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Myosin-ATP chemomechanics
1Department of Biochemistry, School of Dentistry, University of the Pacific, San Francisco, California 94115.
Biochemistry
|March 16, 1993
Summary
Myosin subfragment 1 (S1) undergoes structural changes upon MgATP binding and hydrolysis, reducing its hydrodynamic size. This conformational change likely powers muscle filament sliding during ATP hydrolysis.
Area of Science:
- Biophysics
- Muscle Physiology
- Molecular Motor Function
Background:
- Myosin subfragment 1 (S1) is a key motor protein in muscle contraction.
- Understanding the structural dynamics of S1 during ATP hydrolysis is crucial for elucidating muscle function.
Purpose of the Study:
- To investigate the hydrodynamic size changes of rabbit skeletal muscle myosin S1 during the ATP hydrolysis cycle.
- To determine if these structural changes can explain the mechanical work performed by myosin.
Main Methods:
- Transient electrical birefringence techniques were used to measure the rotational decay time (tau) of S1.
- A hydrodynamic model of a four-bead structure was employed to interpret the birefringence data.
- Conformational changes were analyzed by fitting the model to experimental decay times.
Main Results:
- The hydrodynamic size of S1 decreased upon formation of the S1-MgADP,Pi intermediate.
- Rotational decay times indicated a significant structural rearrangement, with a bend angle change from 20 to 38 degrees.
- This structural change corresponds to a displacement of at least 3.9 nm at one end of S1.
Conclusions:
- MgATP binding and hydrolysis induce substantial structural rearrangements in myosin S1.
- The observed displacement during ATP hydrolysis is sufficient to account for the filament sliding observed in muscle and in vitro motility assays.
- This study provides a mechanistic link between myosin's structural dynamics and its force-generating capabilities.