Figure 3.

2D Schematic Free Energy Landscape Illustrating the Effect of Interactions between the Nascent Polypeptide Chain (NC) and Ribosome on the Co-translational Folding Process.

Unfolded (U) and native (N) states are shown folding through a transition state (‡), and the free energy of folding, in the absence of additional interactions, is ΔG_free (indicated by dashed blue lines). However, interactions of unfolded and native states with the ribosome surface to form bound states (U_B and N_B, respectively) may perturb the effective free energy of folding of the ribosome–nascent chain complex (RNC), ΔG_RNC (indicated by dashed red lines). A stronger interaction with the ribosome of the unfolded state relative to the native state is illustrated here (depicted by the lower free energy of U_B compared with N_B), the effect of which is (i) that the folding equilibrium is shifted from the native state towards the unfolded state, and (ii) that the rates of folding (k_f) and unfolding (k_u) are both decreased due to the increased free energy barrier heights.