Mutation of G138P Enhanced the Thermostability of D-glucose Isomerase.

In order to enhance the thermostability of D-glucose isomerase (GI), Gly 138 was decided to be the target to be replaced by molecular design. The mutant G138P was obtained by in vitro site-directed mutagenesis of GI gene. The recombinant plasmid pTKD-GI containing mutant site was expressed in E. coli K38 strain. The comparison experiments of GIG138P with wild-type GI showed that: (1) The half time of GIG138P was as about two times as that of the wild type. (2) The optimum temperature of GIG138P was increased by 10-12 degrees. (3) The specific-activity of GIG138P was similar to the wild-type GI. We supposed, based on the above facts, that the substitution of Pro for Gly at position 138 introduced a pyrrolidine ring, which could just fill perfectly the empty hole leaved by Gly-138 which has no side chain and could make the protein structure more rigid, therefore the mutant G138P enhanced the thermostability of SM33GI.