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Structure and structural change of the myosin head
M Tokunaga1, K Sutoh, T Wakabayashi
1College of Arts and Sciences, University of Tokyo, Japan.
Advances in Biophysics
|January 1, 1991
Summary
Researchers located the myosin ATPase site using 3D electron microscopy. Myosin head shape changes, particularly bending, are linked to muscle contraction mechanisms and influenced by ADP-Vi.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- Myosin heads possess critical functional sites, including the actin-binding and ATPase sites.
- Understanding the spatial arrangement and conformational changes of these sites is crucial for elucidating muscle contraction.
Purpose of the Study:
- To precisely locate the ATPase site on the myosin head using advanced electron microscopy techniques.
- To investigate the domain structure and conformational dynamics of myosin heads, specifically the bending mechanism.
- To correlate myosin head shape changes with functional states, such as the presence of ADP-Vi.
Main Methods:
- Three-dimensional electron microscopy combined with the avidin-biotin system to pinpoint the ATPase site.
- Utilizing monoclonal and site-directed antibodies to map other functional sites on the myosin head.
- Rotary-shadowing and uni-directional shadowing electron microscopy techniques to examine myosin head morphology and bending.
- Analysis of myosin head conformation under varying conditions, including the presence of ADP-Vi.
Main Results:
- The ATPase site was localized approximately 5 nm from the myosin head tip and 4 nm from the actin-binding site.
- Two distinct myosin head shapes were observed: straight and bent, with bending occurring at 12 ± 2 nm from the head-rod junction.
- The bending region was identified at the domain boundary, and the presence of ADP-Vi was found to shift the equilibrium towards the bent conformation.
- The location and angle of bending remained consistent across examined conditions.
Conclusions:
- The precise localization of functional sites provides insights into the domain structure of the myosin head.
- Myosin head conformation exists in an equilibrium between straight and bent states, influenced by nucleotide binding (ADP-Vi).
- The observed bending mechanism of the myosin head is proposed to be a significant factor in the molecular processes of muscle contraction.