. J Mol Biol 2005; 356:1107-17. [PMID: 16406406 DOI: 10.1016/j.jmb.2005.10.024] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2005] [Revised: 10/07/2005] [Accepted: 10/11/2005] [Indexed: 11/19/2022]
Abstract
We have used site-directed spin and fluorescence labeling to test molecular models of the actin-myosin interface. Force is generated when the actin-myosin complex undergoes a transition from a disordered weak-binding state to an ordered strong-binding state. Actomyosin interface models, in which residues are classified as contributing to either weak or strong binding, have been derived by fitting individual crystallographic structures of actin and myosin into actomyosin cryo-EM maps. Our goal is to test these models using site-directed spectroscopic probes on actin and myosin. Starting with Cys-lite constructs of both yeast actin (ActC) and the Dictyostelium myosin II motor domain (S1dC), site-directed labeling (SDL) mutants were generated by mutating residues to Cys in the proposed weak and strong-binding interfaces. This report focuses on the effects of forming the strong-binding complex on four SDL mutants, two located in the proposed weak-binding interface (ActC5 and S1dC619) and two located in the proposed strong-binding interface (ActC345 and S1dC401). Neither the mutations nor labeling prevented strong actomyosin binding or actin-activation of myosin ATPase. Formation of the strong-binding complex resulted in decreased spin and fluorescence probe mobility at all sites, but both myosin-bound probes showed remarkably high mobility even after complex formation. Complex formation decreased solvent accessibility for both actin-bound probes, but increased it for the myosin-bound probes. These results are not consistent with a simple model in which there are discrete weak and strong interfaces, with only the strong interface forming under strong-binding conditions, nor are they consistent with a model in which surface residues become rigid and inaccessible upon complex formation. We conclude that all four of these residues are involved in the strong actin-myosin interface, but this interface is remarkably dynamic, especially on the surface of myosin.
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Affiliation(s)
- Vicci L Korman
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
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24
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Volkmann N, Liu H, Hazelwood L, Krementsova EB, Lowey S, Trybus KM, Hanein D. The structural basis of myosin V processive movement as revealed by electron cryomicroscopy. Mol Cell 2005; 19:595-605. [PMID: 16137617 DOI: 10.1016/j.molcel.2005.07.015] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2005] [Revised: 06/20/2005] [Accepted: 07/14/2005] [Indexed: 11/24/2022]
Abstract
The processive motor myosin V has a relatively high affinity for actin in the presence of ATP and, thus, offers the unique opportunity to visualize some of the weaker, hitherto inaccessible, actin bound states of the ATPase cycle. Here, electron cryomicroscopy together with computer-based docking of crystal structures into three-dimensional (3D) reconstructions provide the atomic models of myosin V in both weak and strong actin bound states. One structure shows that ATP binding opens the long cleft dividing the actin binding region of the motor domain, thus destroying the strong binding actomyosin interface while rearranging loop 2 as a tether. Nucleotide analogs showed a second new state in which the lever arm points upward, in a prepower-stroke configuration (lever arm up) bound to actin before phosphate release. Our findings reveal how the structural elements of myosin V work together to allow myosin V to step along actin for multiple ATPase cycles without dissociating.
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Affiliation(s)
- Niels Volkmann
- The Program of Cell Adhesion, The Burnham Institute, La Jolla, California 92037, USA
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25
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Fabiola F, Chapman MS. Fitting of high-resolution structures into electron microscopy reconstruction images. Structure 2005; 13:389-400. [PMID: 15766540 DOI: 10.1016/j.str.2005.01.007] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2004] [Revised: 01/19/2005] [Accepted: 01/20/2005] [Indexed: 11/19/2022]
Abstract
Dynamic macromolecular assemblies, such as ribosomes, viruses, and muscle protein complexes, are often more amenable to visualization by electron microscopy than by high-resolution X-ray crystallography or NMR. When high-resolution structures of component structures are available, it is possible to build an atomic model that gives information about the molecular interactions at greater detail than the experimental resolution, due to constraints of modeling placed upon the interpretation. There are now several competing computational methods to search systematically for orientations and positions of components that match the experimental image density, and continuing developments will be reviewed. Attention is now also moving toward the related task of optimization, with flexible and/or multifragment models and sometimes with stereochemically restrained refinement methods. This paper will review the various approaches and describe advances in the authors' methods and applications of real-space refinement.
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Affiliation(s)
- Felcy Fabiola
- Institute of Molecular Biophysics, Florida State University, Tallahassee, Florida 32306, USA
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26
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Robertson CI, Gaffney DP, Chrin LR, Berger CL. Structural rearrangements in the active site of smooth-muscle myosin. Biophys J 2005; 89:1882-92. [PMID: 15951390 PMCID: PMC1366691 DOI: 10.1529/biophysj.105.059840] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Structural rearrangements of the myosin upper-50 kD subdomain are thought to play a key role in coordinating actin binding with nucleotide hydrolysis during the myosin ATPase cycle. Such rearrangements could open and close the active site in opposition to the actin-binding cleft, helping explain the opposing affinities of myosin for actin and nucleotide. To directly examine conformational changes across the active site during the ATPase cycle we have genetically engineered a mutant of chicken smooth-muscle myosin, F344W motor domain essential light chain, which contains a single tryptophan (344W) located on a short loop between two alpha helixes that traverse the upper-50 kD subdomain in front of the active site. Fluorescence resonance energy transfer was examined between the 344W donor probe and 2'(3')-O-(N-methylanthraniloyl) (mant)-nucleotide acceptor probes in the active site of this construct. The observed fluorescence resonance energy transfer efficiencies were 6.4% in the presence of mant ADP and 23.8% in the presence of mant ATP, corresponding to distances of 33.4 A and 24.9 A, respectively. Our results are consistent with structural rearrangements in which there is an 8.5-A closure between the 344W residue and the mant moiety during the transition from the strongly (ADP) to weakly (ATP) actin-bound states of the myosin ATPase cycle.
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Affiliation(s)
- C Ian Robertson
- Department of Molecular Physiology and Biophysics, University of Vermont, College of Medicine, Burlington, Vermont, USA
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27
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Sweeney HL, Houdusse A. The motor mechanism of myosin V: insights for muscle contraction. Philos Trans R Soc Lond B Biol Sci 2005; 359:1829-41. [PMID: 15647159 PMCID: PMC1693472 DOI: 10.1098/rstb.2004.1576] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
It is 50 years since the sliding of actin and myosin filaments was proposed as the basis of force generation and shortening in striated muscle. Although this is now generally accepted, the detailed molecular mechanism of how myosin uses adenosine triphosphate to generate force during its cyclic interaction with actin is only now being unravelled. New insights have come from the unconventional myosins, especially myosin V. Myosin V is kinetically tuned to allow movement on actin filaments as a single molecule, which has led to new kinetic, mechanical and structural data that have filled in missing pieces of the actomyosin-chemo-mechanical transduction puzzle.
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Affiliation(s)
- H Lee Sweeney
- Department of Physiology, University of Pennsylvania School of Medicine, A700 Richards Building, 3700 Hamilton Walk, Philadelphia, PA 19104-6085, USA.
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28
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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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Russell RB, Alber F, Aloy P, Davis FP, Korkin D, Pichaud M, Topf M, Sali A. A structural perspective on protein-protein interactions. Curr Opin Struct Biol 2004; 14:313-24. [PMID: 15193311 DOI: 10.1016/j.sbi.2004.04.006] [Citation(s) in RCA: 185] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Structures of macromolecular complexes are necessary for a mechanistic description of biochemical and cellular processes. They can be solved by experimental methods, such as X-ray crystallography, NMR spectroscopy and electron microscopy, as well as by computational protein structure prediction, docking and bioinformatics. Recent advances and applications of these methods emphasize the need for hybrid approaches that combine a variety of data to achieve better efficiency, accuracy, resolution and completeness.
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30
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Lehman W, Craig R, Kendrick-Jones J, Sutherland-Smith AJ. An open or closed case for the conformation of calponin homology domains on F-actin? J Muscle Res Cell Motil 2004; 25:351-8. [PMID: 15548864 DOI: 10.1007/s10974-004-0690-7] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Calponin homology domains link many different proteins to the surface of actin filaments. However, details of the structural interactions involved and the methods used to determine them are controversial. In the case of the actin-binding protein utrophin, for example, several models have been proposed for the binding of utrophin's calponin homology domains to actin. We review and evaluate these models and their supporting data.
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Affiliation(s)
- William Lehman
- Department of Physiology and Biophysics, Boston University School of Medicine, 715 Albany Street, Boston, MA 02118, USA.
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31
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Holmes KC, Angert I, Kull FJ, Jahn W, Schröder RR. Electron cryo-microscopy shows how strong binding of myosin to actin releases nucleotide. Nature 2003; 425:423-7. [PMID: 14508495 DOI: 10.1038/nature02005] [Citation(s) in RCA: 303] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2003] [Accepted: 08/21/2003] [Indexed: 11/08/2022]
Abstract
Muscle contraction involves the cyclic interaction of the myosin cross-bridges with the actin filament, which is coupled to steps in the hydrolysis of ATP. While bound to actin each cross-bridge undergoes a conformational change, often referred to as the "power stroke", which moves the actin filament past the myosin filaments; this is associated with the release of the products of ATP hydrolysis and a stronger binding of myosin to actin. The association of a new ATP molecule weakens the binding again, and the attached cross-bridge rapidly dissociates from actin. The nucleotide is then hydrolysed, the conformational change reverses, and the myosin cross-bridge reattaches to actin. X-ray crystallography has determined the structural basis of the power stroke, but it is still not clear why the binding of actin weakens that of the nucleotide and vice versa. Here we describe, by fitting atomic models of actin and the myosin cross-bridge into high-resolution electron cryo-microscopy three-dimensional reconstructions, the molecular basis of this linkage. The closing of the actin-binding cleft when actin binds is structurally coupled to the opening of the nucleotide-binding pocket.
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Affiliation(s)
- Kenneth C Holmes
- Department of Biophysics, Max Planck Institute for Medical Research, 69120 Heidelberg, Germany.
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32
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Reubold TF, Eschenburg S, Becker A, Kull FJ, Manstein DJ. A structural model for actin-induced nucleotide release in myosin. Nat Struct Mol Biol 2003; 10:826-30. [PMID: 14502270 DOI: 10.1038/nsb987] [Citation(s) in RCA: 140] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2003] [Accepted: 08/07/2003] [Indexed: 11/08/2022]
Abstract
Myosins are molecular motor proteins that harness the chemical energy stored in ATP to produce directed force along actin filaments. Complex communication pathways link the catalytic nucleotide-binding region, the structures responsible for force amplification and the actin-binding domain of myosin. We have crystallized the nucleotide-free motor domain of myosin II in a new conformation in which switch I and switch II, conserved loop structures involved in nucleotide binding, have moved away from the nucleotide-binding pocket. These movements are linked to rearrangements of the actin-binding region, which illuminate a previously unobserved communication pathway between the nucleotide-binding pocket and the actin-binding region, explain the reciprocal relationship between actin and nucleotide affinity and suggest a new mechanism for product release in myosin family motors.
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Affiliation(s)
- Thomas F Reubold
- Abteilung Biophysik, Max-Planck Institut für medizinische Forschung, Jahnstr. 29, D-69120 Heidelberg, Germany
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