UMMS Affiliation

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

Publication Date


Document Type



Biochemistry | Biophysics | Cell Biology | Cellular and Molecular Physiology | Molecular Biology


Myosin molecules in the relaxed thick filaments of striated muscle have a helical arrangement in which the heads of each molecule interact with each other, forming the interacting-heads motif (IHM). In relaxed mammalian skeletal muscle, this helical ordering occurs only at temperatures > 20 degrees C and is disrupted when temperature is decreased. Recent x-ray diffraction studies of live tarantula skeletal muscle have suggested that the two myosin heads of the IHM (blocked heads [BHs] and free heads [FHs]) have very different roles and dynamics during contraction. Here, we explore temperature-induced changes in the BHs and FHs in relaxed tarantula skeletal muscle. We find a change with decreasing temperature that is similar to that in mammals, while increasing temperature induces a different behavior in the heads. At 22.5 degrees C, the BHs and FHs containing ADP.Pi are fully helically organized, but they become progressively disordered as temperature is lowered or raised. Our interpretation suggests that at low temperature, while the BHs remain ordered the FHs become disordered due to transition of the heads to a straight conformation containing Mg.ATP. Above 27.5 degrees C, the nucleotide remains as ADP.Pi, but while BHs remain ordered, half of the FHs become progressively disordered, released semipermanently at a midway distance to the thin filaments while the remaining FHs are docked as swaying heads. We propose a thermosensing mechanism for tarantula skeletal muscle to explain these changes. Our results suggest that tarantula skeletal muscle thick filaments, in addition to having a superrelaxation-based ATP energy-saving mechanism in the range of 8.5-40 degrees C, also exhibit energy saving at lower temperatures ( < 22.5 degrees C), similar to the proposed refractory state in mammals.


Biochemistry, Biophysics, Contraction and Cell Motility, Myofilament

Rights and Permissions

© 2021 Ma et al. 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



Ma W, Duno-Miranda S, Irving T, Craig R, Padrón R. Relaxed tarantula skeletal muscle has two ATP energy-saving mechanisms. J Gen Physiol. 2021 Mar 1;153(3):e202012780. doi: 10.1085/jgp.202012780. PMID: 33480967; PMCID: PMC7822627. Link to article on publisher's site

Journal/Book/Conference Title

The Journal of general physiology

Related Resources

Link to Article in PubMed

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.