Fig. 3.

Panel A. Thermophilic (NOX) and mesophilic (NTR) homologues of the nitroreductase fold, as studied by MD⁴³. The time evolution of the root mean square displacement (RMSD) with respect to the crystallographic configuration is reported in the left panels for the two proteins. The structure of the thermophilic protein remains close to the native structure even at high temperature (100°C) while the mesophilic counterpart initiates unfolding. The thermophile maintains its native contacts along the scanned temperatures while the mesophile starts losing its native contacts around 40°C. Data are extracted from figures 1 and 7 of Ref.⁴³. Panel B. Dielectric constant (ε_p) of three homologue proteins estimated using the Fröhlich-Kirkwood equation⁴⁶, $\frac{2{\epsilon }_s({\epsilon }_p-1)}{(2{\epsilon }_w+{\epsilon }_p)}=\frac{<\Delta M_p^2>}{k_{b}T{r}_p^3}$, with ε_s being the solvent dielectric constant, $\Delta M_p^2$ the fluctuation of the protein dipole moment and r_p the effective radius of the protein modeled as a spherical globule. Results show that for thermophiles the dielectric constant ε_p is larger than for mesophiles (see Fig. 3 in Ref.⁴⁶). Panel C. Low-frequency density of states, as computed in Ref.¹⁷ for a WT (black) and thermostable mutant (red). All data have been digitalized using the software PlotDigitizer and smoothed for the sake of clarity.