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Structural transition at actin's N-terminus in the actomyosin cross-bridge cycle
J E Hansen1, J Marner, D Pavlov
1Department of Chemistry and Biochemistry and Molecular Biology Institute, University of California, Los Angeles, California 90095, USA.
Biochemistry
|February 26, 2000
Summary
Investigating actomyosin dynamics, this study used a modified actin protein to show that the actin N-terminus interaction with myosin changes between weakly and strongly bound states. This finding offers new insights into muscle contraction mechanisms.
Area of Science:
- Biochemistry
- Molecular Biology
- Biophysics
Background:
- Actomyosin interactions are crucial for force and motion generation.
- These interactions cycle between weakly and strongly bound protein complexes.
- Actin's N-terminus is thought to be more involved in weak actomyosin binding.
Purpose of the Study:
- To investigate if actin's N-terminus interaction with myosin changes between weak and strong binding states.
- To understand the role of actin's N-terminus in actomyosin dynamics.
Main Methods:
- Constructed a yeast actin mutant (Cys-1) with N-terminal cysteine for labeling.
- Labeled the N-terminal cysteine with pyrene maleimide.
- Measured fluorescence changes upon myosin S1 binding to different actin-myosin states.
Main Results:
- Pyrenyl-Cys-1 actin showed properties similar to wild-type actin in polymerization and strong S1 binding.
- Weak S1 binding and in vitro motility showed minor alterations.
- Fluorescence increased upon S1 binding, with a ~75% greater increase in weakly bound states (MgATP, MgATPgammaS) compared to the strongly bound (rigor) state.
Conclusions:
- Demonstrated a transition at the actin N-terminus upon switching between weak and strong actomyosin binding states.
- Implies either altered proximity of the N-terminus to myosin or greater N-terminal conformational changes in weak binding states.