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Myosin catalytic domain flexibility in MgADP
1Institute of Molecular Biophysics, Florida State University, Tallahassee 32306-3015.
Biochemistry
|November 29, 1994
Summary
The myosin head undergoes significant internal reorganization when ADP is added to rigor muscle fibers. This domain flexibility suggests multiple internal configurations and dynamic motions within the myosin head.
Area of Science:
- Biophysics
- Muscle Physiology
- Protein Dynamics
Background:
- Muscle contraction involves complex conformational changes in the myosin motor domain.
- Understanding myosin head dynamics is crucial for elucidating the mechanics of muscle contraction and ATP hydrolysis.
Purpose of the Study:
- To investigate internal domain reorganization and dynamics of the myosin head upon ADP binding to rigor muscle fibers.
- To differentiate between global domain rotation and localized internal motions.
Main Methods:
- Conventional Electron Paramagnetic Resonance (EPR) studies using a novel alpha-iodoketo spin label at Cys-707 of the myosin head.
- Saturation-transfer EPR to measure microsecond motions.
- Comparison with EPR data from maleimide and iodoacetamide spin labels.
Main Results:
- Addition of ADP to rigor fibers induced substantial internal domain reorganization, with probes becoming disordered.
- The labeled domain exhibited large-amplitude microsecond motions (tau r = 150 microseconds) in the presence of ADP.
- These internal motions contrasted with the absence of global motion reported by other spin labels, indicating localized flexibility.
Conclusions:
- The myosin head, even in a single chemical state (AM.ADP), can adopt multiple internal configurations, some of which are dynamic.
- Slow structural fluctuations within the myosin head may be linked to the slow release of actomyosin ATPase hydrolysis products.