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Updated: Dec 9, 2025

Probing Myosin Ensemble Mechanics in Actin Filament Bundles Using Optical Tweezers
Published on: May 4, 2022
Acto-Myosin Cross-Bridge Stiffness Depends on the Nucleotide State of Myosin II
Tianbang Wang1, Bernhard Brenner1, Arnab Nayak1
1Institute of Molecular and Cell Physiology, Hannover Medical School, 30625 Hannover, Germany.
Abstract:
How various myosin isoforms fulfill the diverse physiological requirements of distinct muscle types remain unclear. Myosin II isoforms expressed in skeletal muscles determine the mechanical performance of the specific muscles. Here, we employed a single-molecule optical trapping method and compared the chemomechanical properties of slow and fast muscle myosin II isoforms. Stiffness of the myosin motor is key to its force-generating ability during muscle contraction. We found that acto-myosin (AM) cross-bridge stiffness depends on its nucleotide state as the myosin progresses through the ATPase cycle. The strong actin bound "AM.ADP" state exhibited >2 fold lower stiffness than "AM rigor" state. The two myosin isoforms displayed similar "rigor" stiffness. We conclude that the time-averaged stiffness of the slow myosin is lower due to prolonged duration of the AM.ADP state, which determines the force-generating potential and contraction speed of the muscle, elucidating the basis for functional diversity among myosins.
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