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Cheng YS, Matusovskiy OS, Rassier DE. Cleavage of loops 1 and 2 in skeletal muscle heavy meromyosin (HMM) leads to a decreased function. Arch Biochem Biophys 2018; 661:168-177. [PMID: 30465737 DOI: 10.1016/j.abb.2018.11.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Revised: 10/31/2018] [Accepted: 11/04/2018] [Indexed: 11/26/2022]
Abstract
BACKGROUND The mechanical work and the actin-activated ATP kinetics in skeletal muscles are closely associated with two surface loops that are present in the myosin molecule: loop 1 and loop 2. They are located close to the ATP-loop (loop 1), and the actin binding domain (loop 2). In this study we investigated the roles of loops 1 and 2 in the regulation of the load-dependent velocity of actin sliding and ATPase activity. METHODS Heavy meromyosin (HMM) from rabbit skeletal muscle was subjected to limited tryptic proteolysis to obtain fragments containing different amounts of loops 1 and 2. The amino-acid sequences of these fragments were confirmed with quantitative mass-spectrometry. The velocity of actin motility propelled by the HMM fragments was measured using in-vitro motility assays, with varying loads induced by the addition of different concentrations of α-actinin. RESULTS The load-dependent velocity of the myosin-propelled actin motility, and the fraction of actin filaments motility, were decreased in close association with the depletion of loop 1 in the HMM. The ATPase activity was decreased in close association with depletion of loops 1 and 2. CONCLUSIONS Loop 1 is responsible for regulating the load-dependent velocity of actin motility. GENERAL SIGNIFICANCE Myosin-actin interaction is closely regulated by two flexible loops in the structure of myosin. The results of this study are important for the understanding of the molecular mechanisms of contraction, and therefore the most basic functions of life, such as locomotion, heart beating, and breathing.
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Affiliation(s)
- Yu-Shu Cheng
- Department of Kinesiology and Physical Education, McGill University, Montreal, Canada
| | - Oleg S Matusovskiy
- Department of Kinesiology and Physical Education, McGill University, Montreal, Canada
| | - Dilson E Rassier
- Department of Kinesiology and Physical Education, McGill University, Montreal, Canada.
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2
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The Conserved Lysine-265 Allosterically Modulates Nucleotide- and Actin-binding Site Coupling in Myosin-2. Sci Rep 2017; 7:7650. [PMID: 28794442 PMCID: PMC5550493 DOI: 10.1038/s41598-017-07933-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Accepted: 07/05/2017] [Indexed: 11/18/2022] Open
Abstract
Myosin motor proteins convert chemical energy into force and movement through their interactions with nucleotide and filamentous actin (F-actin). The evolutionarily conserved lysine-265 (K265) of the myosin-2 motor from Dictyostelium discoideum (Dd) is proposed to be a key residue in an allosteric communication pathway that mediates actin-nucleotide coupling. To better understand the role of K265, point mutations were introduced within the Dd myosin-2 M765-2R framework, replacing this lysine with alanine (K265A), glutamic acid (K265E) or glutamine (K265Q), and the functional and kinetic properties of the resulting myosin motors were assessed. The alanine and glutamic acid substitutions reduced actin-activated ATPase activity, slowed the in vitro sliding velocity and attenuated the inhibitory potential of the allosteric myosin inhibitor pentabromopseudilin (PBP). However, glutamine substitution did not substantially change these parameters. Structural modelling suggests that K265 interacts with D590 and Q633 to establish a pivotal allosteric branching point. Based on our results, we propose: (1) that the K265-D590 interaction functions to reduce myosins basal ATPase activity in the absence of F-actin, and (2) that the dynamic formation of the K265-Q633 salt bridge upon actin cleft closure regulates the activation of product release by actin filaments.
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3
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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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4
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Heissler SM, Liu X, Korn ED, Sellers JR. Kinetic characterization of the ATPase and actin-activated ATPase activities of Acanthamoeba castellanii myosin-2. J Biol Chem 2013; 288:26709-20. [PMID: 23897814 DOI: 10.1074/jbc.m113.485946] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phosphorylation of Ser-639 in loop-2 of the catalytic motor domain of the heavy chain of Acanthamoeba castellanii myosin-2 and the phosphomimetic mutation S639D have been shown previously to down-regulate the actin-activated ATPase activity of both the full-length myosin and single-headed subfragment-1 (Liu, X., Lee, D. Y., Cai, S., Yu, S., Shu, S., Levine, R. L., and Korn, E. D. (2013) Proc. Natl. Acad. Sci. U.S.A. 110, E23-E32). In the present study we determined the kinetic constants for each step in the myosin and actomyosin ATPase cycles of recombinant wild-type S1 and S1-S639D. The kinetic parameter predominantly affected by the S639D mutation is the actin-activated release of inorganic phosphate from the acto myosin·ADP·Pi complex, which is the rate-limiting step in the steady-state actomyosin ATPase cycle. As consequence of this change, the duty ratio of this conventional myosin decreases. We speculate on the effect of Ser-639 phosphorylation on the processive behavior of myosin-2 filaments.
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Affiliation(s)
- Sarah M Heissler
- From the Laboratory of Molecular Physiology and the Laboratory of Cell Biology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892-8015
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5
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Kalganov A, Shalabi N, Zitouni N, Kachmar LH, Lauzon AM, Rassier DE. Forces measured with micro-fabricated cantilevers during actomyosin interactions produced by filaments containing different myosin isoforms and loop 1 structures. Biochim Biophys Acta Gen Subj 2012; 1830:2710-2719. [PMID: 23220701 DOI: 10.1016/j.bbagen.2012.11.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2012] [Revised: 11/23/2012] [Accepted: 11/26/2012] [Indexed: 10/27/2022]
Abstract
BACKGROUND There is evidence that the actin-activated ATP kinetics and the mechanical work produced by muscle myosin molecules are regulated by two surface loops, located near the ATP binding pocket (loop 1), and in a region that interfaces with actin (loop 2). These loops regulate force and velocity of contraction, and have been investigated mostly in single molecules. There is a lack of information of the work produced by myosin molecules ordered in filaments and working cooperatively, which is the actual muscle environment. METHODS We use micro-fabricated cantilevers to measure forces produced by myosin filaments isolated from mollusk muscles, skeletal muscles, and smooth muscles containing variations in the structure of loop 1 (tonic and phasic myosins). We complemented the experiments with in-vitro assays to measure the velocity of actin motility. RESULTS Smooth muscle myosin filaments produced more force than skeletal and mollusk myosin filaments when normalized per filament overlap. Skeletal muscle myosin propelled actin filaments in a higher sliding velocity than smooth muscle myosin. The values for force and velocity were consistent with previous studies using myosin molecules, and suggest a close correlation with the myosin isoform and structure of surface loop 1. GENERAL SIGNIFICANCE The technique using micro-fabricated cantilevers to measure force of filaments allows for the investigation of the relation between myosin structure and contractility, allowing experiments to be conducted with an array of different myosin isoforms. Using the technique we observed that the work produced by myosin molecules is regulated by amino-acid sequences aligned in specific loops.
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Affiliation(s)
- Albert Kalganov
- Department of Kinesiology and Physical Education, Faculty of Education, McGill University, Canada
| | - Nabil Shalabi
- Department of Mechanical Engineering, Faculty of Engineering McGill University, Canada
| | - Nedjma Zitouni
- Meakins-Christie Laboratories, McGill University, Canada; Department of Experimental Medicine, Faculty of Medicine McGill University, Canada
| | - Linda Hussein Kachmar
- Meakins-Christie Laboratories, McGill University, Canada; Department of Experimental Medicine, Faculty of Medicine McGill University, Canada
| | - Anne-Marie Lauzon
- Meakins-Christie Laboratories, McGill University, Canada; Department of Experimental Medicine, Faculty of Medicine McGill University, Canada; Departments of Physics, Faculty of Science, McGill University, Canada; Department of Physiology, Faculty of Medicine, McGill University, Canada
| | - Dilson E Rassier
- Department of Kinesiology and Physical Education, Faculty of Education, McGill University, Canada; Meakins-Christie Laboratories, McGill University, Canada; Department of Experimental Medicine, Faculty of Medicine McGill University, Canada; Departments of Physics, Faculty of Science, McGill University, Canada; Department of Physiology, Faculty of Medicine, McGill University, Canada.
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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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Tominaga M, Nakano A. Plant-Specific Myosin XI, a Molecular Perspective. FRONTIERS IN PLANT SCIENCE 2012; 3:211. [PMID: 22973289 PMCID: PMC3437519 DOI: 10.3389/fpls.2012.00211] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2012] [Accepted: 08/21/2012] [Indexed: 05/04/2023]
Abstract
In eukaryotic cells, organelle movement, positioning, and communications are critical for maintaining cellular functions and are highly regulated by intracellular trafficking. Directional movement of motor proteins along the cytoskeleton is one of the key regulators of such trafficking. Most plants have developed a unique actin-myosin system for intracellular trafficking. Although the composition of myosin motors in angiosperms is limited to plant-specific myosin classes VIII and XI, there are large families of myosins, especially in class XI, suggesting functional diversification among class XI members. However, the molecular properties and regulation of each myosin XI member remains unclear. To achieve a better understanding of the plant-specific actin-myosin system, the characterization of myosin XI members at the molecular level is essential. In the first half of this review, we summarize the molecular properties of tobacco 175-kDa myosin XI, and in the later half, we focus on myosin XI members in Arabidopsis thaliana. Through detailed comparison of the functional domains of these myosins with the functional domain of myosin V, we look for possible diversification in enzymatic and mechanical properties among myosin XI members concomitant with their regulation.
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Affiliation(s)
- Motoki Tominaga
- Molecular Membrane Biology Laboratory, RIKEN Advanced Science InstituteWako, Saitama, Japan
- Japan Science and Technology Agency, PRESTOKawaguchi, Saitama, Japan
- *Correspondence: Motoki Tominaga, Molecular Membrane Biology Laboratory, RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan. e-mail:
| | - Akihiko Nakano
- Molecular Membrane Biology Laboratory, RIKEN Advanced Science InstituteWako, Saitama, Japan
- Department of Biological Sciences, Graduate School of Science, University of TokyoBunkyo-ku, Tokyo, Japan
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8
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Patel DM, Ahmad SF, Weiss DG, Gerke V, Kuznetsov SA. Annexin A1 is a new functional linker between actin filaments and phagosomes during phagocytosis. J Cell Sci 2011; 124:578-88. [PMID: 21245195 DOI: 10.1242/jcs.076208] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Remodelling of the actin cytoskeleton plays a key role in particle internalisation and the phagosome maturation processes. Actin-binding proteins (ABPs) are the main players in actin remodelling but the precise role of these proteins in phagocytosis needs to be clarified. Annexins, a group of ABPs, are known to be present on phagosomes. Here, we identified annexin A1 as a factor that binds to isolated latex bead phagosomes (LBPs) in the presence of Ca(2+) and facilitates the F-actin-LBP interaction in vitro. In macrophages the association of endogenous annexin A1 with LBP membranes was strongly correlated with the spatial and temporal accumulation of F-actin at the LBP. Annexin A1 was found on phagocytic cups and around early phagosomes, where the F-actin was prominently concentrated. After uptake was completed, annexin A1, along with F-actin, dissociated from the nascent LBP surface. At later stages of phagocytosis annexin A1 transiently concentrated only around those LBPs that showed transient F-actin accumulation ('actin flashing'). Downregulation of annexin A1 expression resulted in impaired phagocytosis and actin flashing. These data identify annexin A1 as an important component of phagocytosis that appears to link actin accumulation to different steps of phagosome formation.
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Affiliation(s)
- Devang M Patel
- Institute of Biological Sciences, Cell Biology and Biosystems Technology, University of Rostock, Albert-Einstein Straße 3, Rostock 18059, Germany
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9
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Tehver R, Thirumalai D. Rigor to post-rigor transition in myosin V: link between the dynamics and the supporting architecture. Structure 2010; 18:471-81. [PMID: 20399184 DOI: 10.1016/j.str.2010.01.019] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2009] [Revised: 01/01/2010] [Accepted: 01/05/2010] [Indexed: 10/19/2022]
Abstract
The detachment kinetics from actin upon ATP binding is a key step in the reaction cycle of myosin V. We show that a network of residues, constituting the allostery wiring diagram (AWD), that trigger the rigor (R) to post-rigor (PR) transition, span key structural elements from the ATP and actin-binding regions. Several of the residues are in the 33 residue helix (H18), P loop, and switch I. Brownian dynamics simulations show that a hierarchy of kinetically controlled local structural changes leads to the opening of the "cleft" region, resulting in the detachment of the motor domain from actin. Movements in switch I and P loop facilitate changes in the rest of the motor domain, in particular the rotation of H18, whose stiffness within the motor domain is crucial in the R --> PR transition. The finding that residues in the AWD also drive the kinetics of the R --> PR transition shows how the myosin architecture regulates the allosteric movements during the reaction cycle.
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Affiliation(s)
- Riina Tehver
- Biophysics Program, Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742, USA
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10
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Whiteley NM, Magnay JL, McCleary SJ, Nia SK, El Haj AJ, Rock J. Characterisation of myosin heavy chain gene variants in the fast and slow muscle fibres of gammarid amphipods. Comp Biochem Physiol A Mol Integr Physiol 2010; 157:116-22. [PMID: 20570748 DOI: 10.1016/j.cbpa.2010.05.014] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2010] [Revised: 05/23/2010] [Accepted: 05/24/2010] [Indexed: 10/19/2022]
Abstract
Recent molecular work has revealed a large diversity of myosin heavy chain (MyHC) gene variants in the abdominal musculature of gammarid amphipods. An unusual truncated MyHC transcript from the loop 1 region (Variant A(3)) was consistently observed in multiple species and populations. The current study aimed to determine whether this MyHC variant is specific to a particular muscle fibre type, as a change in net charge to the loop 1 region of Variant A(3) could be functionally significant. The localisation of different fibre types within the abdominal musculature of several gammarid species revealed that the deep flexor and extensor muscles are fast-twitch muscle fibres. The dorsal superficial muscles were identified as slow fibres and the muscles extrinsic to the pleopods were identified as intermediate fibres. Amplification of loop 1 region mRNA from isolated superficial extensor and deep flexor muscles, and subsequent liquid chromatography and sequence analysis revealed that Variant A(3) was the primary MyHC variant in slow muscles, and the conserved A(1) sequence was the primary variant in fast muscles. The specific role of Variant A(3) in the slow muscles remains to be investigated.
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11
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Burghardt TP, Neff KL, Wieben ED, Ajtai K. Myosin individualized: single nucleotide polymorphisms in energy transduction. BMC Genomics 2010; 11:172. [PMID: 20226094 PMCID: PMC2848645 DOI: 10.1186/1471-2164-11-172] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2009] [Accepted: 03/15/2010] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND Myosin performs ATP free energy transduction into mechanical work in the motor domain of the myosin heavy chain (MHC). Energy transduction is the definitive systemic feature of the myosin motor performed by coordinating in a time ordered sequence: ATP hydrolysis at the active site, actin affinity modulation at the actin binding site, and the lever-arm rotation of the power stroke. These functions are carried out by several conserved sub-domains within the motor domain. Single nucleotide polymorphisms (SNPs) affect the MHC sequence of many isoforms expressed in striated muscle, smooth muscle, and non-muscle tissue. The purpose of this work is to provide a rationale for using SNPs as a functional genomics tool to investigate structurefunction relationships in myosin. In particular, to discover SNP distribution over the conserved sub-domains and surmise what it implies about sub-domain stability and criticality in the energy transduction mechanism. RESULTS An automated routine identifying human nonsynonymous SNP amino acid missense substitutions for any MHC gene mined the NCBI SNP data base. The routine tested 22 MHC genes coding muscle and non-muscle isoforms and identified 89 missense mutation positions in the motor domain with 10 already implicated in heart disease and another 8 lacking sequence homology with a skeletal MHC isoform for which a crystallographic model is available. The remaining 71 SNP substitutions were found to be distributed over MHC with 22 falling outside identified functional sub-domains and 49 in or very near to myosin sub-domains assigned specific crucial functions in energy transduction. The latter includes the active site, the actin binding site, the rigid lever-arm, and regions facilitating their communication. Most MHC isoforms contained SNPs somewhere in the motor domain. CONCLUSIONS Several functional-crucial sub-domains are infiltrated by a large number of SNP substitution sites suggesting these domains are engineered by evolution to be too-robust to be disturbed by otherwise intrusive sequence changes. Two functional sub-domains are SNP-free or relatively SNP-deficient but contain many disease implicated mutants. These sub-domains are apparently highly sensitive to any missense substitution suggesting they have failed to evolve a robust sequence paradigm for performing their function.
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Affiliation(s)
- Thomas P Burghardt
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, 200 First Street SW, Rochester, MN 55905, USA
- Department of Physiology and Biomedical Engineering, Mayo Clinic Rochester, 200 First Street SW, Rochester, MN 55905, USA
| | - Kevin L Neff
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, 200 First Street SW, Rochester, MN 55905, USA
| | - Eric D Wieben
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, 200 First Street SW, Rochester, MN 55905, USA
| | - Katalin Ajtai
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, 200 First Street SW, Rochester, MN 55905, USA
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12
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Unique charge distribution in surface loops confers high velocity on the fast motor protein Chara myosin. Proc Natl Acad Sci U S A 2009; 106:21585-90. [PMID: 19955408 DOI: 10.1073/pnas.0910787106] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Most myosins have a positively charged loop 2 with a cluster of lysine residues that bind to the negatively charged N-terminal segment of actin. However, the net charge of loop 2 of very fast Chara myosin is zero and there is no lysine cluster in it. In contrast, Chara myosin has a highly positively charged loop 3. To elucidate the role of these unique surface loops of Chara myosin in its high velocity and high actin-activated ATPase activity, we have undertaken mutational analysis using recombinant Chara myosin motor domain. It was found that net positive charge in loop 3 affected V(max) and K(app) of actin activated ATPase activity, while it affected the velocity only slightly. The net positive charge in loop 2 affected K(app) and the velocity, although it did not affect V(max). Our results suggested that Chara myosin has evolved to have highly positively charged loop 3 for its high ATPase activity and have less positively charged loop 2 for its high velocity. Since high positive charge in loop 3 and low positive charge in loop 2 seem to be one of the reasons for Chara myosin's high velocity, we manipulated charge contents in loops 2 and 3 of Dictyostelium myosin (class II). Removing positive charge from loop 2 and adding positive charge to loop 3 of Dictyostelium myosin made its velocity higher than that of the wild type, suggesting that the charge strategy in loops 2 and 3 is widely applicable.
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13
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Linking functional molecular variation with environmental gradients: Myosin gene diversity in a crustacean broadly distributed across variable thermal environments. Gene 2009; 437:60-70. [DOI: 10.1016/j.gene.2009.02.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2008] [Revised: 01/09/2009] [Accepted: 02/07/2009] [Indexed: 11/19/2022]
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14
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Kambara T, Ikebe M. A unique ATP hydrolysis mechanism of single-headed processive myosin, myosin IX. J Biol Chem 2005; 281:4949-57. [PMID: 16338935 DOI: 10.1074/jbc.m509141200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Recent studies have revealed that myosin IX is a single-headed processive myosin, yet it is unclear how myosin IX can achieve the processive movement. Here we studied the mechanism of ATP hydrolysis cycle of actomyosin IXb. We found that myosin IXb has a rate-limiting ATP hydrolysis step unlike other known myosins, thus populating the prehydrolysis intermediate (M.ATP). M.ATP has a high affinity for actin, and, unlike other myosins, the dissociation of M.ATP from actin was extremely slow, thus preventing myosin from dissociating away from actin. The ADP dissociation step was 10-fold faster than the overall ATP hydrolysis cycle rate and thus not rate-limiting. We propose the following model for single-headed processive myosin. Upon the formation of the M.ATP intermediate, the tight binding of actomyosin IX at the interface is weakened. However, the head is kept in close proximity to actin due to the tethering role of loop 2/large unique insertion of myosin IX. There is enough freedom for the myosin head to find the next location of the binding site along with the actin filament before complete dissociation from the filament. After ATP hydrolysis, Pi is quickly released to form a strong actin binding form, and a power stroke takes place.
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Affiliation(s)
- Taketoshi Kambara
- Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA
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15
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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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16
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Tóth J, Kovács M, Wang F, Nyitray L, Sellers JR. Myosin V from Drosophila reveals diversity of motor mechanisms within the myosin V family. J Biol Chem 2005; 280:30594-603. [PMID: 15980429 DOI: 10.1074/jbc.m505209200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Myosin V is the best characterized vesicle transporter in vertebrates, but it has been unknown as to whether all members of the myosin V family share a common, evolutionarily conserved mechanism of action. Here we show that myosin V from Drosophila has a strikingly different motor mechanism from that of vertebrate myosin Va, and it is a nonprocessive, ensemble motor. Our steady-state and transient kinetic measurements on single-headed constructs reveal that a single Drosophila myosin V molecule spends most of its mechanochemical cycle time detached from actin, therefore it has to function in processive units that comprise several molecules. Accordingly, in in vitro motility assays, double-headed Drosophila myosin V requires high surface concentrations to exhibit a continuous translocation of actin filaments. Our comparison between vertebrate and fly myosin V demonstrates that the well preserved function of myosin V motors in cytoplasmic transport can be accomplished by markedly different underlying mechanisms.
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Affiliation(s)
- Judit Tóth
- Laboratory of Molecular Physiology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892-1762, USA
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Patchell VB, Gallon CE, Evans JS, Gao Y, Perry SV, Levine BA. The regulatory effects of tropomyosin and troponin-I on the interaction of myosin loop regions with F-actin. J Biol Chem 2005; 280:14469-75. [PMID: 15695827 DOI: 10.1074/jbc.m414202200] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The N terminus of skeletal myosin light chain 1 and the cardiomyopathy loop of human cardiac myosin have been shown previously to bind to actin in the presence and absence of tropomyosin (Patchell, V. B., Gallon, C. E., Hodgkin, M. A., Fattoum, A., Perry, S. V., and Levine, B. A. (2002) Eur. J. Biochem. 269, 5088-5100). We have extended this work and have shown that segments corresponding to other regions of human cardiac beta-myosin, presumed to be sites of interaction with F-actin (residues 554-584, 622-646, and 633-660), likewise bind independently to actin under similar conditions. The binding to F-actin of a peptide spanning the minimal inhibitory segment of human cardiac troponin I (residues 134-147) resulted in the dissociation from F-actin of all the myosin peptides bound to it either individually or in combination. Troponin C neutralized the effect of the inhibitory peptide on the binding of the myosin peptides to F-actin. We conclude that the binding of the inhibitory region of troponin I to actin, which occurs during relaxation in muscle when the calcium concentration is low, imposes conformational changes that are propagated to different locations on the surface of actin. We suggest that the role of tropomyosin is to facilitate the transmission of structural changes along the F-actin filament so that the monomers within a structural unit are able to interact with myosin.
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Affiliation(s)
- Valerie B Patchell
- Division of Medical Sciences, School of Medicine, University of Birmingham, Birmingham B15 2TT, United Kingdom
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18
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Ajtai K, Garamszegi SP, Watanabe S, Ikebe M, Burghardt TP. The myosin cardiac loop participates functionally in the actomyosin interaction. J Biol Chem 2004; 279:23415-21. [PMID: 15020589 DOI: 10.1074/jbc.m310775200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The motor protein myosin in association with actin transduces chemical free energy in ATP into work in the form of actin translation against an opposing force. Mediating the actomyosin interaction in myosin is an actin binding site distributed among several peptides on the myosin surface including surface loops contributing to affinity and actin regulation of myosin ATPase. A structured surface loop on beta-cardiac myosin, the cardiac or C-loop, was recently demonstrated to affect myosin ATPase and was indirectly implicated in the actomyosin interaction. The C-loop is a conserved feature of all myosin isoforms with crystal structures, suggesting that it is an essential part of the core energy transduction machinery. It is shown here that proteolytic digestion of the C-loop in beta-cardiac myosin eliminates actin-activated myosin ATPase and reduces actomyosin affinity in rigor more than 100-fold. Studies of C-loop function in smooth muscle myosin were also undertaken using site-directed mutagenesis. Mutagenesis of a single charged residue in the C-loop of smooth muscle myosin alters actomyosin affinity and doubles myosin in vitro motility and actin-activated ATPase velocities, thereby involving a charged region of the loop in the actomyosin interaction. It appears likely that the C-loop is an essential electrostatic binding site for actin involved in modulation of actomyosin affinity and regulation of actomyosin ATPase velocity.
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Affiliation(s)
- Katalin Ajtai
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, Minnesota 55905, USA
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19
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Tsiavaliaris G, Fujita-Becker S, Manstein DJ. Molecular engineering of a backwards-moving myosin motor. Nature 2004; 427:558-61. [PMID: 14765199 DOI: 10.1038/nature02303] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2003] [Accepted: 12/19/2003] [Indexed: 11/09/2022]
Abstract
All members of the diverse myosin superfamily have a highly conserved globular motor domain that contains the actin- and nucleotide-binding sites and produces force and movement. The light-chain-binding domain connects the motor domain to a variety of functionally specialized tail domains and amplifies small structural changes in the motor domain through rotation of a lever arm. Myosins move on polarized actin filaments either forwards to the barbed (+) or backwards to the pointed (-) end. Here, we describe the engineering of an artificial backwards-moving myosin from three pre-existing molecular building blocks. These blocks are: a forward-moving class I myosin motor domain, a directional inverter formed by a four-helix bundle segment of human guanylate-binding protein-1 and an artificial lever arm formed by two alpha-actinin repeats. Our results prove that reverse-direction movement of myosins can be achieved simply by rotating the direction of the lever arm 180 degrees.
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Affiliation(s)
- Georgios Tsiavaliaris
- Institut für Biophysikalische Chemie, Medizinische Hochschule Hannover, OE 4350, Carl-Neuberg-Strasse 1, D-30623 Hannover, Germany
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20
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Sasaki N, Ohkura R, Sutoh K. Dictyostelium myosin II as a model to study the actin-myosin interactions during force generation. J Muscle Res Cell Motil 2003; 23:697-702. [PMID: 12952068 DOI: 10.1023/a:1024415409406] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
During steady-state ATP hydrolysis by actomyosin, myosin cyclically passes through strong actin-binding states and weak actin-binding states, depending on the nature of a nucleotide in the ATPase site. This cyclic change of actin-myosin affinity is coupled with the lever-arm swing and is critical for the sliding motion and force generation of actomyosin. To understand the structure-function relationship of this ATPase-dependent actin-myosin interaction, Dictyostelium myosin II has been extensively used for site-directed mutagenesis. By generating a large number of mutant myosins, two hydrophobic actin-binding sites have been revealed, located at the tip of the upper and lower 50 K subdomains of Dictyostelium myosin, one of which is the 'cardiomyopathy loop'. Furthermore, the slight change in relative orientation of these two hydrophobic sites around the 'strut loop' has been shown to work as a switch to turn on and off the strong binding to actin. Once the switch is turned off, myosin enters in the weak-binding state, where ionic interactions between actin and the 'loop 2' of myosin become the dominant force to maintain the actin-myosin association. The details of actin-myosin interactions revealed by the Dictyostelium system can serve as a framework for further examinations of the myosin superfamily proteins.
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Affiliation(s)
- Naoya Sasaki
- Center for Interdisciplinary Research, Tohoku University, Aramaki-aza-aoba, Aoba-ku, Sendai, Miyagi 980-8579, Japan
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21
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Holmes JM, Whiteley NM, Magnay JL, El Haj AJ. Comparison of the variable loop regions of myosin heavy chain genes from Antarctic and temperate isopods. Comp Biochem Physiol B Biochem Mol Biol 2002; 131:349-59. [PMID: 11959017 DOI: 10.1016/s1096-4959(01)00509-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The evolutionary adaptations of functional genes to life at low temperatures are not well characterised in marine and fresh water invertebrates. Temperature has been shown to affect the functional characteristics of fish muscles, with changes in the velocity of shortening and ATPase activity being associated with myosin heavy chain (MyHC) isoform composition and the structure of the surface loop regions. Two PCR products spanning loops 1 and 2 of a MyHC gene from an Antarctic isopod (Glyptonotus antarcticus) were sequenced and compared with those of a temperate isopod (Idotea resecata), slow and fast fibres from lobster (Homarus gammarus) and a cold water amphipod (Eulimnogammarus verrucosus), revealing specific differences between the species, possibly related to fibre type and habitat temperature. The loop 2 region from G. antarcticus myosin was cloned and used for Northern analysis of total RNA from the other species. The cloned myosin cDNA hybridised specifically to a 6.6-kb transcript, in G. antarcticus muscle. In contrast, cDNA probes for lobster slow myosin and actin hybridised to muscle RNA from all species, demonstrating that a distinct MyHC isoform is expressed in the Antarctic isopod, as opposed to the temperate species. The inter- and intra-specific sequence differences in loop 2 region suggest that this may be a site for muscle adaptation to enable function at the low temperatures found in the Southern Ocean.
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Affiliation(s)
- J M Holmes
- Centre for Science and Technology, School of Postgraduate Medicine, Keele University, Thornburrow Drive, North Staffordshire ST4 7QB, Stoke on Trent, UK.
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22
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Abstract
This review focuses on selected papers that illustrate an historical perspective and the current knowledge of myosin structure and function in protists. The review contains a general description of myosin structure, a phylogenetic tree of the myosin classes, and descriptions of myosin isoforms identified in protists. Each myosin is discussed within the context of the taxonomic group of the organism in which the myosin has been identified. Domain structure, cellular location, function, and regulation are described for each myosin.
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Affiliation(s)
- R H Gavin
- Department of Biology, Brooklyn College, City University of New York, New York 11210, USA
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23
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Straube A, Enard W, Berner A, Wedlich-Söldner R, Kahmann R, Steinberg G. A split motor domain in a cytoplasmic dynein. EMBO J 2001; 20:5091-100. [PMID: 11566874 PMCID: PMC125636 DOI: 10.1093/emboj/20.18.5091] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The heavy chain of dynein forms a globular motor domain that tightly couples the ATP-cleavage region and the microtubule-binding site to transform chemical energy into motion along the cytoskeleton. Here we show that, in the fungus Ustilago maydis, two genes, dyn1 and dyn2, encode the dynein heavy chain. The putative ATPase region is provided by dyn1, while dyn2 includes the predicted microtubule-binding site. Both genes are located on different chromosomes, are transcribed into independent mRNAs and are translated into separate polypeptides. Both Dyn1 and Dyn2 co-immunoprecipitated and co-localized within growing cells, and Dyn1-Dyn2 fusion proteins partially rescued mutant phenotypes, suggesting that both polypeptides interact to form a complex. In cell extracts the Dyn1-Dyn2 complex dissociated, and microtubule affinity purification indicated that Dyn1 or associated polypeptides bind microtubules independently of Dyn2. Both Dyn1 and Dyn2 were essential for cell survival, and conditional mutants revealed a common role in nuclear migration, cell morphogenesis and microtubule organization, indicating that the Dyn1-Dyn2 complex serves multiple cellular functions.
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Affiliation(s)
- Anne Straube
- Institut für Genetik und Mikrobiologie, LMU, Maria-Ward-Straße 1a, D-80638 München, Germany
Present address: Max-Planck-Institut für terrestrische Mikrobiologie, Karl-von-Frisch-Straße, D-35043 Marburg, Germany Present address: Max-Planck-Institut für evolutionäre Anthropologie, Inselstraße 22, D-04103 Leipzig, Germany Present address: Vision in Business Ltd, 30 City Road, London EC1Y 2AY, UK Corresponding author e-mail:
| | - Wolfgang Enard
- Institut für Genetik und Mikrobiologie, LMU, Maria-Ward-Straße 1a, D-80638 München, Germany
Present address: Max-Planck-Institut für terrestrische Mikrobiologie, Karl-von-Frisch-Straße, D-35043 Marburg, Germany Present address: Max-Planck-Institut für evolutionäre Anthropologie, Inselstraße 22, D-04103 Leipzig, Germany Present address: Vision in Business Ltd, 30 City Road, London EC1Y 2AY, UK Corresponding author e-mail:
| | - Alexandra Berner
- Institut für Genetik und Mikrobiologie, LMU, Maria-Ward-Straße 1a, D-80638 München, Germany
Present address: Max-Planck-Institut für terrestrische Mikrobiologie, Karl-von-Frisch-Straße, D-35043 Marburg, Germany Present address: Max-Planck-Institut für evolutionäre Anthropologie, Inselstraße 22, D-04103 Leipzig, Germany Present address: Vision in Business Ltd, 30 City Road, London EC1Y 2AY, UK Corresponding author e-mail:
| | - Roland Wedlich-Söldner
- Institut für Genetik und Mikrobiologie, LMU, Maria-Ward-Straße 1a, D-80638 München, Germany
Present address: Max-Planck-Institut für terrestrische Mikrobiologie, Karl-von-Frisch-Straße, D-35043 Marburg, Germany Present address: Max-Planck-Institut für evolutionäre Anthropologie, Inselstraße 22, D-04103 Leipzig, Germany Present address: Vision in Business Ltd, 30 City Road, London EC1Y 2AY, UK Corresponding author e-mail:
| | - Regine Kahmann
- Institut für Genetik und Mikrobiologie, LMU, Maria-Ward-Straße 1a, D-80638 München, Germany
Present address: Max-Planck-Institut für terrestrische Mikrobiologie, Karl-von-Frisch-Straße, D-35043 Marburg, Germany Present address: Max-Planck-Institut für evolutionäre Anthropologie, Inselstraße 22, D-04103 Leipzig, Germany Present address: Vision in Business Ltd, 30 City Road, London EC1Y 2AY, UK Corresponding author e-mail:
| | - Gero Steinberg
- Institut für Genetik und Mikrobiologie, LMU, Maria-Ward-Straße 1a, D-80638 München, Germany
Present address: Max-Planck-Institut für terrestrische Mikrobiologie, Karl-von-Frisch-Straße, D-35043 Marburg, Germany Present address: Max-Planck-Institut für evolutionäre Anthropologie, Inselstraße 22, D-04103 Leipzig, Germany Present address: Vision in Business Ltd, 30 City Road, London EC1Y 2AY, UK Corresponding author e-mail:
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24
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Abstract
High-resolution structures of the motor domain of myosin II and lower resolution actin-myosin structures have led to the "swinging lever arm" model for myosin force generation. The available kinetic data are not all easily reconciled with this model and understanding the final details of the myosin motor mechanism must await actin-myosin co-crystals. The observation that myosin can populate multiple states in the absence of actin has nonetheless led to significant insights. The currently known myosin structures correspond to defined kinetic states that bind weakly (K(d)>microM) to actin. It is possible that the myosin lever arm could complete its swing before strong binding to actin and force generation--a process that would correspond, in the absence of load, to a Brownian ratchet. We further suggest that, under load, internal springs within the myosin head could decouple force generation and lever arm movement.
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Affiliation(s)
- A Houdusse
- Structural Motility, Institut Curie CNRS, UMR 144, 26 rue d'Ulm, 75248 05 Paris Cedex, France.
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25
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Joel PB, Trybus KM, Sweeney HL. Two conserved lysines at the 50/20-kDa junction of myosin are necessary for triggering actin activation. J Biol Chem 2001; 276:2998-3003. [PMID: 11042210 DOI: 10.1074/jbc.m006930200] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Actin stimulates myosin's activity by inducing structural alterations that correlate with the transition from a weakly to a strongly bound state, during which time inorganic phosphate (P(i)) is released from myosin's active site. The surface loop at the 50/20-kDa junction of myosin (loop 2) is part of the actin interface. Here we demonstrate that elimination of two highly conserved lysines at the C-terminal end of loop 2 specifically blocks the ability of heavy meromyosin to undergo a weak to strong binding transition with actin in the presence of ATP. Removal of these lysines has no effect on strong binding in the absence of nucleotide, on the rate of ADP binding or release, or on the basal ATPase activity. We further show that the 16 amino acids of loop 2 preceding the lysine-rich region are not essential for actin activation, although they do modulate myosin's affinity for actin in the presence of ATP. We conclude that interaction of the conserved lysines with acidic residues in subdomain 1 of actin either triggers a structural change or stabilizes a conformation that is necessary for actin-activated release of P(i) and completion of the ATPase cycle.
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Affiliation(s)
- P B Joel
- Department of Molecular Physiology and Biophysics, University of Vermont College of Medicine, Burlington, Vermont 05405-0068, USA
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26
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Takahashi M, Takahashi K, Hiratsuka Y, Uchida K, Yamagishi A, Uyeda TQ, Yazawa M. Functional characterization of vertebrate nonmuscle myosin IIB isoforms using Dictyostelium chimeric myosin II. J Biol Chem 2001; 276:1034-40. [PMID: 11042201 DOI: 10.1074/jbc.m005370200] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The alternatively spliced isoform of nonmuscle myosin II heavy chain B (MHC-IIB) with an insert of 21 amino acids in the actin-binding surface loop (loop 2), MHC-IIB(B2), is expressed specifically in the central nervous system of vertebrates. To examine the role of the B2 insert in the motor activity of the myosin II molecule, we expressed chimeric myosin heavy chain molecules using the Dictyostelium myosin II heavy chain as the backbone. We replaced the Dictyostelium native loop 2 with either the noninserted form of loop 2 from human MHC-IIB or the B2-inserted form of loop 2 from human MHC-IIB(B2). The transformant Dictyostelium cells expressing only the B2-inserted chimeric myosin formed unusual fruiting bodies. We then assessed the function of chimeric proteins, using an in vitro motility assay and by measuring ATPase activities and binding to F-actin. We demonstrate that the insertion of the B2 sequence reduces the motor activity of Dictyostelium myosin II, with reduction of the maximal actin-activated ATPase activity and a decrease in the affinity for actin. In addition, we demonstrate that the native loop 2 sequence of Dictyostelium myosin II is required for the regulation of the actin-activated ATPase activity by phosphorylation of the regulatory light chain.
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Affiliation(s)
- M Takahashi
- Division of Biological Sciences and Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan.
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27
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Murphy CT, Spudich JA. Variable surface loops and myosin activity: accessories to a motor. J Muscle Res Cell Motil 2000; 21:139-51. [PMID: 10961838 DOI: 10.1023/a:1005610007209] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The catalytic head of myosin is a globular structure that has historically been divided into three segments of 25, 50, and 20 kDa. The solvent-exposed, proteolytically-sensitive surface loops of myosin that join these three segments are highly variable in their sequences. While surface loops have not traditionally been thought to affect enzymatic activities, these loops lie near the ATP and actin-binding sites and have been implicated in the modulation of myosin's kinetic activities. In this work we review the wealth of data regarding the loops that has accumulated over the years and discuss the roles of the loops in contributing to the different activities displayed by different myosin isoforms.
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Affiliation(s)
- C T Murphy
- Department of Biochemistry, Stanford University School of Medicine, CA 94305, USA
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28
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Abstract
The crystal structures of smooth muscle and scallop striated muscle myosin have both been completed in the past 18 months. Structural studies of unconventional myosins, in particular the stunning discovery that myosin VI moves backwards on actin, are starting to have deep impact on the field and have induced new ways of thinking about actin-based motility. Sophisticated genetic, biochemical and biophysical studies were used to test and refine hypotheses of the molecular mechanism of motility that were developed in the past. Although all these studies confirmed some aspects of these hypotheses, they also raised many new unresolved questions. Much of the evidence points to the importance of the actin-myosin binding process and an associated disorder-to-order transition.
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Affiliation(s)
- N Volkmann
- The Burnham Institute, La Jolla, 92037, USA.
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