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Internal friction of single polypeptide chains at high stretch
Bhavin S Khatri1, Katherine Byrne, Masaru Kawakami
1Department of Physics & Astronomy, University of Leeds, Leeds, UK. bhavin.khatri@physics.org
Faraday Discussions
|December 4, 2008
Summary
Single molecule experiments reveal internal friction in unfolded polypeptide chains. A new frictional worm-like chain model explains this friction, showing it increases with tension due to a rough bending energy landscape.
Area of Science:
- Biophysics
- Polymer Physics
Background:
- Atomic Force Microscopy (AFM) enables measurement of single-molecule viscoelasticity through Brownian fluctuations.
- Understanding internal molecular dynamics is crucial for comprehending conformational landscapes.
Purpose of the Study:
- To investigate the internal friction of unfolded polypeptide chains under high tension.
- To develop a theoretical model explaining the observed friction behavior.
Main Methods:
- Utilizing Atomic Force Microscopy (AFM) to measure Brownian fluctuations of single molecules.
- Developing and applying a frictional worm-like chain (FWLC) model based on Rayleigh dissipation function.
- Analyzing dissipation rate via Fourier components to derive an effective friction constant.
Main Results:
- Internal friction exhibits a power-law dependence on tension (exponent 1.3 +/- 0.5).
- Relaxation time was found to be largely independent of applied force.
- The FWLC model predicts a power-law increase in friction with tension (exponent 3/2), aligning with experimental data.
Conclusions:
- The observed high internal friction is significantly greater (approx. 7 orders of magnitude) than solvent friction alone.
- A rough underlying energy landscape for chain bending, particularly involving amino acids and peptide bonds, is proposed as the cause.
- This finding is consistent with recent studies on proteins and polysaccharides.
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