Nonlinear elasticity and an 8-nm working stroke of single myosin molecules in myofilaments.
Using optical trapping and fluorescence imaging techniques, we measured the step size and stiffness of single skeletal myosins interacting with actin filaments and arranged on myosin-rod cofilaments that approximate myosin mechanics during muscle contraction. Stiffness is dramatically lower for negatively compared to positively strained myosins, consistent with buckling of myosin's subfragment 2 rod domain. Low stiffness minimizes drag of negatively strained myosins during contraction at loaded conditions. Myosin's elastic portion is stretched during active force generation, reducing apparent step size with increasing load, even though the working stroke is approximately constant at about 8 nanometers. Taking account of the nonlinear nature of myosin elasticity is essential to relate myosin's internal structural changes to physiological force generation and filament sliding.
Kaya
Motoshi
M
Department of Physics, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyou-ku, Tokyo, 113-0033 Japan.
Higuchi
Hideo
H
D008841:Actin Cytoskeleton / Q000502:physiology*; D000205:Actomyosin / Q000737:chemistry / Q000502:physiology; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D003187:Compliance; D004548:Elasticity; D008954:Models, Biological; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000502:physiology; D018482:Muscle, Skeletal; D015879:Myosin Subfragments / Q000502:physiology; D009218:Myosins / Q000737:chemistry / Q000502:physiology*; D045663:Quantum Dots; D011817:Rabbits
D015879:Myosin Subfragments; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000205:Actomyosin; D009218:Myosins