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Electron microscopy of the actin-myosin head complex in the presence of ATP
1Department of Cell Biology, University of Massachusetts Medical School, Worcester 01655.
Abstract:
The structure of the actin-myosin head complex during the ATPase cycle has been studied by electron microscopy of negatively stained acto-heavy-meromyosin. In the absence of ATP, heavy meromyosin molecules generally showed a regular, angled appearance, with both heads attached to the actin filament. In the presence of ATP, attached molecules showed a less ordered structure, often with only one head attached. We conclude that configurations other than the rigor structure occur during the actomyosin cross-bridge cycle.
Insights
The actin-myosin structure changes during muscle contraction. Electron microscopy reveals that ATP binding alters the myosin head attachment to actin filaments, indicating dynamic configurations beyond the rigor state.
Area of Science:
- Muscle physiology
- Biochemistry
- Structural biology
Background:
- The actin-myosin interaction is fundamental to muscle contraction.
- Understanding the structural dynamics of the actomyosin complex is crucial for elucidating muscle function.
- The ATPase cycle drives the conformational changes in myosin heads.
Purpose of the Study:
- To investigate the structural changes of the actin-myosin head complex during the ATPase cycle.
- To visualize the molecular configurations of acto-heavy-meromyosin under different nucleotide conditions.
Main Methods:
- Electron microscopy of negatively stained acto-heavy-meromyosin.
- Observation of molecular structures in the absence and presence of Adenosine Triphosphate (ATP).
Main Results:
- In the absence of ATP, heavy meromyosin molecules exhibited a regular, angled structure with both heads bound to actin.
- In the presence of ATP, attached molecules displayed a less ordered structure, frequently with only one myosin head attached to actin.
- These findings suggest dynamic structural rearrangements occur during the actomyosin cross-bridge cycle.
Conclusions:
- The actin-myosin complex adopts various structural configurations beyond the rigor state during its functional cycle.
- ATP binding significantly influences the attachment and conformation of myosin heads on actin filaments.
- These dynamic structural changes are essential for muscle contraction and force generation.