Cysteine Engineering of an Endo-polygalacturonase from JCM 12802 to Improve Its Thermostability.

Thermostable enzymes have many advantages for industrial applications. Therefore, in this study, computer-aided design technology was used to improve the thermostability of a highly active endo-polygalacturonase from JCM12802 at an optimal temperature of 70 °C. The melting temperature and specific activity of the obtained mutant T316C/G344C were increased by 10 °C and 36.5%, respectively, compared with the wild-type enzyme. The crystal structure of the T316C/G344C mutant showed no formation of a disulfide bond between the introduced cysteines, indicating a different mechanism than the conventional mechanism underlying improved enzyme thermostability. The cysteine substitutions directly formed a new alkyl hydrophobic interaction and caused conformational changes in the side chains of the adjacent residues Asn315 and Thr343, which in turn caused a local reconstruction of hydrogen bonds. This method greatly improved the thermostability of the enzyme without affecting its activity; thus, our findings are of great significance for both theoretical research and practical applications.