Improving human skeletal muscle myosin heavy chain fiber typing efficiency

Murach, Kevin A.; Bagley, James R.; McLeland, Kathryn A.; Arevalo, José A.; Ciccone, Anthony B.; Malyszek, Kylie K.; Wen, Yuan; Galpin, Andrew J.

doi:10.1007/s10974-016-9441-9

Cited by 19 publications

(20 citation statements)

References 45 publications

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“…Simulation is based on dispersion of thick filament structure surmised from the atomic model of Alamo et al [27] as described in METHODS. In vivo relaxed skeletal (sk) myosin step-size from zebrafish embryo trunk muscle (red) is shown for comparison [31]. …”

Section: Resultsmentioning

confidence: 99%

Auxotonic to isometric contraction transitioning in a beating heart causes myosin step-size to down shift

et al. 2017

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Myosin motors in cardiac ventriculum convert ATP free energy to the work of moving blood volume under pressure. The actin bound motor cyclically rotates its lever-arm/light-chain complex linking motor generated torque to the myosin filament backbone and translating actin against resisting force. Previous research showed that the unloaded in vitro motor is described with high precision by single molecule mechanical characteristics including unitary step-sizes of approximately 3, 5, and 8 nm and their relative step-frequencies of approximately 13, 50, and 37%. The 3 and 8 nm unitary step-sizes are dependent on myosin essential light chain (ELC) N-terminus actin binding. Step-size and step-frequency quantitation specifies in vitro motor function including duty-ratio, power, and strain sensitivity metrics. In vivo, motors integrated into the muscle sarcomere form the more complex and hierarchically functioning muscle machine. The goal of the research reported here is to measure single myosin step-size and step-frequency in vivo to assess how tissue integration impacts motor function.A photoactivatable GFP tags the ventriculum myosin lever-arm/light-chain complex in the beating heart of a live zebrafish embryo. Detected single GFP emission reports time-resolved myosin lever-arm orientation interpreted as step-size and step-frequency providing single myosin mechanical characteristics over the active cycle. Following step-frequency of cardiac ventriculum myosin transitioning from low to high force in relaxed to auxotonic to isometric contraction phases indicates that the imposition of resisting force during contraction causes the motor to down-shift to the 3 nm step-size accounting for >80% of all the steps in the near-isometric phase. At peak force, the ATP initiated actomyosin dissociation is the predominant strain inhibited transition in the native myosin contraction cycle. The proposed model for motor down-shifting and strain sensing involves ELC N-terminus actin binding.Overall, the approach is a unique bottom-up single molecule mechanical characterization of a hierarchically functional native muscle myosin.

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Section: Resultsmentioning

confidence: 99%

Auxotonic to isometric contraction transitioning in a beating heart causes myosin step-size to down shift

et al. 2017

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“…Hence, the power output from titin Ig folding is highly cooperative. Furthermore, it is misleading to say that actomyosin contraction is synchronous while titin folding is not (111). It is generally accepted that myosin driven muscle shortening occurs by “cyclic asynchronous ATP-driven actin-myosin contractions” (112).…”

Section: Synchronization Of Titin Folding With Actomyosin Contractionmentioning

confidence: 99%

The Work of Titin Protein Folding as a Major Driver in Muscle Contraction

Eckels

Tapia‐Rojo

Rivas‐Pardo

et al. 2018

Annu. Rev. Physiol.

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Single molecule atomic force microscopy and magnetic tweezers experiments have demonstrated that titin Ig domains are capable of folding against a pulling force, generating mechanical work which exceeds that produced by a myosin motor. We hypothesize that upon muscle activation, formation of actomyosin crossbridges reduces the force on titin causing entropic recoil of the titin polymer and triggering the folding of the titin Ig domains. In the physiological force range of 4–15 pN under which titin operates in muscle, the folding contraction of a single Ig domain can generate 200% of the work of entropic recoil, and occurs at forces which exceed the maximum stalling force of single myosin motors. Thus titin operates like a mechanical battery storing elastic energy efficiently by unfolding Ig domains, and delivering the charge back by folding when the motors are activated during a contraction. We advance the hypothesis that titin folding and myosin activation act as inextricable partners during muscle contraction.

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“…HG also greatly exaggerated MHC IIx, particularly in individuals with >4% MHC IIa/IIx. The inability of HG to account for MHC IIa/IIx explains why MHC IIx appear common in some studies (48) even though their actual abundance in healthy human skeletal muscle is extraordinarily rare; typically <0.1% (9, 22–25, 27) and 0 of the >2,100 isolated fibers from the current sample. Thus, the seeming conversion of MHC IIx to IIa with exercise is more precisely IIa/IIx changing to IIa.…”

Section: Discussionmentioning

confidence: 91%

“…Thus, SF indicates how frequently each isoform exists but cannot address how much area each FT occupies within the muscle. HG addresses the latter, but cannot delineate hybrids, therefore inaccurately quantifying FT% (9, 21-25, 27).…”

Section: Methodsmentioning

confidence: 99%

Extraordinary Fast-Twitch Fiber Abundance in Elite Weightlifters

Serrano

Colenso-Semple

Lazauskas

et al. 2018

Preprint

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2 29 ABSTRACT 30 Human skeletal muscle fibers exist across a continuum of slow → fast-twitch. The amount of each 31 fiber type (FT) influences muscle performance but remains largely unexplored in elite athletes, 32 particularly from strength/power sports. To address this nescience, vastus lateralis (VL) biopsies 33 were performed on World/Olympic (female, n=6, "WCF") and National-caliber (female, n=9, 34 "NCF"; and male, n=6, "NCM") American weightlifters. Participant accolades included 3 35 Olympic Games, 19 World Championships, 25 National records, and >170 National/International 36 medals. Samples were analyzed for myosin heavy chain (MHC) content via SDS-PAGE using two 37 distinct techniques: single fiber (SF) distribution (%) and homogenate (HG) composition. These 38 athletes displayed the highest MHC IIa concentrations ever reported in healthy VL (23±9% I, 5±3% 39 I/IIa, 67±13% IIa, and 6±10% IIa/IIx), with WCF expressing a notable 71±17% (NCF=67±8%, 40 NCM=63±16%). The heavyweights accounted for 91% of the MHC IIa/IIx fibers. When compared 41 to SF, HG overestimated MHC I (23±9 vs. 31±9%) and IIx (0±0 vs. 3±6%) by misclassifying I/IIa 42 fibers as I and IIa/IIx fibers as IIx. These findings suggest athlete caliber (World vs. National), 43 training experience, and body mass determine FT% more than sex and refutes the common 44 pronouncement that women possess more slow and fewer fast-twitch fibers than men. Our results 45 also show the abundance of pure MHC IIa and rarity of IIx in elite strength/power-trained athletes, 46 indicate a potential link between MHC IIa/IIx frequency and body mass, and question the fidelity 47 of HG as a measure of FT% distribution. The extreme fast-twitch abundance partially explains 48 how elite weightlifters generate high forces in rapid time-frames. These data highlight the need for 49 more cellular and molecular muscle research on elite anaerobic athletes.

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Improving human skeletal muscle myosin heavy chain fiber typing efficiency

Cited by 19 publications

References 45 publications

Auxotonic to isometric contraction transitioning in a beating heart causes myosin step-size to down shift

Auxotonic to isometric contraction transitioning in a beating heart causes myosin step-size to down shift

The Work of Titin Protein Folding as a Major Driver in Muscle Contraction

Extraordinary Fast-Twitch Fiber Abundance in Elite Weightlifters

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