Temperature effects on structure and dynamics of the psychrophilic protease subtilisin S41 and its thermostable mutants in solution.

The psychrophilic protease subtilisin S41 from the Antarctic bacillus TA41, and two variants with two and seven amino acid substitutions were studied using molecular dynamics simulation at 283 and 363 K. The analysis of protein dynamics revealed that the average global flexibility of both variants was slightly higher than wild type at both 283 and 363 K. Essential dynamics analysis evidenced that the most relevant collective motions, especially at 363 K, differ in distribution and intensity for each protein variant. At high temperature and for the thermo labile wild type, an amplification of a subset of the low-temperature largest collective motions was observed. On the other hand, the two thermostable variants showed a rather different pattern of essential motions at 363 K from those at 283 K. These results support the hypothesis that the introduced amino acid substitutions, rather than improving the global stability of the variants by increasing its rigidity, lead to a change on the principal fluxional modes allowing the protein to explore a different subset of conformations. A better understanding of this process can open alternative strategies to increase the enzyme stability in addition to increasing the rigidity of the protein scaffold.