scholarly journals Mechanical model of muscle contraction 2. Kinematic and dynamic aspects of a myosin II head during the working stroke

2019 ◽  
Author(s):  
S. Louvet
Keyword(s):  
Actin Filament ◽  
Myosin Head ◽  
Myosin Ii ◽  
Tangential Force ◽  
Longitudinal Axis ◽  
Myosin Filament ◽  
Analytical Relationship ◽  
Shortening Velocity ◽  
Fixed Plane ◽  
Algorithmic Optimization

AbstractThe condition of a myosin II head during which force and movement are generated is commonly referred to as Working Stroke (WS). During the WS, the myosin head is mechanically modelled by 3 two by two articulated segments, the motor domain (S1a) strongly fixed to an actin molecule, the lever (S1b) on which a motor moment is exerted, and the rod (S2) pulling the myosin filament (Mfil). When the half-sarcomere (hs) is shortened or lengthened by a few nanometers, it is assumed that the lever of a myosin head in WS state moves in a fixed plane including the longitudinal axis of the actin filament (Afil). As a result, the 5 rigid segments, i.e. Afil, S1a, S1b, S2 and Mfil, follow deterministic and configurable trajectories. The orientation of S1b in the fixed plane is characterized by the angle θ. After deriving the geometric equations singularizing the WS state, we obtain an analytical relationship between the hs shortening velocity (u) and the angular velocity of the lever . The principles of classical mechanics applied to the 3 solids, S1a, S1b and S2, lead to a relationship between the motor moment exerted on the lever (MB) and the tangential force dragging the actin filament (TA). We distinguish θup and θdown, the two boundaries framing the angle θ during the WS, relating to up and down conformations. With the usual data assigned to the cross-bridge elements, a linearization procedure of the relationships between u and , on the one hand, and between MB and TA, on the other hand, is performed. This algorithmic optimization leads to theoretical values of θup and θdown equal to +28° (−28°) and −42° (+42°) respectively with a variability of ±5° in a hs on the right (left), data in accordance with the commonly accepted experimental values for vertebrate muscle fibers.

scholarly journals Mechanical model of muscle contraction. 6. Calculations of the tension exerted by a skeletal fiber during a shortening staircase

2019 ◽  
Author(s):  
Louvet S.
Keyword(s):  
Myosin Head ◽  
Myosin Ii ◽  
Velocity Curve ◽  
Shortening Velocity ◽  
Velocity Relationship ◽  
Length Step ◽  
Force Velocity ◽  
Uniform Law ◽  
Slope Line ◽  
Constant Slope

AbstractAccompanying Paper 1 tests a theoretical relationship between force and shortening velocity of a muscle fiber without justifying its validity. Paper 2 determines the kinematics and dynamics of a myosin II head during the working stroke (WS). Paper 3 imposes the Uniform law as a density representative of the orientation of the levers belonging to the WS heads. By support of these works, Papers 4 and 5 put into equation the evolution of the tension during the four phases of a length step. The present paper closes all six articles by imposing two tasks on itself. The first purpose is to apply the theoretical elements developed for a length step to a succession of identical length steps, otherwise known as shortening staircase. With the values of the geometric and temporal parameters assigned to a myosin head in Papers 1 to 5, a correct adjustment is established between the theoretical tension deduced from our model and the experimental tension published in 1997 by a team of Italian researchers relating to nine shortening staircases performed on the same fiber. In particular, we obtain the equation of the tension reached at the time end of the step (T*) which remains constant step by step as soon as the shortening of a half-sarcomere exceeds 17 nm. The second objective is to find and explain the equation of the Force-Velocity curve introduced ex abrupto into Paper 1: by decreasing the size and duration of the steps, the staircase tends towards a constant slope line corresponding to a continuous speed shortening. By applying the methods of infinitesimal calculus to the different formulations leading to T*, we deduce the Force-Velocity relationship (see Supplement S6.L). And the circle is complete.

scholarly journals Myosin II filament assemblies in the active lamella of fibroblasts: their morphogenesis and role in the formation of actin filament bundles.

1995 ◽  
Vol 131 (4) ◽  
pp. 989-1002 ◽  
Author(s):  
A B Verkhovsky ◽  
T M Svitkina ◽  
G G Borisy
Keyword(s):  
Electron Microscopy ◽  
Actin Filament ◽  
Mammalian Cells ◽  
Myosin Ii ◽  
Myosin Filament ◽  
Actin Bundles ◽  
Fluorescence And Electron Microscopy ◽  
Myosin Filaments ◽  
Filament Bundles ◽  
Filament Network

The morphogenesis of myosin II structures in active lamella undergoing net protrusion was analyzed by correlative fluorescence and electron microscopy. In rat embryo fibroblasts (REF 52) microinjected with tetramethylrhodamine-myosin II, nascent myosin spots formed close to the active edge during periods of retraction and then elongated into wavy ribbons of uniform width. The spots and ribbons initially behaved as distinct structural entities but subsequently aligned with each other in a sarcomeric-like pattern. Electron microscopy established that the spots and ribbons consisted of bipolar minifilaments associated with each other at their head-containing ends and arranged in a single row in an "open" zig-zag conformation or as a "closed" parallel stack. Ribbons also contacted each other in a nonsarcomeric, network-like arrangement as described previously (Verkhovsky and Borisy, 1993. J. Cell Biol. 123:637-652). Myosin ribbons were particularly pronounced in REF 52 cells, but small ribbons and networks were found also in a range of other mammalian cells. At the edge of the cell, individual spots and open ribbons were associated with relatively disordered actin filaments. Further from the edge, myosin filament alignment increased in parallel with the development of actin bundles. In actin bundles, the actin cross-linking protein, alpha-actinin, was excluded from sites of myosin localization but concentrated in paired sites flanking each myosin ribbon, suggesting that myosin filament association may initiate a pathway for the formation of actin filament bundles. We propose that zig-zag assemblies of myosin II filaments induce the formation of actin bundles by pulling on an actin filament network and that co-alignment of actin and myosin filaments proceeds via folding of myosin II filament assemblies in an accordion-like fashion.

scholarly journals Specification of Actin Filament Function and Molecular Composition by Tropomyosin Isoforms

2003 ◽  
Vol 14 (3) ◽  
pp. 1002-1016 ◽  
Author(s):  
Nicole S. Bryce ◽  
Galina Schevzov ◽  
Vicki Ferguson ◽  
Justin M. Percival ◽  
Jim J.-C. Lin ◽  
...  
Keyword(s):  
Cell Size ◽  
Functional Properties ◽  
Actin Filament ◽  
Actin Filaments ◽  
Myosin Ii ◽  
Molecular Composition ◽  
Cellular Migration ◽  
Stress Fibers ◽  
Human Homologue ◽  
Tropomyosin Isoforms

The specific functions of greater than 40 vertebrate nonmuscle tropomyosins (Tms) are poorly understood. In this article we have tested the ability of two Tm isoforms, TmBr3 and the human homologue of Tm5 (hTM5NM1), to regulate actin filament function. We found that these Tms can differentially alter actin filament organization, cell size, and shape. hTm5NM1was able to recruit myosin II into stress fibers, which resulted in decreased lamellipodia and cellular migration. In contrast, TmBr3 transfection induced lamellipodial formation, increased cellular migration, and reduced stress fibers. Based on coimmunoprecipitation and colocalization studies, TmBr3 appeared to be associated with actin-depolymerizing factor/cofilin (ADF)-bound actin filaments. Additionally, the Tms can specifically regulate the incorporation of other Tms into actin filaments, suggesting that selective dimerization may also be involved in the control of actin filament organization. We conclude that Tm isoforms can be used to specify the functional properties and molecular composition of actin filaments and that spatial segregation of isoforms may lead to localized specialization of actin filament function.

Mechanism of partial adaptation in airway smooth muscle after a step change in length

2007 ◽  
Vol 103 (2) ◽  
pp. 569-577 ◽  
Author(s):  
Farah Ali ◽  
Leslie Chin ◽  
Peter D. Paré ◽  
Chun Y. Seow
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Intermediate State ◽  
Ultrastructural Changes ◽  
Myosin Filament ◽  
Shortening Velocity ◽  
Myosin Filaments ◽  
Partial Adaptation ◽  
Static Conditions

The phenomenon of length adaptation in airway smooth muscle (ASM) is well documented; however, the underlying mechanism is less clear. Evidence to date suggests that the adaptation involves reassembly of contractile filaments, leading to reconfiguration of the actin filament lattice and polymerization or depolymerization of the myosin filaments within the lattice. The time courses for these events are unknown. To gain insights into the adaptation process, we examined ASM mechanical properties and ultrastructural changes during adaptation. Step changes in length were applied to isolated bundles of ASM cells; changes in force, shortening velocity, and myosin filament mass were then quantified. A greater decrease in force was found following an acute decrease in length, compared with that of an acute increase in length. A decrease in myosin filament mass was also found with an acute decrease in length. The shortening velocity measured immediately after the length change was the same as that measured after the muscle had fully adapted to the new length. These observations can be explained by a model in which partial adaptation of the muscle leads to an intermediate state in which reconfiguration of the myofilament lattice occurred rapidly, followed by a relatively slow process of polymerization of myosin filaments within the lattice. The partially adapted intermediate state is perhaps more physiologically relevant than the fully adapted state seen under static conditions, and it simulates a more realistic behavior for ASM in vivo.

scholarly journals A Single Myosin Head Moves along an Actin Filament with Regular Steps during One Biochemical Cycle of ATP Hydrolysis

2000 ◽  
Vol 40 (2) ◽  
pp. 89-93 ◽  
Author(s):  
Kazuo KITAMURA ◽  
Atsuko H. IWANE ◽  
Makio TOKUNAGA
Keyword(s):  
Actin Filament ◽  
Atp Hydrolysis ◽  
Myosin Head

Role of myosin II tail sequences in its function and localization at the cleavage furrow in Dictyostelium

1999 ◽  
Vol 112 (13) ◽  
pp. 2195-2201 ◽  
Author(s):  
S. Shu ◽  
R.J. Lee ◽  
J.M. LeBlanc-Straceski ◽  
T.Q. Uyeda
Keyword(s):  
Myosin Head ◽  
Myosin Ii ◽  
Equatorial Region ◽  
Chain Gene ◽  
Cleavage Furrow ◽  
Tail Domain ◽  
Specific Domain ◽  
Dictyostelium Myosin ◽  
Skeletal Myosin

Cytoplasmic myosin II accumulates in the cleavage furrow and provides the force for cytokinesis in animal and amoeboid cells. One model proposes that a specific domain in the myosin II tail is responsible for its localization, possibly by interacting with a factor concentrated in the equatorial region. To test this possibility, we have expressed myosins carrying mutations in the tail domain in a strain of Dictyostelium cells from which the endogenous myosin heavy chain gene has been deleted. The mutations used in this study include four internal tail deletions: Mydelta824-941, Mydelta943-1464, Mydelta943-1194 and Mydelta1156-1464. Contrary to the prediction of the hypothesis, immunofluorescence staining demonstrated that all mutant myosins were able to move toward the furrow region. Chimeric myosins, which consisted of a Dictyostelium myosin head and chicken skeletal myosin tail, also efficiently localized to the cleavage furrow. All these deletion and chimeric mutant myosins, except for Mydelta943-1464, the largest deletion mutant, were able to support cytokinesis in suspension. Our data suggest that there is no single specific domain in the tail of Dictyostelium myosin II that is required for its functioning at and localization to the cleavage furrow.

scholarly journals Molecular Architecture of Synaptic Actin Cytoskeleton in Hippocampal Neurons Reveals a Mechanism of Dendritic Spine Morphogenesis

2010 ◽  
Vol 21 (1) ◽  
pp. 165-176 ◽  
Author(s):  
Farida Korobova ◽  
Tatyana Svitkina
Keyword(s):  
Electron Microscopy ◽  
Actin Cytoskeleton ◽  
Actin Filament ◽  
Dendritic Spines ◽  
Dendritic Spine ◽  
Myosin Ii ◽  
Capping Protein ◽  
Dominant Feature ◽  
Presynaptic Boutons ◽  
Spine Morphogenesis

Excitatory synapses in the brain play key roles in learning and memory. The formation and functions of postsynaptic mushroom-shaped structures, dendritic spines, and possibly of presynaptic terminals, rely on actin cytoskeleton remodeling. However, the cytoskeletal architecture of synapses remains unknown hindering the understanding of synapse morphogenesis. Using platinum replica electron microscopy, we characterized the cytoskeletal organization and molecular composition of dendritic spines, their precursors, dendritic filopodia, and presynaptic boutons. A branched actin filament network containing Arp2/3 complex and capping protein was a dominant feature of spine heads and presynaptic boutons. Surprisingly, the spine necks and bases, as well as dendritic filopodia, also contained a network, rather than a bundle, of branched and linear actin filaments that was immunopositive for Arp2/3 complex, capping protein, and myosin II, but not fascin. Thus, a tight actin filament bundle is not necessary for structural support of elongated filopodia-like protrusions. Dynamically, dendritic filopodia emerged from densities in the dendritic shaft, which by electron microscopy contained branched actin network associated with dendritic microtubules. We propose that dendritic spine morphogenesis begins from an actin patch elongating into a dendritic filopodium, which tip subsequently expands via Arp2/3 complex-dependent nucleation and which length is modulated by myosin II-dependent contractility.

scholarly journals 3P162 Nucleotide turnover rates of bipolar myosin filament during actin filament sliding(11. Molecular motor,Poster)

2013 ◽  
Vol 53 (supplement1-2) ◽  
pp. S238
Author(s):  
Takahiro Maruta ◽  
Shingo Miyazaki ◽  
Takahiro Kobatake ◽  
Shigeru Chaen
Keyword(s):  
Actin Filament ◽  
Molecular Motor ◽  
Myosin Filament ◽  
Turnover Rates

scholarly journals Differential role of nonmuscle myosin II isoforms during blebbing of MCF-7 cells

2017 ◽  
Vol 28 (8) ◽  
pp. 1034-1042 ◽  
Author(s):  
Sumit K. Dey ◽  
Raman K. Singh ◽  
Shyamtanu Chattoraj ◽  
Shekhar Saha ◽  
Alakesh Das ◽  
...  
Keyword(s):  
Life Cycle ◽  
Actin Filament ◽  
Myosin Ii ◽  
Nonmuscle Myosin ◽  
Nonmuscle Myosin Ii ◽  
Different Types ◽  
Membrane Protrusions ◽  
Bleb Formation ◽  
Mcf 7

Bleb formation has been correlated with nonmuscle myosin II (NM-II) activity. Whether three isoforms of NM-II (NM-IIA, -IIB and -IIC) have the same or differential roles in bleb formation is not well understood. Here we report that ectopically expressed, GFP-tagged NM-II isoforms exhibit different types of membrane protrusions, such as multiple blebs, lamellipodia, combinations of both, or absence of any such protrusions in MCF-7 cells. Quantification suggests that 50% of NM-IIA-GFP–, 29% of NM-IIB-GFP–, and 19% of NM-IIC1-GFP–expressing MCF-7 cells show multiple bleb formation, compared with 36% of cells expressing GFP alone. Of interest, NM-IIB has an almost 50% lower rate of dissociation from actin filament than NM-IIA and –IIC1 as determined by FRET analysis both at cell and bleb cortices. We induced bleb formation by disruption of the cortex and found that all three NM-II-GFP isoforms can reappear and form filaments but to different degrees in the growing bleb. NM-IIB-GFP can form filaments in blebs in 41% of NM-IIB-GFP–expressing cells, whereas filaments form in only 12 and 3% of cells expressing NM-IIA-GFP and NM-IIC1-GFP, respectively. These studies suggest that NM-II isoforms have differential roles in the bleb life cycle.

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