Force-clamp experiments reveal the free-energy profile and diffusion coefficient of the collapse of protein molecules

H. Lannon, J. S. Haghpanah, J. K. Montclare, E. Vanden-Eijnden, J. Brujic

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We present force-clamp data on the collapse of ubiquitin polyproteins from a highly extended state to the folded length, in response to a quench in the force from 110 pN to 5 or 10 pN. Using a recent method for free-energy reconstruction from the observed nonequilibrium trajectories, we find that their statistics is captured by simple diffusion along the end-to-end length. The estimated diffusion coefficient of ∼100 nm2 s-1 is significantly slower than expected from viscous effects alone, possibly because of the internal degrees of freedom of the protein. The free-energy profiles give validity to a physical model in which the multiple protein domains collapse all at once and the role of the force is approximately captured by the Bell model.

Original languageEnglish (US)
Article number128301
JournalPhysical Review Letters
Issue number12
StatePublished - Mar 22 2013


ASJC Scopus subject areas

  • Physics and Astronomy(all)

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