Changing the mechanical unfolding pathway of FnIII10 by tuning the pulling strength

TL;DR

This study uses all-atom Monte Carlo simulations to explore how different pulling conditions influence the unfolding pathways and intermediates of FnIII10, revealing the dependence of unfolding behavior on force and velocity.

Contribution

It demonstrates how varying pulling strength alters the unfolding pathways and intermediate states of FnIII10, providing insights into the mechanical unfolding process.

Findings

Unfolding pathways depend on pulling conditions.

Three major intermediates identified with distinct structural features.

Free-energy landscape shows multiple minima corresponding to states.

Abstract

We investigate the mechanical unfolding of the tenth type III domain from fibronectin, FnIII10, 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 the 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 the 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.