Journal
PHYSICAL REVIEW E
Volume 78, Issue 6, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevE.78.061913
Keywords
biomechanics; entropy; free energy; hydrogen bonds; molecular biophysics; molecular configurations; proteins
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Funding
- Massachusetts Institute of Technology
- Army Research Office
- National Science Foundation
- Air Force Office of Scientific Research
- Office of Naval Research
- DARPA
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Elasticity and strength of individual beta-sheet protein domains govern key biological functions and the mechanical properties of biopolymers including spider silk, amyloids, and muscle fibers. The worm-like-chain (WLC) model is commonly used to describe the entropic elasticity of polypeptides and other biomolecules. However, force spectroscopy experiments have shown pronounced deviations from the ideal WLC behavior, leading to controversial views about the appropriate elastic description of proteins at nanoscale. Here we report a simple model that explains the physical mechanism that leads to the breakdown of the WLC idealization in experiments by using only two generic parameters of the protein domain, the H-bond energy and the protein backbone's persistence length. We show that a rupture initiation condition characterized by the free energy release rate of H-bonds characterizes the limit of WLC entropic elasticity of beta-sheet protein domains and the onset of rupture. Our findings reveal that strength and elasticity are coupled and cannot be treated separately. The predictions of the model are compared with atomic force microscopy experiments of protein rupture.
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