Mechanical unfolding of proteins L and G with constant force: similarities and differences.

Mechanical unfolding of proteins L and G, which have similar structures, is considered in this work, and the question arises what changes happen in the unfolding pathways under the action of mechanical force. Molecular dynamics simulations with explicit water (134 trajectories) demonstrate that the mechanical unfolding with constant force occurs through at least two pathways in both proteins. These pathways practically coincide for both proteins and under different constant extensional forces (600, 700, 800, 900, and 1050 pN) and at different temperatures (320, 350, and 400 K at F=1050 pN). Go-like modeling of forced unfolding of proteins L and G does not agree with experimental results that protein G is more mechanically resistant than protein L. At the same time, molecular dynamics simulations of forced unfolding of proteins L and G with explicit water demonstrate that protein G is more mechanically resistant than protein L. Our investigation demonstrates that mechanical stable elements are the same for both proteins, namely, the N-terminal beta-hairpin. This result agrees with experimental data on denaturant unfolding for protein L but not for protein G.