Fig. 7.

Salt dependence of the thermodynamics of VPK unfolding. The equilibrium populations of the folded and unfolded conformations of VPK, described in terms of a four-state parallel pathway model under different monovalent salt conditions, are plotted as a function of temperature, as obtained from either coarse-grained simulations (A–E) or fits to the VPK-pC fluorescence melting profiles (F–J). Populations are shown for the fully folded VPK (pink), partially folded hairpins pkHP1 and pkHP2 (green and orange, respectively), and fully unfolded U (blue). Four sets of populations are shown: two from fits to the VPK-pC melting profiles (thick lines) and two from fits to the derivatives (thin lines), with either the $\text{PK}\iff \text{pkHP}1$ or the $\text{PK}\iff \text{pkHP}2$ transition temperature constrained from the simulation results (continuous and dashed lines, respectively).