Changing the Mechanical Unfolding Pathway of FnIII(10) by Tuning the Pulling Strength

Simon Mitternacht, Stefano Luccioli, Alessandro Torcini, Alberto Imparato, Anders Irbäck

    Research output: Contribution to journalArticlepeer-review


    We investigate the mechanical unfolding of the tenth type III domain from fibronectin (FnIII(10)) both at constant force and at constant pulling velocity, by all-atom Monte Carlo simulations. We observe both apparent two-state unfolding and several unfolding pathways involving one of three major, mutually exclusive intermediate states. All three major intermediates lack two of seven native beta-strands, and share a quite similar extension. The unfolding behavior is found to depend strongly on the pulling conditions. In particular, we observe large variations in the relative frequencies of occurrence for the intermediates. At low constant force or low constant velocity, all three major intermediates occur with a significant frequency. At high constant force or high constant velocity, one of them, with the N- and C-terminal beta-strands detached, dominates over the other two. Using the extended Jarzynski equality, we also estimate the equilibrium free-energy landscape, calculated as a function of chain extension. The application of a constant pulling force leads to a free-energy profile with three major local minima. Two of these correspond to the native and fully unfolded states, respectively, whereas the third one can be associated with the major unfolding intermediates.
    Original languageEnglish
    Pages (from-to)429-441
    JournalBiophysical Journal
    Issue number2
    Publication statusPublished - 2009

    Subject classification (UKÄ)

    • Biophysics


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