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III - Contraction musculaire

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Importance de la contraction musculaire

• Forme de mouvement la mieux connue• Volontaire : vertébrés

– Courir, marcher, nager, voler =– Contraction de muscles squelettiques sur des os

• Involontaire– Cœur– Péristaltisme intestinal– Contraction de muscles cardiaque et lisse

• Même mécanisme moléculaire de base– Glissement de filaments d’actine sur des filaments de

myosine II grâce à l’ATP

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Phylogenèse

• Apparu tardivement

44

Cellule musculaire

• Longue, fine fibre musculaire

• Résulte de la fusion de myoblastes

• Nombreux noyaux sous la membrane plasmique

• Cytoplasme rempli de myofibrilles

55

Fig 16-68

A. Fibre musculaire squelettique

– Diamètre 50 m– Longueur jusqu'à plusieurs

centimètres– Myofibrilles

B. Fibre musculaire squelettique

– Fluorescence– Noyaux en bleu

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Myofibrilles

• Cylindrique

• Diamètre : 1 – 2 m• Longueur celle de la fibre

• Suite d’unités : le sarcomère (2,2 m) • Muscle strié (striation transversale)

99

Fig 16-69(A)

12 Myofibrilles (lapin) (détail dia suivante)– Striation transversale

2 2 mm2 2 mm

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Fig 16-69(BC)

• Deux myofibrilles adjacentes

• Définition du sarcomère

• Sarcomère• Bandes sombres (A)

et claires (I)• Disques Z (points

d’attache des extrémités + des filaments d’actine)

• Ligne M(ittle)

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Disques A (anisotrope) / I (isotrope)

• Disque A– Filaments épais– Anisotropes en lumière polarisée : l’indice de

réfraction change en fonction du plan de polarisation

• Disque I– Filaments fins– Isotrope car densité inférieure

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Strie Z

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Muscle Contractile Assemblies John

M. Squire, Hind A. Al‐khayat, Carlo

Knupp, and Pradeep K. Luther

• Fig. 11. The structure of α actinin and the two vertebrate Z band lattices. (A) The ubiquitous protein α actinin is an anti parallel homodimer. Each 100 KDa monomer comprises four central spectrin repeats (S1 to S4) an EF hand domain and two calponin homology domains (CH) at the N terminus. The EF hand domains bind calcium in non muscle cells. One α actinin molecule binds two actin filaments via the calponin homology domains. α Actinin binds titin via EF hand domains. (B, C) The Z band is the site where actin filaments from adjacent sarcomeres overlap in a tetragonal lattice and are crosslinked by α actinin molecules. The polarity and origin of the actin filaments is indicated by U (up) and D (down). The appearance of the Z band in cross section is typically basketweave like (B) or small square like (C). The appearance is reported to transform between the two appearances depending on the state of the muscle.

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R, Woodhead JL.

• Fig 1 Myosin molecules and thick filaments. (a) Striated muscle sarcomere showing overlapping arrays of thick and thin filaments. Thick filaments are connected at the M-line and thin filaments at the Z-line. The sarcomere shortens (bringing about contraction of muscle as a whole) by sliding of the thin filament arrays towards each other, increasing their overlap with thick filaments. (b) Central portion of the thick filament model showing the helical array (red dashed line) of pairs of myosin heads on the filament surface (each pair is represented by a yellow sphere). The green backbone contains myosin tails. The model represents a filament with fourfold rotational symmetry. The axial distance between adjacent levels of heads is 14.5 nm and, in this model, the helical repeat (43.5 nm) is three times the 14.5 nm spacing. (c) Schematic representation of the assembly of myosin molecules in a bipolar thick filament. The head ends of the molecules point away from the filament center in each half. Tails have antiparallel and parallel overlaps in the central bare zone (free of heads), but only parallel overlaps in the distal portions of the filament. (d) Myosin molecule. The tail (S2 and LMM) is a coiledcoil formed from the C-terminal halves of each heavy chain (red and green). Heads (S1) comprise the motor domain (MD) and light chain domain (LCD), which contains the essential light chain (ELC, blue) and regulatory light chain (RLC, yellow).

Myosin molecules and thick filaments

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Curr Opin Struct Biol. 2006,16(2):204-12. Structure and function of myosin filaments. Craig R, Woodhead JL.

• Figure 2. Head organization in striated muscle filaments. (a) Negatively stained thick filament from tarantula muscle (protein white). Helical tracks of heads are apparent by viewing along the filament axis at a glancing angle. (b) Helical 3D reconstruction of tarantula thick filament (5 nm resolution) based on negative-stain images. Data set from surface rendered using UCSF Chimera . (c) Single-particle 3D reconstruction of tarantula thick filament (2.5 nm resolution) based on cryo-EM images . The axial distance between adjacent levels of heads is 14.5 nm and the helical repeat is 43.5 nm. The ‘tilted-J’ (blue dots) represents a pair of myosin heads. The larger diameter of this reconstruction compared with (b), which is at the same scale, is due to shrinkage with negative staining (the heads also appear to partially collapse onto the backbone, resulting in loss of information and lower resolution in negative stain). (d) Reconstruction in (c) fitted with the atomic model of smooth muscle myosin (PDB code 1i84) at two 14.5 nm levels . In both the atomic model (based on crystallographic studies) and the filament, one head of each pair (green) has its actin-binding site blocked by binding to the converter region (located in the motor domain) and essential light chain of the other (red). Interactions also occur between heads from different levels. S2, whose position was uncertain in the atomic model, has been modeled as an α-helical coiled-coil (the α-helices have the same colors as the corresponding heads from which they arise), filling a rod of density in the reconstruction that runs from the head–head junction down towards the filament backbone. S2 appears to interact with blocked heads from both its own and the next 14.5 nm level. These multiple interactions could prevent the heads from hydrolyzing ATP and interacting with actin, thus switching the filament off.

Organisation des têtes dans les filaments du muscle strié

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• Figure 3. Backbone structure of striated muscle thick filaments (transverse views, shown for a filament with fourfold rotational symmetry). (a) Molecular crystal model. Each circle represents one myosin tail). (b) Subfilament model. Each subfilament is 4 nm in diameter and contains three myosin tails.. (c) Projected density of a 43.5 nm repeat of tarantula thick filament reconstruction (protein white). Twelve subunits, 4 nm in diameter and of high density (red circles), representing the thick filament backbone, run parallel to the filament axis — as predicted by the subfilament model for a filament with the tarantula symmetry. Note that (c) is shown at a smaller scale than (a,b); lower density material at higher radius represents heads.

Structure des filaments épais du muscle strié

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• Figure 4. Non-myosin proteins in vertebrate striated muscle thick filaments. Schematic diagram of a sarcomere (thin filaments omitted) showing a thick filament (green backbone, myosin heads omitted) and myosin-associated proteins. Titin molecules (blue) run from the M-line (where they overlap with molecules from the opposite half of the sarcomere), along the thick filament, then through the I-band (the zone between the thick filament and the Z-line), where they have an elastic domain, and ending at the Z-line, where they would overlap with titin from the next sarcomere. Myosin-binding proteins (MyBP, yellow), primarily MyBP-C, occupy 11 sites 43 nm apart in the proximal portions of each half thick filament.

Protéines des filaments épais du muscle strié des vertébrés en

dehors de la myosine

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Curr Opin Struct Biol. 2006,16(2):204-12. Structure and function of myosin filaments. Craig R, Woodhead JL.

• Figure 5. Schematic diagram of a side-polar thick filament. In the side-polar mode of assembly, found in smooth muscle thick filaments, antiparallel tail interactions occur along the entire length of the filament (c.f. bipolar filaments), so that opposite sides, rather than opposite ends, of the filament have opposite polarity. Functionally, the filament is still bipolar and able to pull actin filaments in opposite directions from opposite ends. The double arrows indicate how bipolar myosin dimers could easily associate with and dissociate from the filament ends, consistent with assembly-disassembly processes thought to occur in some smooth muscles in different physiological states.

Schéma d’un filament épais à polarité latérale (muscle lisse)

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Curr Opin Struct Biol. 2006,16(2):204-12. Structure and function of myosin filaments. Craig R, Woodhead JL.

• Figure 6. Myosin tail domains involved in thick filament assembly. Schematic representation of the myosin tail sequence showing the locations of various regions thought to be involved in the correct assembly of thick filaments (composite diagram based on different myosins; not all sites are involved in all myosins). These include a negative charge cluster, N1 (red), and two positive charge clusters, P1 (blue) and P2 (purple); an assembly competence domain or ACD (yellow) [55 and 58••]; the non-helical tailpiece or NHT (green); and four skip residues (dark blue). Smooth muscle and non-muscle myosins lack the indicated skip residue.

Domaines de queues de myosine impliqués dans l’assemblage des

filaments épais

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• Fig. 12. Z band modular structures. The axial width of the Z band varies with fiber type: fast muscles typically have narrow Z bands of width 4070 nm, and slow and cardiac muscles have wide Z bands of width 100 nm. (A–D) Electron micrographs of longitudinal sections of the Z band in (A) fish body white muscle (Luther, 1991); (B) fish fin muscle (Luther, 2000); (D) frog sartorius muscle (Luther et al., 2003); and (D) bovine neck (slow) muscle (Luther et al., 2002). The left and right panels show the primary orthogonal lattice views obtained by tilting the sections by 90° in the electron microscope. (E–H) The corresponding schematic views of the electron micrographs in A–D. Luther et al. (2003) proposed that these modular patterns are determined by the number of α actinin layers within the width of the Z band. (I) Stereo view of a model of a 6 α actinin layer Z band as found in slow muscle (Luther et al., 2003). Pairs of α actinin layers occur close together in longitudinal projection and give rise to three zigzag layers observed in electron micrographs, as shown by the model image superimposed on a corresponding electron micrograph (J).

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Filament fin

• Actine et protéines associées

• Extrémité plus fixées dans la strie Z

• Extrémité moins « cappée » au milieu du sarcomère

• Chevauche les filaments épais

• Organisation hexagonale avec un filament d’actine entre deux filaments

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Fig 16-70

• Coupe transversale de muscle en microscopie électronique (insecte : les filaments épais sont creux)

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khayat, Carlo Knupp, and Pradeep

K. Luther

• Fig. 3. (A) Actin filament composed of actin molecules (A), two tropomyosin stands (TM), and troponin molecule complexes (TN). (B) Myosin filament composed of myosin molecules shown in (C) with the rod of the myosin molecules forming the backbone of the filament and the myosin heads are arranged on the surface of the filament backbone. (D) The bipolar packing of the myosin molecules showing the anti parallel arrangement giving rise to a heads free bare zone region at the centre of the filament. This is also illustrated in (E). (F) Sarcomere structure extending between two successive Z bands (M, myosin, A, actin). (G–J) Cross sectional views through different parts of the sarcomere, showing (G) the square lattice of actin filaments in the I band; (H) the hexagonal lattice between overlapping arrays of actin and myosin filaments in the A band; (I, J) the hexagonal lattice of myosin filaments in the M band (I) and bare zone (J) regions, with the extra M protein density linking the myosin filaments at the M region in the center of the sarcomere (I).

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• Fig. 10. (A–F) A band filament lattices in different striated muscles showing the threefold myosin filaments in vertebrates, the fourfold myosin filaments in some invertebrates, and the sevenfold myosin filaments in scallop striated adductor muscle. The ratio of actin to myosin filaments within the different lattices is also shown. Two smooth muscle types are also illustrated; the face polar or side polar myosin filaments in vertebrate smooth muscle (G) and the large paramyosin containing filaments in molluskan smooth muscles (H).

ADVANCES IN PROTEIN

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Assemblies John M. Squire, Hind

A. Al‐khayat, Carlo Knupp,

and Pradeep K. Luther

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Muscle lisse et cœur

• Présence de sarcomères

• Mais organisation moins régulière

3131

Fig 16-71

• Modèle du glissement de la contraction musculaire

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Fig 16-72

• Organisation des protéines accessoires dans un sarcomère

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Molecular Architecture In Muscle Contractile Assemblies John M. Squire, Hind A. Al‐khayat, Carlo Knupp, and Pradeep K. Luther

• Fig. 14. Stereo pairs of the transverse structure (A) and the axial structure (B) of a 3D model relating successive half sarcomeres in vertebrate striated muscles. In both images, the wide blue and brown cylinders represent actin filaments, the gray cross links schematically represent α actinin bridges between anti parallel actin filaments, the narrow green and purple cylinders represent titin strands in one half sarcomere, and the narrow dark blue and red cylinders represent titin strands in the other half sarcomere. The narrow green and red cylinders represent single titin strands, whereas the narrow purple and dark blue cylinders represent paired titin strands. The myosin filaments are shown as brown cylinders. At the bottom of the structure (more obvious in B), there are seven myosin filaments, one central and six surrounding this, and at the top of the structure, for clarity, there is just a single myosin filament. Since the actin/α actinin Z band assembly appears to be a strong structure and is an early development in myogenesis, one can alternatively look on the 3D model as showing that there are balanced lateral forces keeping the myosin filament tips in the A band in the correct lateral positions relative to the actin filaments emanating from the Z band. At the same time the titin strands are held relatively clear of the actin filaments throughout most of the I band, thus allowing them to behave freely as parallel elastic elements. The opposite tilting of the titin and actin filament displacements in a given I band and the generally balanced 3D distribution of forces on the Z band actin filaments make this a very attractive model. (Modified from Knupp et al., 2002.)

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• Fig. 5. (A) Electron micrograph picture showing a whole sarcomere from fish muscle in relaxing conditions (Z to Z distance about 2.3 μm). (B) Schematic diagram showing the sarcomere with titin molecules (green and blue) with the N terminus of each titin molecule located at the Z band and the C terminus at the M band. (C) Arrangement of the C protein within the A band showing seven stripes on each half of the myosin filament. (D) Magnified version of the area between the Z band and I band showing the PEVK and N2 domains of titin and the end filament at the tip of the myosin filament.

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Luther

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Au,Y2004p3016

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Rôle du calcium dans la contraction musculaire

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Fig 16-73(A)

Tubules T et reticulum sarcoplasmique

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Fig 16-73(B)

Tubules T et reticulum sarcoplasmique

3939

Fig 16-73(C)

Tubules T et reticulum sarcoplasmique

4040

Fig 16-74

Contrôle de la contraction musculaire par la troponine

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Muscle cardiaque

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Fig 16-75

• Conséquences d'une petite mutation du gène de la myosine sur le cœur

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Knupp, and Pradeep K. Luther

• Fig. 1. (A) Schematic illustration of the hierarchy of muscle. Skeletal muscle is composed of fibers about 20 to 100 μm in diameter and very long. Fibers in the light microscope appear cross striated and the muscles they come from are known as striated muscles. Striations are from repeating units, the sarcomeres, with A band and I band regions. Each sarcomere extends between successive Z bands and is about 2.2 to 2.3 μm long in a resting muscle (Bloom and Fawcett, 1975). (B) Groups of muscle fibers (F), showing they are multinucleated (N), and composed of the myofibrils (MF). Myofibrils may be about 2 to 5 μm in diameter. (C) Representation of the muscle cell arrangement in animal hearts, showing similar striations to those seen in skeletal muscles, but here the cells (the myocytes) are much shorter, they contain a single nucleus (N), and they are linked end to end by special structures known as intercalated disks (D), which provide mechanical and electrical continuity between cells. (D) A typical smooth muscle that can be found surrounding the blood vessels and various hollow organs apart from the heart. These visceral muscles do not have cross striations. M, mitochondria, Z, Z band, N, Nucleus.

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• Fig. 30. Comparison of the X ray–modeled myosin head arrays in relaxed fish muscle (A) and relaxed insect flight muscle (B), with the motor (catalytic) domain of outer myosin heads in each model circled to show the close similarity of their configurations in the two different species. The M band is at the bottom in both models