Amino-acid interactions in psychrophiles, mesophiles, thermophiles, and hyperthermophiles: insights from the quasi-chemical approximation.

We investigate the mechanisms used by proteins to maintain thermostability throughout a wide range of temperatures. We use the quasi-chemical approximation to estimate interaction strengths for psychrophiles, mesophiles, thermophiles, and hyperthermophiles. Our results highlight the importance of core packing in thermophilic stability. Although we observed an increase in the number of charged residues, the contribution of salt bridges appears to be relatively modest by comparison. We observed results consistent with a gradual loosening of structure in psychrophiles, including a weakening of almost all types of interactions.