Supplementary Materials:
Figure s8- Time evolution of the REMD trajectories for the high pressure REMD
simulation. A) Fraction of the time that each replica (1-40) spends in the folded state
(rmsd <0.22 nm) over 1 ns time averages. All replicas were started from a folded
configuration. B) First folding time after unfolding to rmsd > 0.6 nm for replicas along
the trajectory (red line). The profile shows an exponential growth with exponent of the
order on 100 ns. C) Fraction of replicas that are folded at any time during the simulation
as a function of time (red line). All replicas, at different temperatures are averaged
together. The inset curve on c) is the time correlation function of the fraction folded timehistory. The correlation time for the fraction for replicas folded is ~50 ns. We use
simulation segments of twice this time, 100 ns, to estimate uncertainties in the averages
for the simulations at high pressure.
Figure S9. Contour maps of the free energy G(rmsd,Rg) (top panel), G(rmsd,d TrpHB)
(middle panel), G(rmsd,d Ion-pair ) (bottom panel), at 280K, 320K and 350K. The
contours show that the system occupies two main basins- -one corresponding to the
folded state and another to the unfolded state. However, the bottom contours show that
the ion-pair distance distribution for formed pairs (d Ion-pair < 0.6 nm) persists at
temperatures when the system is mostly unfolded (rmsd as large as 0.8 nm). For
comparison, the top panel reproduces the results in Figure 4.
Figure S10. Time histories of the rmsd vs. time for selected replica trajectories.
Transitions between the folded basins occur frequently. The blue dashed line marks the
rmsd < 0.15 nm substate. The green dashed line marks the 0.15 < rmsd < 0.22 substate.
The mean residence time in the rmsd < 0.15 nm basin is 0.10 ns. The mean residence
time in folded (rmsd < 0.4) basin is close to 100 ns. Given the minor structural
differences and the fast inter conversion between the two folded substates, we consider
the thermodynamics of the trp-cage to be two-state. However, the kinetics may not be
two-states.