Significance Cardiovascular disease continues to be the leading cause of death worldwide, and is frequently associated with heart failure. Efforts develop better therapeutics for failure have been held back by limited understanding normal control contraction on timescale heartbeat. We used synchrotron X-ray diffraction determine dynamic structural changes in myosin motors that drive muscle, show filament-based mechanisms time course strength contraction, allowing those targeted developing...

Abstract Recent X-ray diffraction studies on actively contracting fibres from skeletal muscle showed that the number of myosin motors available to interact with actin-containing thin filaments is controlled by stress in myosin-containing thick filaments. Those results suggested filament mechano-sensing might constitute a novel regulatory mechanism striated muscles acts independently well-known filament-mediated calcium signalling pathway. Here we test hypothesis using probes attached light...

Contraction of skeletal muscle is triggered by a transient rise in intracellular calcium concentration leading to structural change the actin-containing thin filaments that allows binding myosin motors from thick filaments. Most are unavailable for actin resting because they folded back against filament backbone. Release stress, implying positive feedback loop However, it was unclear how and activation mechanisms coordinated, partly most previous studies regulation were conducted at low...

Muscle contraction is driven by myosin motors from the thick filaments pulling on actin-containing thin of sarcomere, and it regulated structural changes in both filaments. Thin are activated an increase intracellular calcium concentration [Ca 2+ ] i binding to actin. Thick direct sensing filament load. However, these mechanisms cannot explain muscle relaxation when decreases at high load attached There is, therefore, a fundamental gap our understanding relaxation, despite its importance for...

A shortening muscle is a machine that converts metabolic energy into mechanical work, but, when stretched, it acts as brake, generating high resistive force at low cost. The braking action of can be activated with remarkable speed, the leg extensor muscles rapidly decelerate body end jump. Here we used time-resolved x-ray and measurements on isolated cells to elucidate molecular basis its rapid control. We show stretch only 5 nm between each overlapping set myosin actin filaments in...

Myosin motors in the thick filament of resting striated (skeletal and cardiac) muscle are trapped an OFF state, which packed helical tracks on surface, inhibiting their interactions with actin utilization ATP. To investigate structural changes induced mammalian skeletal by temperature, we collected x-ray diffraction patterns from fast extensor digitorum longus mouse temperature range near physiological (35°C) to 10°C, maximal isometric force (T0) shows a threefold decrease. In muscle,...

Muscle contraction is driven by a change in the structure of head domain myosin, “working stroke” that pulls actin filaments toward midpoint myosin filaments. This movement heads can be measured very precisely intact muscle cells X-ray interference, but until now this technique has not been applied to physiological activation and force generation following electrical stimulation cells. By using approach, we show long axes domains are roughly parallel resting muscle, with their center mass...

Key points Contraction of skeletal muscle is thought to be regulated by a structural change in the actin‐containing thin filaments sarcomere, but recent results have suggested that myosin‐containing thick may also involved. We show filament structure resting depends on overlap with region containing myosin binding protein C (MyBP‐C). During isometric contraction, regions do not are highly disordered, contrast their helical order muscle. The provide strong support for role transition...

Force generation in the muscle sarcomere is driven by head domain of myosin molecule extending from thick filament to form cross-bridges with actin-containing thin filament. Following attachment, a structural working stroke pulls towards centre sarcomere, producing, under unloaded conditions, sliding ∼ 11 nm. The mechanism force depends on relationship between cross-bridge and movement, which determined compliances (C(cb)) filaments. By measuring dependence spacing high-order myosin-...

Significance The efficiency of the heart as a pump depends on an autoregulatory mechanism, Frank–Starling law heart, that potentiates strength contraction in response to increase ventricular filling. Disruption this mechanism compromises ability blood, potentially leading failure. We used fluorescent probes myosin muscle cells investigate molecular basis mechanism. Our results show stronger at longer lengths is due calcium-dependent interfilament signaling pathway links stress sensing...

The role of the actin filament-associated protein nebulin on mechanical and kinetic properties actomyosin motor was investigated in skeletal muscle wild-type (wt) nebulin-deficient (nebulin(-)(/)(-)) mice that were 1 d old, an age at which sarcomeric structure is still well preserved. In Ca2+-activated skinned fibers from psoas muscle, we determined Ca2+ dependence isometric force stiffness, rate redevelopment after unloaded shortening (k(TR)), power during isotonic shortening, velocity...

Myosin filament mechanosensing determines the efficiency of contraction by adapting number switched ON motors to load. Accordingly, unloaded shortening velocity (V0 ) is already set at end latency relaxation (LR), ∼10 ms after start stimulation, when myosin still in OFF state. Here actin-attached per half-myosin (n) during V0 imposed either LR or plateau isometric estimated from relation between half-sarcomere compliance and force redevelopment shortening. The value n decreases progressively...

Contraction of skeletal muscle is regulated by structural changes in both actin-containing thin filaments and myosin-containing thick filaments, but myosin-based regulation unlikely to be preserved after filament isolation, its basis remains poorly characterized. Here, we describe the periodic features structure situ high-resolution small-angle x-ray diffraction interference. We used relaxed demembranated fibers resting intact preparations assess whether fibers, which have been widely for...

Time-resolved X-ray diffraction of isolated fast-twitch muscles mice was used to show how structural changes in the myosin-containing thick filaments contribute regulation muscle contraction, extending previous focus on by actin-containing thin filaments. This study shows that activation involves following sequence changes: filament activation, disruption helical array myosin motors characteristic resting muscle, release motor domains from folded conformation backbone, and actin attachment....

Structural and mechanical changes occurring in the myosin filament head domains during development of isometric tetanus have been investigated intact frog muscle fibres at 4 degrees C 2.15 microm sarcomere length, using level mechanics X-ray diffraction beamline ID2 European Synchrotron Radiation Facility (Grenoble, France). The time courses both M3 M6 myosin-based reflections were recorded with 5 ms frames gas-filled RAPID detector (MicroGap Technology). Following end latent period (11...

Significance Muscle contraction is controlled by structural changes in the thin filament of muscle sarcomere triggered calcium binding to troponin. It has long been suspected that myosin an additional effect switching on filament, but biological function this was unknown. We have elucidated situ sequence calcium-induced troponin and identified a kinetic component tracking filament. propose model regulation with kinetics determined coordinated structures both thick filaments response...

Rapid attachment to actin of the detached motor domain myosin dimers with one already attached has been hypothesized explain stretch-induced changes in X-ray interference and stiffness active muscle. Here, using half-sarcomere mechanics single frog muscle fibres (2.15 μm sarcomere length 4°C), we show that: (1) an increase under stretch is specific isometric contraction does not occur rigor, indicating that mechanism number motors; (2) 2 ms after 100 μs stretches (amplitude 2–8 nm per...

Key points The force in the half‐sarcomere (hs), functional unit of muscle, is due to contributions individual myosin motors arranged parallel half‐myosin filament and pulling on opposing actin filament. According a linear hs model, during an isometric contraction rises its maximal steady value ( T 0 ) proportion number actin‐attached motors, while strain with slope that depends compliance myofilaments. We measured stiffness, superimposing small 4 kHz length oscillations development...

X-ray diffraction patterns were recorded from isolated single fibres of frog skeletal muscle during isometric contraction at temperatures between 0 and 17 degrees C. Isometric force was 43 +/- 2% (mean S.E.M., n = 10) higher C than The intensity the first actin layer line increased by 57 18% (n 5), ratio intensities equatorial 1,1 1,0 reflections 20 7% 10), signalling radial or azimuthal motions myosin head domains. M3 reflection axial repeat heads along filaments 27 4% more intense C,...

Structural changes in myosin motors and filaments during relaxation from short tetanic contractions of intact single fibres frog tibialis anterior muscles at sarcomere length 2.14 mum, 4 degrees C were investigated by X-ray diffraction. Force declined a steady rate for several hundred milliseconds after the last stimulus, while lengths remained almost constant. During this isometric phase intensities equatorial meridional M3 reflections associated with radial axial distributions also...

Myosin filament-based regulation supplements actin to control the strength and speed of contraction in heart muscle. In diastole, myosin motors form a folded helical array that inhibits interaction; during contraction, they are released from array. A similar structural transition has been observed mammalian skeletal muscle, which cooling below physiological temperature shown reproduce some features activation filaments active contraction. Here, we used small-angle x-ray diffraction...