Myosin and actin filaments are highly organized within muscle sarcomeres. Myosin-binding protein C (MyBP-C) is a flexible, rod-like protein located within the C-zone of the sarcomere. The C-terminal domain of MyBP-C is tethered to the myosin filament backbone, and the N-terminal domains are postulated to interact with actin and/or the myosin head to modulate filament sliding. To define where the N-terminal domains of MyBP-C are localized in the sarcomere of active and relaxed mouse myocardium, the relative positions of the N terminus of MyBP-C and actin were imaged in fixed muscle samples using super-resolution fluorescence microscopy. The resolution of the imaging was enhanced by particle averaging. The images demonstrate that the position of the N terminus of MyBP-C is biased toward the actin filaments in both active and relaxed muscle preparations. Comparison of the experimental images with images generated in silico, accounting for known binding partner interactions, suggests that the N-terminal domains of MyBP-C may bind to actin and possibly the myosin head but only when the myosin head is in the proximity of an actin filament. These physiologically relevant images help define the molecular mechanism by which the N-terminal domains of MyBP-C may search for, and capture, molecular binding partners to tune cardiac contractility.
The N terminus of myosin-binding protein C extends toward actin filaments in intact cardiac muscle
J.W. McNamara’s present address is Murdoch Children’s Research Institute, The Royal Children’s Hospital, Parkville, Victoria, Australia.
K.H. Lee’s present address is Massachusetts Facility for High-Resolution Electron Cryo-microscopy, University of Massachusetts Medical School, Worcester, MA.
This work is part of a special collection on myofilament function and disease.
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Sheema Rahmanseresht, Kyoung H. Lee, Thomas S. O’Leary, James W. McNamara, Sakthivel Sadayappan, Jeffrey Robbins, David M. Warshaw, Roger Craig, Michael J. Previs; The N terminus of myosin-binding protein C extends toward actin filaments in intact cardiac muscle. J Gen Physiol 1 March 2021; 153 (3): e202012726. doi: https://doi.org/10.1085/jgp.202012726
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