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Internal motions in myosin head: effect of ADP and ATP
1Central Research Laboratory, University Medical School, Pécs, Hungary.
Abstract:
Internal flexibility of myosin heads in glycerinated muscle fibres in the presence of MgADP plus orthovanadate and after addition of Ca-ATP was studied using an isothiocyanate-based spin label attached to the reactive sulfhydryl sites of myosin. The spin labels were immobilized on the microsecond time scale and exhibited significant orientational order in rigor. In AM+.ADP.V(i) state a smaller fraction of ordered population was found showing distinct orientation from rigor; the larger population of heads was in dynamically disordered state. This new ordered population of heads was detected even in contracting fibres.
Insights
Myosin head flexibility in muscle fibers was studied using spin labels. A disordered state was observed, with a distinct ordered population appearing during muscle contraction.
Area of Science:
- Muscle physiology
- Biophysics
- Molecular motor function
Background:
- Myosin heads undergo conformational changes during muscle contraction.
- Understanding myosin head flexibility is crucial for elucidating muscle mechanics.
Purpose of the Study:
- To investigate the internal flexibility of myosin heads in glycerinated muscle fibers.
- To characterize myosin head orientation and dynamics in different functional states.
Main Methods:
- Utilized an isothiocyanate-based spin label attached to myosin's reactive sulfhydryl sites.
- Studied spin label immobilization and orientational order on the microsecond timescale.
- Analyzed myosin head states including rigor, MgADP plus orthovanadate (AM+.ADP.V(i)), and Ca-ATP addition.
Main Results:
- Spin labels showed significant orientational order in the rigor state.
- In the AM+.ADP.V(i) state, a smaller ordered population with distinct orientation was observed, alongside a larger dynamically disordered population.
- A novel ordered population of myosin heads was detected even in actively contracting muscle fibers.
Conclusions:
- Myosin heads exhibit complex dynamics, transitioning between ordered and disordered states.
- The presence of a distinct ordered population during contraction suggests specific functional roles.
- These findings provide insights into the mechanical regulation of muscle contraction.