Stiffness, working stroke, and force of single-myosin molecules in skeletal muscle: elucidation of these mechanical prop
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Cellular and Molecular Life Sciences
Review
Stiffness, working stroke, and force of single‑myosin molecules in skeletal muscle: elucidation of these mechanical properties via nonlinear elasticity evaluation Motoshi Kaya · Hideo Higuchi
Received: 11 October 2012 / Revised: 27 February 2013 / Accepted: 25 April 2013 © Springer Basel 2013
Abstract In muscles, the arrays of skeletal myosin molecules interact with actin filaments and continuously generate force at various contraction speeds. Therefore, it is crucial for myosin molecules to generate force collectively and minimize the interference between individual myosin molecules. Knowledge of the elasticity of myosin molecules is crucial for understanding the molecular mechanisms of muscle contractions because elasticity directly affects the working and drag (resistance) force generation when myosin molecules are positively or negatively strained. The working stroke distance is also an important mechanical property necessary for elucidation of the thermodynamic efficiency of muscle contractions at the molecular level. In this review, we focus on these mechanical properties obtained from single-fiber and single-molecule studies and discuss recent findings associated with these mechanical properties. We also discuss the potential molecular mechanisms associated with reduction of the drag effect caused by negatively strained myosin molecules. Keywords Skeletal myosin · Stiffness · Working stroke size · Drag force · Nonlinear elasticity · Single molecule
Introduction Muscle contraction is driven by the cyclical interaction of myosin molecules with actin filaments and is associated with the hydrolysis of ATP molecules. The current view of
M. Kaya (*) · H. Higuchi Department of Physics, Graduate School of Science, The University of Tokyo, 7‑3‑1 Hongo Bunkyo‑ku, Tokyo 113‑0033, Japan e-mail: [email protected]‑tokyo.ac.jp
the muscle force generation mechanism is that myosin molecules bind to actin filaments along with the products of ATP hydrolysis (phosphate and/or ADP), which is followed by conformational changes (working stroke) of the myosin head to produce a sliding movement of actin filaments past myosin filaments [1, 2]. At this point, the distortion of the myosin head stores elastic energy that is a source of mechanical work for use against the external environment. Thus, this elastic distortion of the myosin molecule is characterized as stiffness (inverse of compliance) and has been modeled as an essential mechanical element for the force generation driven by cross-bridges during muscle contractions. In this model, the force was simply determined by multiplying the constant stiffness by the strain in each myosin molecule [3]. At the maximum shortening velocity with zero net force output, the myosin molecules must achieve mechanical equilibrium, in which the negatively strained myosin molecules generate the net drag (negative) forces that are equal in magnitude but in the opposite direction of the net working (positive) forces generated by the positive
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