6SO3

The interacting head motif in insect flight muscle myosin thick filaments

Summary for 6SO3

• Entry DOI: 10.2210/pdb6so3/pdb
• EMDB information: 7029
• Descriptor: Myosin 2 heavy chain striated muscle, Myosin 2 essential light chain striated muscle, Myosin 2 regulatory light chain striated muscle (3 entities in total)
• Functional Keywords: myosin, thick filament, insect flight muscle, motor protein
• Biological source: Lethocerus indicus; More
• Total number of polymer chains: 6
• Total formula weight: 527929.33

Authors

Morris, E.P.,Knupp, C.,Squire, J.M. (deposition date: 2019-08-28, release date: 2020-07-08, Last modification date: 2024-05-15)

Primary citation

Knupp, C.,Morris, E.,Squire, J.M.
The Interacting Head Motif Structure Does Not Explain the X-Ray Diffraction Patterns in Relaxed Vertebrate (Bony Fish) Skeletal Muscle and Insect (Lethocerus) Flight Muscle.
Biology (Basel), 8:-, 2019

PubMed Abstract: Unlike electron microscopy, which can achieve very high resolution but to date can only be used to study static structures, time-resolved X-ray diffraction from contracting muscles can, in principle, be used to follow the molecular movements involved in force generation on a millisecond timescale, albeit at moderate resolution. However, previous X-ray diffraction studies of resting muscles have come up with structures for the head arrangements in resting myosin filaments that are different from the apparently ubiquitous interacting head motif (IHM) structures found by single particle analysis of electron micrographs of isolated myosin filaments from a variety of muscle types. This head organization is supposed to represent the super-relaxed state of the myosin filaments where adenosine triphosphate (ATP) usage is minimized. Here we have tested whether the interacting head motif structures will satisfactorily explain the observed low-angle X-ray diffraction patterns from resting vertebrate (bony fish) and invertebrate (insect flight) muscles. We find that the interacting head motif does not, in fact, explain what is observed. Previous X-ray models fit the observations much better. We conclude that the X-ray diffraction evidence has been well interpreted in the past and that there is more than one ordered myosin head state in resting muscle. There is, therefore, no reason to question some of the previous X-ray diffraction results on myosin filaments; time-resolved X-ray diffraction should be a reliable way to follow crossbridge action in active muscle and may be one of the few ways to visualise the molecular changes in myosin heads on a millisecond timescale as force is actually produced.

PubMed: 31540109
DOI: 10.3390/biology8030067

Experimental method

ELECTRON MICROSCOPY (6.2 Å)