UMMS Affiliation

Division of Cell Biology and Imaging, Department of Radiology; Craig Lab

Publication Date


Document Type



Amino Acids, Peptides, and Proteins | Cell Biology | Cellular and Molecular Physiology | Enzymes and Coenzymes


Super-relaxation is a state of muscle thick filaments in which ATP turnover by myosin is much slower than that of myosin II in solution. This inhibited state, in equilibrium with a faster (relaxed) state, is ubiquitous and thought to be fundamental to muscle function, acting as a mechanism for switching off energy-consuming myosin motors when they are not being used. The structural basis of super-relaxation is usually taken to be a motif formed by myosin in which the two heads interact with each other and with the proximal tail forming an interacting-heads motif, which switches the heads off. However, recent studies show that even isolated myosin heads can exhibit this slow rate. Here, we review the role of head interactions in creating the super-relaxed state and show how increased numbers of interactions in thick filaments underlie the high levels of super-relaxation found in intact muscle. We suggest how a third, even more inhibited, state of myosin (a hyper-relaxed state) seen in certain species results from additional interactions involving the heads. We speculate on the relationship between animal lifestyle and level of super-relaxation in different species and on the mechanism of formation of the super-relaxed state. We also review how super-relaxed thick filaments are activated and how the super-relaxed state is modulated in healthy and diseased muscles.


Contraction, Cell Motility

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© 2021 Craig and Padrón. This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 International license, as described at

DOI of Published Version



Craig R, Padrón R. Structural basis of the super- and hyper-relaxed states of myosin II. J Gen Physiol. 2022 Jan 3;154(1):e202113012. doi: 10.1085/jgp.202113012. Epub 2021 Dec 10. PMID: 34889960; PMCID: PMC8669498. Link to article on publisher's site

Journal/Book/Conference Title

The Journal of general physiology

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PubMed ID


Creative Commons License

Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.