1
|
Gargey A, Nesmelov YE. Electrostatic interaction of loop 1 and backbone of human cardiac myosin regulates the rate of ATP induced actomyosin dissociation. J Muscle Res Cell Motil 2022; 43:1-8. [PMID: 34825297 PMCID: PMC8897261 DOI: 10.1007/s10974-021-09611-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2021] [Accepted: 11/15/2021] [Indexed: 11/27/2022]
Abstract
Double mutation D208Q:K450L was introduced in the beta isoform of human cardiac myosin to remove the salt bridge D208:K450 connecting loop 1 and the seven-stranded beta sheet within the myosin head. Beta isoform-specific salt bridge D208:K450, restricting the flexibility of loop 1, was previously discovered in molecular dynamics simulations. Earlier it was proposed that loop 1 modulates nucleotide affinity to actomyosin and we hypothesized that the electrostatic interactions between loop 1 and myosin head backbone regulate ATP binding to and ADP dissociation from actomyosin, and therefore, the time of the strong actomyosin binding. To examine the hypothesis we expressed the wild type and mutant of the myosin head construct (1-843 amino acid residues) in differentiated C2C12 cells, and the kinetics of ATP-induced actomyosin dissociation and ADP release were characterized using stopped-flow spectrofluorometry. Both constructs exhibit a fast rate of ATP binding to actomyosin and a slow rate of ADP dissociation, showing that ADP release limits the time of the strongly bound state of actomyosin. We observed a faster rate of ATP-induced actomyosin dissociation with the mutant, compared to the wild type actomyosin. The rate of ADP release from actomyosin remains the same for the mutant and the wild type actomyosin. We conclude that the flexibility of loop 1 is a factor affecting the rate of ATP binding to actomyosin and actomyosin dissociation. The flexibility of loop 1 does not affect the rate of ADP release from human cardiac actomyosin.
Collapse
Affiliation(s)
- Akhil Gargey
- Department of Physics and Optical Science, University of North Carolina Charlotte, 9201 University City Blvd, Charlotte, NC, 28223, USA
- Department of Biological Science, University of North Carolina Charlotte, Charlotte, NC, 28223, USA
| | - Yuri E Nesmelov
- Department of Physics and Optical Science, University of North Carolina Charlotte, 9201 University City Blvd, Charlotte, NC, 28223, USA.
| |
Collapse
|
2
|
Gunther LK, Rohde JA, Tang W, Cirilo JA, Marang CP, Scott BD, Thomas DD, Debold EP, Yengo CM. FRET and optical trapping reveal mechanisms of actin activation of the power stroke and phosphate release in myosin V. J Biol Chem 2021; 295:17383-17397. [PMID: 33453985 DOI: 10.1074/jbc.ra120.015632] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2020] [Revised: 10/06/2020] [Indexed: 11/06/2022] Open
Abstract
Myosins generate force and motion by precisely coordinating their mechanical and chemical cycles, but the nature and timing of this coordination remains controversial. We utilized a FRET approach to examine the kinetics of structural changes in the force-generating lever arm in myosin V. We directly compared the FRET results with single-molecule mechanical events examined by optical trapping. We introduced a mutation (S217A) in the conserved switch I region of the active site to examine how myosin couples structural changes in the actin- and nucleotide-binding regions with force generation. Specifically, S217A enhanced the maximum rate of lever arm priming (recovery stroke) while slowing ATP hydrolysis, demonstrating that it uncouples these two steps. We determined that the mutation dramatically slows both actin-induced rotation of the lever arm (power stroke) and phosphate release (≥10-fold), whereas our simulations suggest that the maximum rate of both steps is unchanged by the mutation. Time-resolved FRET revealed that the structure of the pre- and post-power stroke conformations and mole fractions of these conformations were not altered by the mutation. Optical trapping results demonstrated that S217A does not dramatically alter unitary displacements or slow the working stroke rate constant, consistent with the mutation disrupting an actin-induced conformational change prior to the power stroke. We propose that communication between the actin- and nucleotide-binding regions of myosin assures a proper actin-binding interface and active site have formed before producing a power stroke. Variability in this coupling is likely crucial for mediating motor-based functions such as muscle contraction and intracellular transport.
Collapse
Affiliation(s)
- Laura K Gunther
- Department of Cellular and Molecular Physiology, Pennsylvania State College of Medicine, Hershey, Pennsylvania, USA
| | - John A Rohde
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota Twin Cities, Minneapolis, Minnesota, USA
| | - Wanjian Tang
- Department of Cellular and Molecular Physiology, Pennsylvania State College of Medicine, Hershey, Pennsylvania, USA
| | - Joseph A Cirilo
- Department of Cellular and Molecular Physiology, Pennsylvania State College of Medicine, Hershey, Pennsylvania, USA
| | - Christopher P Marang
- Department of Kinesiology, University of Massachusetts, Amherst, Massachusetts, USA
| | - Brent D Scott
- Department of Kinesiology, University of Massachusetts, Amherst, Massachusetts, USA
| | - David D Thomas
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota Twin Cities, Minneapolis, Minnesota, USA
| | - Edward P Debold
- Department of Kinesiology, University of Massachusetts, Amherst, Massachusetts, USA
| | - Christopher M Yengo
- Department of Cellular and Molecular Physiology, Pennsylvania State College of Medicine, Hershey, Pennsylvania, USA.
| |
Collapse
|
3
|
Glasheen BM, Ramanath S, Patel M, Sheppard D, Puthawala JT, Riley LA, Swank DM. Five Alternative Myosin Converter Domains Influence Muscle Power, Stretch Activation, and Kinetics. Biophys J 2019. [PMID: 29539400 DOI: 10.1016/j.bpj.2017.12.045] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Muscles have evolved to power a wide variety of movements. A protein component critical to varying power generation is the myosin isoform present in the muscle. However, how functional variation in muscle arises from myosin structure is not well understood. We studied the influence of the converter, a myosin structural region at the junction of the lever arm and catalytic domain, using Drosophila because its single myosin heavy chain gene expresses five alternative converter versions (11a-e). We created five transgenic fly lines, each forced to express one of the converter versions in their indirect flight muscle (IFM) fibers. Electron microscopy showed that the converter exchanges did not alter muscle ultrastructure. The four lines expressing converter versions (11b-e) other than the native IFM 11a converter displayed decreased flight ability. IFM fibers expressing converters normally found in the adult stage muscles generated up to 2.8-fold more power and displayed up to 2.2-fold faster muscle kinetics than fibers with converters found in the embryonic and larval stage muscles. Small changes to stretch-activated force generation only played a minor role in altering power output of IFM. Muscle apparent rate constants, derived from sinusoidal analysis of the chimeric converter fibers, showed a strong positive correlation between optimal muscle oscillation frequency and myosin attachment kinetics to actin, and an inverse correlation with detachment related cross-bridge kinetics. This suggests the myosin converter alters at least two rate constants of the cross-bridge cycle with changes to attachment and power stroke related kinetics having the most influence on setting muscle oscillatory power kinetics.
Collapse
Affiliation(s)
| | - Seemanti Ramanath
- Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, New York
| | - Monica Patel
- Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, New York
| | - Debra Sheppard
- Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, New York
| | - Joy T Puthawala
- Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, New York
| | - Lauren A Riley
- Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, New York
| | - Douglas M Swank
- Department of Biological Sciences, Rensselaer Polytechnic Institute, Troy, New York; Department of Biomedical Engineering and Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York.
| |
Collapse
|
4
|
Rehman AU, Bird JE, Faridi R, Shahzad M, Shah S, Lee K, Khan SN, Imtiaz A, Ahmed ZM, Riazuddin S, Santos-Cortez RLP, Ahmad W, Leal SM, Riazuddin S, Friedman TB. Mutational Spectrum of MYO15A and the Molecular Mechanisms of DFNB3 Human Deafness. Hum Mutat 2016; 37:991-1003. [PMID: 27375115 DOI: 10.1002/humu.23042] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2016] [Accepted: 06/26/2016] [Indexed: 12/17/2022]
Abstract
Deafness in humans is a common neurosensory disorder and is genetically heterogeneous. Across diverse ethnic groups, mutations of MYO15A at the DFNB3 locus appear to be the third or fourth most common cause of autosomal-recessive, nonsyndromic deafness. In 49 of the 67 exons of MYO15A, there are currently 192 recessive mutations identified, including 14 novel mutations reported here. These mutations are distributed uniformly across MYO15A with one enigmatic exception; the alternatively spliced giant exon 2, encoding 1,233 residues, has 17 truncating mutations but no convincing deafness-causing missense mutations. MYO15A encodes three distinct isoform classes, one of which is 395 kDa (3,530 residues), the largest member of the myosin superfamily of molecular motors. Studies of Myo15 mouse models that recapitulate DFNB3 revealed two different pathogenic mechanisms of hearing loss. In the inner ear, myosin 15 is necessary both for the development and the long-term maintenance of stereocilia, mechanosensory sound-transducing organelles that extend from the apical surface of hair cells. The goal of this Mutation Update is to provide a comprehensive review of mutations and functions of MYO15A.
Collapse
Affiliation(s)
- Atteeq U Rehman
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, 20892
| | - Jonathan E Bird
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, 20892
| | - Rabia Faridi
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, 20892.,Centre of Excellence in Molecular Biology, University of the Punjab, Lahore, 54550, Pakistan
| | - Mohsin Shahzad
- Department of Otorhinolaryngology Head & Neck Surgery, School of Medicine, University of Maryland, Baltimore, Maryland, 21201
| | - Sujay Shah
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, 20892
| | - Kwanghyuk Lee
- Center for Statistical Genetics, Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, 77030
| | - Shaheen N Khan
- Centre of Excellence in Molecular Biology, University of the Punjab, Lahore, 54550, Pakistan
| | - Ayesha Imtiaz
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, 20892
| | - Zubair M Ahmed
- Department of Otorhinolaryngology Head & Neck Surgery, School of Medicine, University of Maryland, Baltimore, Maryland, 21201
| | - Saima Riazuddin
- Department of Otorhinolaryngology Head & Neck Surgery, School of Medicine, University of Maryland, Baltimore, Maryland, 21201
| | - Regie Lyn P Santos-Cortez
- Center for Statistical Genetics, Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, 77030
| | - Wasim Ahmad
- Department of Biochemistry, Faculty of Biological Sciences, Quaid-i-Azam University, Islamabad, 45320, Pakistan
| | - Suzanne M Leal
- Center for Statistical Genetics, Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, 77030
| | - Sheikh Riazuddin
- Allama Iqbal Medical Research Centre, Jinnah Hospital Complex, University of Health Sciences, Lahore, 54550, Pakistan
| | - Thomas B Friedman
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Bethesda, Maryland, 20892.
| |
Collapse
|
5
|
Alamo L, Qi D, Wriggers W, Pinto A, Zhu J, Bilbao A, Gillilan RE, Hu S, Padrón R. Conserved Intramolecular Interactions Maintain Myosin Interacting-Heads Motifs Explaining Tarantula Muscle Super-Relaxed State Structural Basis. J Mol Biol 2016; 428:1142-1164. [PMID: 26851071 DOI: 10.1016/j.jmb.2016.01.027] [Citation(s) in RCA: 68] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Revised: 01/15/2016] [Accepted: 01/25/2016] [Indexed: 01/08/2023]
Abstract
Tarantula striated muscle is an outstanding system for understanding the molecular organization of myosin filaments. Three-dimensional reconstruction based on cryo-electron microscopy images and single-particle image processing revealed that, in a relaxed state, myosin molecules undergo intramolecular head-head interactions, explaining why head activity switches off. The filament model obtained by rigidly docking a chicken smooth muscle myosin structure to the reconstruction was improved by flexibly fitting an atomic model built by mixing structures from different species to a tilt-corrected 2-nm three-dimensional map of frozen-hydrated tarantula thick filament. We used heavy and light chain sequences from tarantula myosin to build a single-species homology model of two heavy meromyosin interacting-heads motifs (IHMs). The flexibly fitted model includes previously missing loops and shows five intramolecular and five intermolecular interactions that keep the IHM in a compact off structure, forming four helical tracks of IHMs around the backbone. The residues involved in these interactions are oppositely charged, and their sequence conservation suggests that IHM is present across animal species. The new model, PDB 3JBH, explains the structural origin of the ATP turnover rates detected in relaxed tarantula muscle by ascribing the very slow rate to docked unphosphorylated heads, the slow rate to phosphorylated docked heads, and the fast rate to phosphorylated undocked heads. The conservation of intramolecular interactions across animal species and the presence of IHM in bilaterians suggest that a super-relaxed state should be maintained, as it plays a role in saving ATP in skeletal, cardiac, and smooth muscles.
Collapse
Affiliation(s)
- Lorenzo Alamo
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas, Apartado 20632, Caracas 1020A, Venezuela.
| | - Dan Qi
- Key Laboratory of Genome Sciences and Information, Beijing Institute of Genomics, 1 Beichen West Road, Chaoyang District, Beijing 100101, China.
| | - Willy Wriggers
- Department of Mechanical and Aerospace Engineering, Old Dominion University, 5115 Hampton Boulevard, Norfolk, VA 23529, USA.
| | - Antonio Pinto
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas, Apartado 20632, Caracas 1020A, Venezuela.
| | - Jingui Zhu
- Key Laboratory of Genome Sciences and Information, Beijing Institute of Genomics, 1 Beichen West Road, Chaoyang District, Beijing 100101, China.
| | - Aivett Bilbao
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas, Apartado 20632, Caracas 1020A, Venezuela.
| | - Richard E Gillilan
- Macromolecular Diffraction Facility, Cornell High Energy Synchrotron Source, 161 Wilson Laboratory, Synchrotron Drive, Ithaca, NY 14853, USA.
| | - Songnian Hu
- Key Laboratory of Genome Sciences and Information, Beijing Institute of Genomics, 1 Beichen West Road, Chaoyang District, Beijing 100101, China.
| | - Raúl Padrón
- Centro de Biología Estructural, Instituto Venezolano de Investigaciones Científicas, Apartado 20632, Caracas 1020A, Venezuela.
| |
Collapse
|
6
|
Chantler PD. Scallop Adductor Muscles. ACTA ACUST UNITED AC 2016. [DOI: 10.1016/b978-0-444-62710-0.00004-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/07/2023]
|
7
|
Abstract
Vascular smooth muscle (VSM; see Table 1 for a list of abbreviations) is a heterogeneous biomaterial comprised of cells and extracellular matrix. By surrounding tubes of endothelial cells, VSM forms a regulated network, the vasculature, through which oxygenated blood supplies specialized organs, permitting the development of large multicellular organisms. VSM cells, the engine of the vasculature, house a set of regulated nanomotors that permit rapid stress-development, sustained stress-maintenance and vessel constriction. Viscoelastic materials within, surrounding and attached to VSM cells, comprised largely of polymeric proteins with complex mechanical characteristics, assist the engine with countering loads imposed by the heart pump, and with control of relengthening after constriction. The complexity of this smart material can be reduced by classical mechanical studies combined with circuit modeling using spring and dashpot elements. Evaluation of the mechanical characteristics of VSM requires a more complete understanding of the mechanics and regulation of its biochemical parts, and ultimately, an understanding of how these parts work together to form the machinery of the vascular tree. Current molecular studies provide detailed mechanical data about single polymeric molecules, revealing viscoelasticity and plasticity at the protein domain level, the unique biological slip-catch bond, and a regulated two-step actomyosin power stroke. At the tissue level, new insight into acutely dynamic stress-strain behavior reveals smooth muscle to exhibit adaptive plasticity. At its core, physiology aims to describe the complex interactions of molecular systems, clarifying structure-function relationships and regulation of biological machines. The intent of this review is to provide a comprehensive presentation of one biomachine, VSM.
Collapse
Affiliation(s)
- Paul H Ratz
- Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, Virginia, USA
| |
Collapse
|
8
|
Loop 2 of myosin is a force-dependent inhibitor of the rigor bond. J Muscle Res Cell Motil 2014; 35:143-52. [PMID: 24500136 DOI: 10.1007/s10974-014-9375-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2013] [Accepted: 01/21/2014] [Indexed: 10/25/2022]
Abstract
Myosin's actin-binding loop (loop 2) carries a charge opposite to that of its binding site on actin and is thought to play an important role in ionic interactions between the two molecules during the initial binding step. However, no subsequent role has been identified for loop 2 in actin-myosin binding. We used an optical trap to measure bond formation and bond rupture between actin and rigor heavy meromyosin when loaded perpendicular to the filament axis. We studied HMM with intact or proteolytically cleaved loop 2 at low and physiologic ionic strength. Here we show that the presence of intact loop 2 allows actomyosin bonds to form quickly and that they do so in a short-lived bound state. Increasing tensile load causes the transition to a long-lived state-the distinguishing behavior of a catch bond. When loop 2 was cleaved catch bond behavior was abrogated leaving only a long-lived state. These data suggest that in addition to its role in locating binding sites on actin, loop 2 is also a force-dependent inhibitor of the long-lived actomyosin complex. This may be important for reducing the duty ratio and increasing the shortening velocity of actomyosin at low forces.
Collapse
|
9
|
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.
Collapse
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.
| |
Collapse
|
10
|
The mechanical properties of Drosophila jump muscle expressing wild-type and embryonic Myosin isoforms. Biophys J 2010; 98:1218-26. [PMID: 20371321 DOI: 10.1016/j.bpj.2009.11.051] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2009] [Revised: 10/27/2009] [Accepted: 11/10/2009] [Indexed: 11/20/2022] Open
Abstract
Transgenic Drosophila are highly useful for structure-function studies of muscle proteins. However, our ability to mechanically analyze transgenically expressed mutant proteins in Drosophila muscles has been limited to the skinned indirect flight muscle preparation. We have developed a new muscle preparation using the Drosophila tergal depressor of the trochanter (TDT or jump) muscle that increases our experimental repertoire to include maximum shortening velocity (V(slack)), force-velocity curves and steady-state power generation; experiments not possible using indirect flight muscle fibers. When transgenically expressing its wild-type myosin isoform (Tr-WT) the TDT is equivalent to a very fast vertebrate muscle. TDT has a V(slack) equal to 6.1 +/- 0.3 ML/s at 15 degrees C, a steep tension-pCa curve, isometric tension of 37 +/- 3 mN/mm(2), and maximum power production at 26% of isometric tension. Transgenically expressing an embryonic myosin isoform in the TDT muscle increased isometric tension 1.4-fold, but decreased V(slack) 50% resulting in no significant difference in maximum power production compared to Tr-WT. Drosophila expressing embryonic myosin jumped <50% as far as Tr-WT that, along with comparisons to frog jump muscle studies, suggests fast muscle shortening velocity is relatively more important than high tension generation for Drosophila jumping.
Collapse
|
11
|
Zheng W. Multiscale modeling of structural dynamics underlying force generation and product release in actomyosin complex. Proteins 2010; 78:638-60. [PMID: 19790263 DOI: 10.1002/prot.22594] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
To decrypt the mechanistic basis of myosin motor function, it is essential to probe the conformational changes in actomyosin with high spatial and temporal resolutions. In a computational effort to meet this challenge, we have performed a multiscale modeling of the allosteric couplings and transition pathway of actomyosin complex by combining coarse-grained modeling of the entire complex with all-atom molecular dynamics simulations of the active site. Our modeling of allosteric couplings at the pre-powerstroke state has pinpointed key actin-activated couplings to distant myosin parts which are critical to force generation and the sequential release of phosphate and ADP. At the post-powerstroke state, we have identified isoform-dependent couplings which underlie the reciprocal coupling between actin binding and nucleotide binding in fast Myosin II, and load-dependent ADP release in Myosin V. Our modeling of transition pathway during powerstroke has outlined a clear sequence of structural events triggered by actin binding, which lead to subsequent force generation, twisting of central beta-sheet, and the sequential release of phosphate and ADP. Finally we have performed atomistic simulations of active-site dynamics based on an on-path "transition-state" myosin conformation, which has revealed significantly weakened coordination of phosphate by Switch II, and a disrupted key salt bridge between Switch I and II. Meanwhile, the coordination of MgADP by Switch I and P loop is less perturbed. As a result, the phosphate can be released prior to MgADP. This study has shed new lights on the controversy over the structural mechanism of actin-activated phosphate release and force generation in myosin motor.
Collapse
Affiliation(s)
- Wenjun Zheng
- Physics Department, University at Buffalo, Buffalo, New York 14260, USA.
| |
Collapse
|
12
|
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.
Collapse
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
| |
Collapse
|
13
|
Heintzelman MB, Enriquez ME. Myosin diversity in the diatom Phaeodactylum tricornutum. Cytoskeleton (Hoboken) 2010; 67:142-51. [PMID: 20217677 DOI: 10.1002/cm.20431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
This report describes the domain architecture of ten myosins cloned from the pennate diatom Phaeodactylum tricornutum. Several of the P. tricornutum myosins show similarity to myosins from the centric diatom Thalassiosira pseudonana as well as to one myosin from the oomycete Phytophthora ramorum. The P. tricornutum myosins, ranging in size from 126 kDa to over 250 kDa, all possess the canonical head, neck and tail domains common to most myosins, though variations in each of these domains is evident. Among the features distinguishing several of the diatom myosin head domains are N-terminal SH3-like domains, variations in or near the P-loop and Loop 1 regions close to the nucleotide binding pocket, and extended converter domains. Variations in the length of the neck domain or lever arm, defined by the light chain-binding IQ motifs, are apparent with the different diatom myosins predicted to contain from one to nine IQ motifs. Protein domains found within the P. tricornutum myosin tails include regions of coiled-coil structure, ankyrin repeats, CBS domain pairs, a PB1 domain, a kinase domain and a FYVE-finger motif. As many of these features have never before been characterized in myosins of any type, it is likely that these new diatom myosins will expand the repertoire of known myosin behaviors.
Collapse
Affiliation(s)
- Matthew B Heintzelman
- Program in Cell Biology and Biochemistry, Department of Biology, Bucknell University, Lewisburg, PA 17837, USA.
| | | |
Collapse
|
14
|
Functional diversity among a family of human skeletal muscle myosin motors. Proc Natl Acad Sci U S A 2009; 107:1053-8. [PMID: 20080549 DOI: 10.1073/pnas.0913527107] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Human skeletal muscle fibers express five highly conserved type-II myosin heavy chain (MyHC) genes in distinct spatial and temporal patterns. In addition, the human genome contains an intact sixth gene, MyHC-IIb, which is thought under most circumstances not to be expressed. The physiological and biochemical properties of individual muscle fibers correlate with the predominantly expressed MyHC isoform, but a functional analysis of homogenous skeletal muscle myosin isoforms has not been possible. This is due to the difficulties of separating the multiple isoforms usually coexpressed in muscle fibers, as well as the lack of an expression system that produces active recombinant type II skeletal muscle myosin. In this study we describe a mammalian muscle cell expression system and the functional analysis of all six recombinant human type II skeletal muscle myosin isoforms. The diverse biochemical activities and actin-filament velocities of these myosins indicate that they likely have distinct functions in muscle. Our data also show that ATPase activity and motility are generally correlated for human skeletal muscle myosins. The exception, MyHC-IIb, encodes a protein that is high in ATPase activity but slow in motility; this is the first functional analysis of the protein from this gene. In addition, the developmental isoforms, hypothesized to have low ATPase activity, were indistinguishable from adult-fast MyHC-IIa and the specialized MyHC-Extraocular isoform, that was predicted to be the fastest of all six isoforms but was functionally similar to the slower isoforms.
Collapse
|
15
|
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]
|
16
|
Yang C, Ramanath S, Kronert WA, Bernstein SI, Maughan DW, Swank DM. Alternative versions of the myosin relay domain differentially respond to load to influence Drosophila muscle kinetics. Biophys J 2008; 95:5228-37. [PMID: 18805920 PMCID: PMC2586575 DOI: 10.1529/biophysj.108.136192] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2008] [Accepted: 08/19/2008] [Indexed: 11/18/2022] Open
Abstract
We measured the influence of alternative versions of the Drosophila melanogaster myosin heavy chain relay domain on muscle mechanical properties. We exchanged relay domain regions (encoded by alternative versions of exon 9) between an embryonic (EMB) isoform and the indirect flight muscle isoform (IFI) of myosin. Previously, we observed no effect of exchanging the EMB relay domain region into the flight muscle isoform (IFI-9b) on in vitro actin motility velocity or solution ATPase measurements compared to IFI. However, in indirect flight muscle fibers, IFI-9b exhibited decreased maximum power generation (P(max)) and optimal frequency of power generation (f(max)) to 70% and 83% of IFI fiber values. The decrease in muscle performance reduced the flight ability and wing-beat frequency of IFI-9b Drosophila compared to IFI Drosophila. Previously, we found that exchanging the flight muscle specific relay domain into the EMB isoform (EMB-9a) prevented actin movement in the in vitro motility assay compared to EMB, which does support actin movement. However, in indirect flight muscle fibers EMB-9a was a highly effective motor, increasing P(max) and f(max) 2.5-fold and 1.4-fold, respectively, compared to fibers expressing EMB. We propose that the oscillatory load EMB-9a experiences in the muscle fiber reduces a high activation energy barrier between two strongly bound states of the cross-bridge cycle, thereby promoting cross-bridge cycling. The IFI relay domain's enhanced sensitivity to load increases cross-bridge kinetics, whereas the EMB version is less load-sensitive.
Collapse
Affiliation(s)
- Chaoxing Yang
- Department of Biology and Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute, Troy, New York, USA
| | | | | | | | | | | |
Collapse
|
17
|
Hooper SL, Hobbs KH, Thuma JB. Invertebrate muscles: thin and thick filament structure; molecular basis of contraction and its regulation, catch and asynchronous muscle. Prog Neurobiol 2008; 86:72-127. [PMID: 18616971 PMCID: PMC2650078 DOI: 10.1016/j.pneurobio.2008.06.004] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2007] [Revised: 05/08/2008] [Accepted: 06/12/2008] [Indexed: 11/26/2022]
Abstract
This is the second in a series of canonical reviews on invertebrate muscle. We cover here thin and thick filament structure, the molecular basis of force generation and its regulation, and two special properties of some invertebrate muscle, catch and asynchronous muscle. Invertebrate thin filaments resemble vertebrate thin filaments, although helix structure and tropomyosin arrangement show small differences. Invertebrate thick filaments, alternatively, are very different from vertebrate striated thick filaments and show great variation within invertebrates. Part of this diversity stems from variation in paramyosin content, which is greatly increased in very large diameter invertebrate thick filaments. Other of it arises from relatively small changes in filament backbone structure, which results in filaments with grossly similar myosin head placements (rotating crowns of heads every 14.5 nm) but large changes in detail (distances between heads in azimuthal registration varying from three to thousands of crowns). The lever arm basis of force generation is common to both vertebrates and invertebrates, and in some invertebrates this process is understood on the near atomic level. Invertebrate actomyosin is both thin (tropomyosin:troponin) and thick (primarily via direct Ca(++) binding to myosin) filament regulated, and most invertebrate muscles are dually regulated. These mechanisms are well understood on the molecular level, but the behavioral utility of dual regulation is less so. The phosphorylation state of the thick filament associated giant protein, twitchin, has been recently shown to be the molecular basis of catch. The molecular basis of the stretch activation underlying asynchronous muscle activity, however, remains unresolved.
Collapse
Affiliation(s)
- Scott L. Hooper
- Neuroscience Program Department of Biological Sciences Ohio University Athens, OH 45701 614 593-0679 (voice) 614 593-0687 (FAX)
| | - Kevin H. Hobbs
- Neuroscience Program Department of Biological Sciences Ohio University Athens, OH 45701 614 593-0679 (voice) 614 593-0687 (FAX)
| | - Jeffrey B. Thuma
- Neuroscience Program Department of Biological Sciences Ohio University Athens, OH 45701 614 593-0679 (voice) 614 593-0687 (FAX)
| |
Collapse
|
18
|
Elworthy S, Hargrave M, Knight R, Mebus K, Ingham PW. Expression of multiple slow myosin heavy chain genes reveals a diversity of zebrafish slow twitch muscle fibres with differing requirements for Hedgehog and Prdm1 activity. Development 2008; 135:2115-26. [PMID: 18480160 DOI: 10.1242/dev.015719] [Citation(s) in RCA: 117] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The zebrafish embryo develops a series of anatomically distinct slow twitch muscle fibres that characteristically express genes encoding lineage-specific isoforms of sarcomeric proteins such as MyHC and troponin. We show here that different subsets of these slow fibres express distinct members of a tandem array of slow MyHC genes. The first slow twitch muscle fibres to differentiate, which are specified by the activity of the transcription factor Prdm1 (also called Ubo or Blimp1) in response to Hedgehog (Hh) signalling, express the smyhc1 gene. Subsequently, secondary slow twitch fibres differentiate in most cases independently of Hh activity. We find that although some of these later-forming fibres also express smyhc1, others express smyhc2 or smyhc3. We show that the smyhc1-positive fibres express the ubo (prdm1) gene and adopt fast twitch fibre characteristics in the absence of Prdm1 activity, whereas those that do not express smyhc1 can differentiate independently of Prdm1 function. Conversely, some smyhc2-expressing fibres, although independent of Prdm1 function, require Hh activity to form. The adult trunk slow fibres express smyhc2 and smyhc3, but lack smyhc1 expression. The different slow fibres in the craniofacial muscles variously express smyhc1, smyhc2 and smyhc3, and all differentiate independently of Prdm1.
Collapse
Affiliation(s)
- Stone Elworthy
- MRC Centre for Developmental and Biomedical Genetics and Department of Biomedical Science, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | | | | | | | | |
Collapse
|
19
|
Kim KY, Kawamoto S, Bao J, Sellers JR, Adelstein RS. The B2 alternatively spliced isoform of nonmuscle myosin II-B lacks actin-activated MgATPase activity and in vitro motility. Biochem Biophys Res Commun 2007; 369:124-34. [PMID: 18060863 DOI: 10.1016/j.bbrc.2007.11.108] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2007] [Accepted: 11/15/2007] [Indexed: 10/24/2022]
Abstract
We report the initial biochemical characterization of an alternatively spliced isoform of nonmuscle heavy meromyosin (HMM) II-B2 and compare it with HMM II-B0, the nonspliced isoform. HMM II-B2 is the HMM derivative of an alternatively spliced isoform of endogenous nonmuscle myosin (NM) II-B, which has 21-amino acids inserted into loop 2, near the actin-binding region. NM II-B2 is expressed in the Purkinje cells of the cerebellum as well as in other neuronal cells [X. Ma, S. Kawamoto, J. Uribe, R.S. Adelstein, Function of the neuron-specific alternatively spliced isoforms of nonmuscle myosin II-B during mouse brain development, Mol. Biol. Cell 15 (2006) 2138-2149]. In contrast to any of the previously described isoforms of NM II (II-A, II-B0, II-B1, II-C0 and II-C1) or to smooth muscle myosin, the actin-activated MgATPase activity of HMM II-B2 is not significantly increased from a low, basal level by phosphorylation of the 20kDa myosin light chain (MLC-20). Moreover, although HMM II-B2 can bind to actin in the absence of ATP and is released in its presence, it cannot propel actin in the sliding actin filament assay following MLC-20 phosphorylation. Unlike HMM II-B2, the actin-activated MgATPase activity of a chimeric HMM with the 21-amino acid II-B2 sequence inserted into the homologous location in the heavy chain of HMM II-C is increased following MLC-20 phosphorylation. This indicates that the effect of the II-B2 insert is myosin heavy chain specific.
Collapse
Affiliation(s)
- Kye-Young Kim
- Laboratory of Molecular Cardiology, National Heart, Lung, and Blood Institute, National Institutes of Health Bethesda, MD 20892, USA
| | | | | | | | | |
Collapse
|
20
|
Krenz M, Sadayappan S, Osinska HE, Henry JA, Beck S, Warshaw DM, Robbins J. Distribution and structure-function relationship of myosin heavy chain isoforms in the adult mouse heart. J Biol Chem 2007; 282:24057-64. [PMID: 17575272 DOI: 10.1074/jbc.m704574200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The two cardiac myosin heavy chain isoforms, alpha and beta, exhibit distinct functional characteristics and therefore may be distributed regionally within the heart to match the functional demands of a specific region. In adult mouse hearts, which predominantly express alpha-myosin heavy chain, we observed high concentrations of beta-myosin in distinct areas such as at the tip of papillary muscles and at the base close to the valvular annulus. In light of these distinct distribution patterns of the myosin isoforms, we subsequently explored the isoform-specific structure-function relationships of the myosins. The alpha- and beta-isoforms are 93% identical in amino acid sequence, but it remains unclear which of the nonidentical residues determines isoform functionality. We hypothesized that residues situated within or close to the actin-binding interface of the myosin head influence actin binding and thereby modulate actin-activated ATPase activity. A chimeric myosin was created containing beta-sequence from amino acid 417 to 682 within the alpha-backbone. In mice, approximately 70% of the endogenous cardiac protein was replaced with the chimeric myosin. Myofibrils containing chimeric myosin exhibited ATPase activities that were depressed to the levels observed in hearts expressing approximately 70% beta-myosin. In vitro motility assays showed that the actin filament sliding velocity generated by chimeric myosin was similar to that of alpha-myosin, almost twice the velocities observed with beta-myosin. These data indicate that this large domain sequence switch conferred beta-like actin-activated ATPase activities to the chimeric myosin, suggesting that this region is responsible for the distinct hydrolytic properties of these myosin isoforms.
Collapse
Affiliation(s)
- Maike Krenz
- Division of Molecular Cardiovascular Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229, USA
| | | | | | | | | | | | | |
Collapse
|
21
|
Swank DM, Braddock J, Brown W, Lesage H, Bernstein SI, Maughan DW. An alternative domain near the ATP binding pocket of Drosophila myosin affects muscle fiber kinetics. Biophys J 2006; 90:2427-35. [PMID: 16399836 PMCID: PMC1403199 DOI: 10.1529/biophysj.105.075184] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We examined the importance of alternative versions of a region near the ATP binding site of Drosophila myosin heavy chain for muscle mechanical properties. Previously, we exchanged two versions of this region (encoded by alternative exon 7s) between the indirect flight muscle myosin isoform (IFI) and an embryonic myosin isoform (EMB) and found, surprisingly, that in vitro solution actin-activated ATPase rates were increased (higher Vmax) by both exon exchanges. Here we examined the effect of increased ATPase rate on indirect flight muscle (IFM) fiber mechanics and Drosophila locomotion. IFM expressing EMB with the exon 7a domain replaced by the IFM specific exon 7d domain (EMB-7d) exhibited 3.2-fold greater maximum oscillatory power (Pmax) and 1.5-fold greater optimal frequency of power generation (fmax) versus fibers expressing EMB. In contrast, IFM expressing IFI with the exon 7d region replaced by the EMB exon 7a region (IFI-7a), showed no change in Pmax, fmax, step response, or isometric muscle properties compared to native IFI fibers. A slight decrement in IFI-7a flight ability was observed, suggesting a negative influence of the increased ATPase rate on Drosophila locomotion, perhaps due to energy supply constraints. Our results show that exon 7 plays a substantial role in establishing fiber speed and flight performance, and that the limiting step that sets ATPase rate in Drosophila myosin has little to no direct influence in setting fmax for fast muscle fiber types.
Collapse
Affiliation(s)
- Douglas M Swank
- Department of Biology and Center for Biotechnology, Rensselaer Polytechnic Institute, Troy, New York 12180, USA.
| | | | | | | | | | | |
Collapse
|
22
|
Chapter 4 Scallop adductor muscles: Structure and function. SCALLOPS: BIOLOGY, ECOLOGY AND AQUACULTURE 2006. [DOI: 10.1016/s0167-9309(06)80031-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
|
23
|
Clark R, Ansari MA, Dash S, Geeves MA, Coluccio LM. Loop 1 of transducer region in mammalian class I myosin, Myo1b, modulates actin affinity, ATPase activity, and nucleotide access. J Biol Chem 2005; 280:30935-42. [PMID: 15980431 DOI: 10.1074/jbc.m504698200] [Citation(s) in RCA: 29] [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
Loop 1, a flexible surface loop in the myosin motor domain, comprises in part the transducer region that lies near the nucleotide-binding site and is proposed from structural studies to be responsible for the kinetic tuning of product release following ATP hydrolysis (1). Biochemical studies have shown that loop 1 affects the affinity of actin-myosin-II for ADP, motility and the V(max) of the actin-activated Mg2+-ATPase activity, possibly through P(i) release (2-8). To test the influence of loop 1 on the mammalian class I myosin, Myo1b, chimeric molecules in which (i) loop 1 of a truncated form of Myo1b, Myo1b1IQ, was replaced with either loop 1 from other myosins; (ii) loop 1 was replaced with glycine; or (iii) some amino acids in the loop were substituted with alanine and were expressed in baculovirus, and their interactions with actin and nucleotide were evaluated. The steady-state actin-activated ATPase activity; rate of ATP-induced dissociation of actin from Myo1b1IQ; rate of ADP release from actin-Myo1b1IQ; and the affinity of actin for Myo1b1IQ and Myo1b1IQ.ADP differed in the chimeras versus wild type, indicating that loop 1 has a much wider range of effects on the coupling between actin and nucleotide binding events than previously thought. In particular, the biphasic ATP-induced dissociation of actin from actin-Myo1b1IQ was significantly altered in the chimeras. This provided evidence that loop 1 contributes to the accessibility of the nucleotide pocket and is involved in the integration of information from the actin-, nucleotide-, gamma-P(i)-, and calmodulin-binding sites and predicts that loop 1 modulates the load dependence of the motor.
Collapse
Affiliation(s)
- Richard Clark
- Department of Biosciences, University of Kent at Canterbury, Canterbury, Kent CT2 7NJ, United Kingdom
| | | | | | | | | |
Collapse
|
24
|
Abstract
Protein engineering and design provide excellent tools to investigate the principles by which particular structural features relate to the mechanisms that underlie the biological function of a protein. In addition to studies aimed at dissecting the communication pathways within enzymes, recent advances in protein engineering approaches make it possible to generate enzymes with increased catalytic efficiency and specifically altered or newly introduced functions. Here, two approaches using state-of-the-art protein design and engineering are described in detail to demonstrate how key features of the myosin motor can be changed in a specific and predictable manner. First, it is shown how replacement of an actin-binding surface loop with synthetic sequences, whose flexibility and charge density is varied, can be employed to manipulate the actin affinity, the catalytic activity and the efficiency of coupling between actin- and nucleotide-binding sites of myosin motor constructs. Then the use of pre-existing molecular building blocks, which are derived from unrelated proteins, is described for manipulating the velocity and even the direction of movement of recombinant myosins.
Collapse
Affiliation(s)
- Dietmar J Manstein
- Institut für Biophysikalische Chemie, Medizinische Hochschule Hannover, OE 4350, Carl-Neuberg-Strasse 1, D-30623 Hannover, Germany.
| |
Collapse
|
25
|
Alpert NR, Mohiddin SA, Tripodi D, Jacobson-Hatzell J, Vaughn-Whitley K, Brosseau C, Warshaw DM, Fananapazir L. Molecular and phenotypic effects of heterozygous, homozygous, and compound heterozygote myosin heavy-chain mutations. Am J Physiol Heart Circ Physiol 2004; 288:H1097-102. [PMID: 15528230 DOI: 10.1152/ajpheart.00650.2004] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Autosomal dominant familial hypertrophic cardiomyopathy (FHC) has variable penetrance and phenotype. Heterozygous mutations in MYH7 encoding beta-myosin heavy chain are the most common causes of FHC, and we proposed that "enhanced" mutant actin-myosin function is the causative molecular abnormality. We have studied individuals from families in which members have two, one, or no mutant MYH7 alleles to examine for dose effects. In one family, a member homozygous for Lys207Gln had cardiomyopathy complicated by left ventricular dilatation, systolic impairment, atrial fibrillation, and defibrillator interventions. Only one of five heterozygous relatives had FHC. Leu908Val and Asp906Gly mutations were detected in a second family in which penetrance for Leu908Val heterozygotes was 46% (21/46) and 25% (3/12) for Asp906Gly. Despite the low penetrance, hypertrophy was severe in several heterozygotes. Two individuals with both mutations developed severe FHC. The velocities of actin translocation (V(actin)) by mutant and wild-type (WT) myosins were compared in the in vitro motility assay. Compared with WT/WT, V(actin) was 34% faster for WT/D906G and 21% for WT/L908V. Surprisingly V(actin) for Leu908Val/Asp906Gly and Lys207Gln/Lys207Gln mutants were similar to WT. The apparent enhancement of mechanical performance with mutant/WT myosin was not observed for mutant/mutant myosin. This suggests that V(actin) may be a poor predictor of disease penetrance or severity and that power production may be more appropriate, or that the limited availability of double mutant patients prohibits any definitive conclusions. Finally, severe FHC in heterozygous individuals can occur despite very low penetrance, suggesting these mutations alone are insufficient to cause FHC and that uncharacterized modifying mechanisms exert powerful influences.
Collapse
Affiliation(s)
- Norman R Alpert
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont, USA
| | | | | | | | | | | | | | | |
Collapse
|
26
|
Swank DM, Kronert WA, Bernstein SI, Maughan DW. Alternative N-terminal regions of Drosophila myosin heavy chain tune muscle kinetics for optimal power output. Biophys J 2004; 87:1805-14. [PMID: 15345559 PMCID: PMC1304585 DOI: 10.1529/biophysj.103.032078] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2003] [Accepted: 06/03/2004] [Indexed: 11/18/2022] Open
Abstract
We assessed the influence of alternative versions of a region near the N-terminus of Drosophila myosin heavy chain on muscle mechanical properties. Previously, we exchanged N-terminal regions (encoded by alternative exon 3s) between an embryonic (EMB) isoform and the indirect flight muscle isoform (IFI) of myosin, and demonstrated that it influences solution ATPase rates and in vitro actin sliding velocity. Because each myosin is expressed in Drosophila indirect flight muscle, in the absence of other myosin isoforms, this allows for muscle mechanical and whole organism locomotion assays. We found that exchanging the flight muscle specific exon 3 region into the embryonic isoform (EMB-3b) increased maximum power generation (P(max)) and optimal frequency of power generation (f(max)) threefold and twofold compared to fibers expressing EMB, whereas exchanging the embryonic exon 3 region into the flight muscle isoform (IFI-3a) decreased P(max) and f(max) to approximately 80% of IFI fiber values. Drosophila expressing IFI-3a exhibited a reduced wing beat frequency compared to flies expressing IFI, which optimized power generation from their kinetically slowed flight muscle. However, the slower wing beat frequency resulted in a substantial loss of aerodynamic power as manifest in decreased flight performance of IFI-3a compared to IFI. Thus the N-terminal region is important in tuning myosin kinetics to match muscle speed for optimal locomotory performance.
Collapse
Affiliation(s)
- Douglas M Swank
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont 05405, USA.
| | | | | | | |
Collapse
|
27
|
Andruchov O, Andruchova O, Wang Y, Galler S. Kinetic properties of myosin heavy chain isoforms in mouse skeletal muscle: comparison with rat, rabbit, and human and correlation with amino acid sequence. Am J Physiol Cell Physiol 2004; 287:C1725-32. [PMID: 15306546 DOI: 10.1152/ajpcell.00255.2004] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Stretch activation kinetics were investigated in skinned mouse skeletal muscle fibers of known myosin heavy chain (MHC) isoform content to assess kinetic properties of different myosin heads while generating force. The time to peak of stretch-induced delayed force increase (t(3)) was strongly correlated with MHC isoforms [t(3) given in ms for fiber types containing specified isoforms; means +/- SD with n in parentheses: MHCI 680 +/- 108 (13), MHCIIa 110.5 +/- 10.7 (23), MHCIIx(d) 46.2 +/- 5.2 (20), MHCIIb 23.5 +/- 3.3 (76)]. This strong correlation suggests different kinetics of force generation of different MHC isoforms in the following order:MHCIIb > MHCIIx(d) > MHCIIa >> MHCI. For rat, rabbit, and human skeletal muscles the same type of correlation was found previously. The kinetics decreases slightly with increasing body mass. Available amino acid sequences were aligned to quantify the structural variability of MHC isoforms of different animal species. The variation in t(3) showed a correlation with the structural variability of specific actin-binding loops (so-called loop 2 and loop 3) of myosin heads (r = 0.74). This suggests that alterations of amino acids in these loops contribute to the different kinetics of myosin heads of various MHC isoforms.
Collapse
Affiliation(s)
- Oleg Andruchov
- Department of Cell Biology, University of Salzburg, Hellbrunnerstrasse 34, A-5020 Salzburg, Austria
| | | | | | | |
Collapse
|
28
|
Palmer BM, Fishbaugher DE, Schmitt JP, Wang Y, Alpert NR, Seidman CE, Seidman JG, VanBuren P, Maughan DW. Differential cross-bridge kinetics of FHC myosin mutations R403Q and R453C in heterozygous mouse myocardium. Am J Physiol Heart Circ Physiol 2004; 287:H91-9. [PMID: 15001446 DOI: 10.1152/ajpheart.01015.2003] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The kinetic effects of the cardiac myosin point mutations R403Q and R453C, which underlie lethal forms of familial hypertrophic cardiomyopathy (FHC), were assessed using isolated myosin and skinned strips taken from heterozygous (R403Q/+ and R453C/+) male mouse hearts. Compared with wild-type (WT) mice, actin-activated ATPase was increased by 38% in R403Q/+ and reduced by 45% in R453C/+, maximal velocity of regulated thin filament ( VRTF) in the in vitro motility assay was increased by 8% in R403Q/+ and was not different in R453C/+, myosin concentration at half-maximal VRTF was reduced by 30% in R403Q/+ and not different in R453C/+, and the characteristic frequency for oscillatory work production ( b frequency), determined by sinusoidal analysis in the skinned strip at maximal calcium activation, was 27% lower in R403Q/+ and 18% higher in R453C/+. The calcium sensitivity for isometric tension in the skinned strip was not different in R403Q/+ (pCa50 5.64 ± 0.02) and significantly enhanced in R453C/+ (5.82 ± 0.03) compared with WT (5.58 ± 0.02). We conclude that isolated myosin and skinned strips of R403Q/+ and R453C/+ myocardium show marked differences in cross-bridge kinetic parameters and in calcium sensitivity of force production that indicate different functional roles associated with the location of each point mutation at the molecular level.
Collapse
Affiliation(s)
- Bradley M Palmer
- Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405, USA.
| | | | | | | | | | | | | | | | | |
Collapse
|
29
|
Abstract
Myosin V is molecular motor that is capable of moving processively along actin filaments. The kinetics of monomeric myosin V containing a single IQ domain (MV 1IQ) differ from nonprocessive myosin II in that actin affinity is higher, phosphate release is extremely rapid, and ADP release is rate-limiting. We generated two mutants of myosin V by altering loop 2, a surface loop in the actin-binding region thought to alter actin affinity and phosphate release in myosin II, to determine the role that this loop plays in the kinetic tuning of myosin V. The loop 2 mutants altered the apparent affinity for actin (K(ATPase)) without altering the maximum ATPase rate (V(MAX)). Transient kinetic analysis determined that the rate of binding to actin, as well as the affinity for actin, was dependent on the net positive charge of loop 2, while other steps in the ATPase cycle were unchanged. The maximum rate of phosphate release was unchanged, but the affinity for actin in the M.ADP.Pi-state was dramatically altered by the mutations in loop 2. Thus, loop 2 is important for allowing myosin V to bind to actin with a relatively high affinity in the weak binding states but does not play a direct role in the product release steps. The ability to maintain a high affinity for actin in the weak binding states may prevent diffusion away from the actin filament and increase the degree of processive motion of myosin V.
Collapse
Affiliation(s)
- Christopher M Yengo
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6085, USA
| | | |
Collapse
|
30
|
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.
Collapse
Affiliation(s)
- Katalin Ajtai
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, Minnesota 55905, USA
| | | | | | | | | |
Collapse
|
31
|
Joel PB, Sweeney HL, Trybus KM. Addition of lysines to the 50/20 kDa junction of myosin strengthens weak binding to actin without affecting the maximum ATPase activity. Biochemistry 2003; 42:9160-6. [PMID: 12885250 DOI: 10.1021/bi034415j] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Much interest has centered on two surface loops in the motor domain to explain the differences in enzymatic and mechanical properties of myosin isoforms. We showed that two invariant lysines at the C-terminal end of loop 2, which is part of the actin-binding interface, are required to obtain actin activation [Joel et al. (2001) J. Biol. Chem. 276, 2998-3003]. Here we investigate the effects of increasing positive charge in the variable portion of loop 2 of smooth muscle heavy meromyosin (smHMM). Increasing the net positive charge by +4 increased the affinity for actin in the presence and absence of ATP. The K(m) for actin-activated ATPase activity decreased 15-fold, but V(max) was unchanged, showing that "weak binding" of myosin for actin can be significantly strengthened without increasing the rate-limiting step for V(max). The mutant HMM had slower rates of in vitro motility and ADP release compared to WT HMM. ADP release and motility, which were both salt-dependent, correlated linearly with each other. Loop 2 thus plays a major role in setting the affinity for actin but also affects ADP release and motility. Because the actin- and nucleotide-binding regions communicate, mutations to one region can impact multiple facets of myosin's mechanical and enzymatic properties.
Collapse
Affiliation(s)
- Peteranne B Joel
- Department of Molecular Physiology and Biophysics, University of Vermont College of Medicine, Burlington, Vermont 05405-0068, USA
| | | | | |
Collapse
|
32
|
Swank DM, Knowles AF, Kronert WA, Suggs JA, Morrill GE, Nikkhoy M, Manipon GG, Bernstein SI. Variable N-terminal regions of muscle myosin heavy chain modulate ATPase rate and actin sliding velocity. J Biol Chem 2003; 278:17475-82. [PMID: 12606545 DOI: 10.1074/jbc.m212727200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We integratively assessed the function of alternative versions of a region near the N terminus of Drosophila muscle myosin heavy chain (encoded by exon 3a or 3b). We exchanged the alternative exon 3 regions between an embryonic isoform and the indirect flight muscle isoform. Each chimeric myosin was expressed in Drosophila indirect flight muscle, in the absence of other myosin isoforms, allowing for purified protein analysis and whole organism locomotory studies. The flight muscle isoform generates higher in vitro actin sliding velocity and solution ATPase rates than the embryonic isoform. Exchanging the embryonic exon 3 region into the flight muscle isoform decreased ATPase rates to embryonic levels but did not affect actin sliding velocity or flight muscle ultrastructure. Interestingly, this swap only slightly impaired flight ability. Exchanging the flight muscle-specific exon 3 region into the embryonic isoform increased actin sliding velocity 3-fold and improved indirect flight muscle ultrastructure integrity but failed to rescue the flightless phenotype of flies expressing embryonic myosin. These results suggest that the two structural versions of the exon 3 domain independently influence the kinetics of at least two steps of the actomyosin cross-bridge cycle.
Collapse
Affiliation(s)
- Douglas M Swank
- Biology Department and Molecular Biology Institute, San Diego State University, San Diego, California 92182-4614, USA.
| | | | | | | | | | | | | | | |
Collapse
|
33
|
Krenz M, Sanbe A, Bouyer-Dalloz F, Gulick J, Klevitsky R, Hewett TE, Osinska HE, Lorenz JN, Brosseau C, Federico A, Alpert NR, Warshaw DM, Perryman MB, Helmke SM, Robbins J. Analysis of myosin heavy chain functionality in the heart. J Biol Chem 2003; 278:17466-74. [PMID: 12626511 DOI: 10.1074/jbc.m210804200] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Comparison of mammalian cardiac alpha- and beta-myosin heavy chain isoforms reveals 93% identity. To date, genetic methodologies have effected only minor switches in the mammalian cardiac myosin isoforms. Using cardiac-specific transgenesis, we have now obtained major myosin isoform shifts and/or replacements. Clusters of non-identical amino acids are found in functionally important regions, i.e. the surface loops 1 and 2, suggesting that these structures may regulate isoform-specific characteristics. Loop 1 alters filament sliding velocity, whereas Loop 2 modulates actin-activated ATPase rate in Dictyostelium myosin, but this remains untested in mammalian cardiac myosins. Alpha --> beta isoform switches were engineered into mouse hearts via transgenesis. To assess the structural basis of isoform diversity, chimeric myosins in which the sequences of either Loop 1+Loop 2 or Loop 2 of alpha-myosin were exchanged for those of beta-myosin were expressed in vivo. 2-fold differences in filament sliding velocity and ATPase activity were found between the two isoforms. Filament sliding velocity of the Loop 1+Loop 2 chimera and the ATPase activities of both loop chimeras were not significantly different compared with alpha-myosin. In mouse cardiac isoforms, myosin functionality does not depend on Loop 1 or Loop 2 sequences and must lie partially in other non-homologous residues.
Collapse
Affiliation(s)
- Maike Krenz
- Cincinnati Children's Hospital Medical Center, The Children's Hospital Research Foundation, MLC 7020, Cincinnati, Ohio 45229-3039, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
34
|
Swank DM, Knowles AF, Suggs JA, Sarsoza F, Lee A, Maughan DW, Bernstein SI. The myosin converter domain modulates muscle performance. Nat Cell Biol 2002; 4:312-6. [PMID: 11901423 DOI: 10.1038/ncb776] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Myosin is the molecular motor that powers muscle contraction as a result of conformational changes during its mechanochemical cycle. We demonstrate that the converter, a compact structural domain that differs in sequence between Drosophila melanogaster myosin isoforms, dramatically influences the kinetic properties of myosin and muscle fibres. Transgenic replacement of the converter in the fast indirect flight muscle with the converter from an embryonic muscle slowed muscle kinetics, forcing a compensatory reduction in wing beat frequency to sustain flight. Conversely, replacing the embryonic converter with the flight muscle converter sped up muscle kinetics and increased maximum power twofold, compared to flight muscles expressing the embryonic myosin isoform. The substitutions also dramatically influenced in vitro actin sliding velocity, suggesting that the converter modulates a rate-limiting step preceding cross-bridge detachment. Our integrative analysis demonstrates that isoform-specific differences in the myosin converter allow different muscle types to meet their specific locomotion demands.
Collapse
Affiliation(s)
- Douglas M Swank
- Department of Biology, Molecular Biology Institute, and the Heart Institute, San Diego State University, San Diego, California 92182-4614, USA.
| | | | | | | | | | | | | |
Collapse
|
35
|
Babu GJ, Loukianov E, Loukianova T, Pyne GJ, Huke S, Osol G, Low RB, Paul RJ, Periasamy M. Loss of SM-B myosin affects muscle shortening velocity and maximal force development. Nat Cell Biol 2001; 3:1025-9. [PMID: 11715025 DOI: 10.1038/ncb1101-1025] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
We used an exon-specific gene-targeting strategy to generate a mouse model deficient only in the SM-B myosin isoform. Here we show that deletion of exon-5B (specific for SM-B) in the gene for the heavy chain of smooth muscle myosin results in a complete loss of SM-B myosin and switching of splicing to the SM-A isoform, without affecting SM1 and SM2 myosin content. Loss of SM-B myosin does not affect survival or cause any overt smooth muscle pathology. Physiological analysis reveals that absence of SM-B myosin results in a significant decrease in maximal force generation and velocity of shortening in smooth muscle tissues. This is the first in vivo study to demonstrate a functional role for the SM-B myosin isoform. We conclude that the extra seven-residue insert in the surface loop 1 of SM-B myosin is a critical determinant of crossbridge cycling and velocity of shortening.
Collapse
Affiliation(s)
- G J Babu
- Department of Physiology and Cell Biology, College of Medicine and Public Health, The Ohio State University, 304 Hamilton Hall, 1645 Neil Avenue, Columbus, Ohio 43210, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
36
|
Ajtai K, Garamszegi SP, Park S, Velazquez Dones AL, Burghardt TP. Structural characterization of beta-cardiac myosin subfragment 1 in solution. Biochemistry 2001; 40:12078-93. [PMID: 11580283 DOI: 10.1021/bi0112098] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
beta-cardiac myosin subfragment 1 (betaS1) tertiary structure and dynamics were characterized with proteolytic digestion, nucleotide analogue trapping kinetics, and intrinsic fluorescence changes accompanying nucleotide binding. Proteolysis of betaS1 produces the 25, 50, and 20 kDa fragments and a new cut within the 50-kDa fragment at Arg369. F-actin inhibits cleavage of the 50-kDa fragment and fails to inhibit cleavage at the 50/20 kDa junction, suggesting betaS1 presents an actoS1 conformation fundamentally different from skeletal S1. Time-dependent changes in Mg(2+)-ATPase accompanying proteolysis identifies cleavage points that lie within the energy transduction pathway. The nucleotide analogue trapping kinetics reveal the presence of a reversible weakly actin attached state. Comparison of nucleotide analogue induced betaS1 structures with the transient structures occurring during ATPase indicates analogue induced and transient structures are in a one-to-one correspondence. Tryptophan fluorescence enhancement accompanies the binding or trapping of nucleotide or nucleotide analogues. Isolation of Trp508 fluorescence shows it is an ATP-sensitive tryptophan and that its vicinity changes conformation sequentially with the transient intermediates accompanying ATPase. These studies elucidate energy transduction and suggest how mutations of betaS1 implicated in disease might undermine function, stability, or efficiency.
Collapse
Affiliation(s)
- K Ajtai
- Department of Biochemistry and Molecular Biology, Mayo Foundation, 200 First Street SW, Rochester, Minnesota 55905, USA
| | | | | | | | | |
Collapse
|
37
|
Abstract
Recent experiments, drawing upon single-molecule, solution kinetic and structural techniques, have clarified our mechanistic understanding of class V myosins. The findings of the past two years can be summarized as follows: (1) Myosin V is a highly efficient processive motor, surpassing even conventional kinesin in the distance that individual molecules can traverse. (2) The kinetic scheme underlying ATP turnover resembles those of myosins I and II but with rate constants tuned to favor strong binding to actin. ADP release precedes dissociation from actin and is rate-limiting in the cycle. (3) Myosin V walks in strides averaging ∼36 nm, the long pitch pseudo-repeat of the actin helix, each step coupled to a single ATP hydrolysis. Such a unitary displacement, the largest molecular step size measured to date, is required for a processive myosin motor to follow a linear trajectory along a helical actin track.
Collapse
Affiliation(s)
- A Mehta
- Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, 1230 York Avenue, New York, NY 10021-6399, USA.
| |
Collapse
|