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Coiled-coil response to mechanical force: global stability and local cracking.
1Department of Mechanical Engineering, University of Texas, Austin, TX, USA.
Biophysical Journal
|August 27, 2013
Summary
Coiled coils, crucial protein structures, resist mechanical cracking at lower loads by rapid refolding. Higher loads cause unfolding, particularly near charged residue E929.
Area of Science:
- Protein structure and mechanics
- Biophysics
- Computational biology
Background:
- Coiled coils are vital protein structural motifs.
- They are composed of α-helices and are found in motor and structural proteins.
- These proteins are known to transmit mechanical loads.
Purpose of the Study:
- To analyze coiled-coil cracking under load using atomically detailed simulations.
- To quantify the kinetics and thermodynamics of coiled-coil mechanical failure.
- To investigate the role of specific residues and interactions in mechanical stability.
Main Methods:
- Atomically detailed simulations of a β-myosin S2 coiled-coil segment.
- Application of constant-magnitude tensile forces (0-200 pN).
- Utilized Milestoning to capture cracking kinetics and thermodynamics.
Main Results:
- Low loads (<100 pN) induced rapid refolding after initial cracking, without helix unfolding propagation.
- High loads (200 pN) led to regular unfolding propagation along and between helices.
- Unfolding events were concentrated near the charged residue E929.
- Hydrophobic interactions and interhelix hydrogen bonds showed minimal load-dependent variation.
Conclusions:
- Coiled coils exhibit load-dependent mechanical responses, with refolding dominating at lower stress.
- The charged residue E929 plays a critical role in initiating and localizing unfolding events.
- Milestoning analysis provides quantitative insights into the timescale of coiled-coil mechanical failure.
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