Fig. 2. Salt bridges with P-degree greater than 20% in the concatenated equilibrium MD trajectories of the three proteases at the respective habitat temperatures of the source organisms. (A) Psychrophilic VPR at 283 K. (B) Mesophilic PRK at 300 K. (C) Thermophilic AQN at 343 K. The representative 3D structures are shown as backbone traces (yellow). The salt-bridging residues are shown as stick models, with the negatively and positively charged residues colored red and blue, respectively. Salt bridges are shown as green dashes. The boxed regions (i.e., I–IV) are those where salt bridges are relatively enriched (for details, see text in Discussion section).