Enhancing the thermostability of glucose isomerase by protein engineering.

We have engineered recombinant glucose isomerase (GI) from Actinoplanes missouriensis by site-directed mutagenesis to enhance its thermal stability in both the soluble and immobilized forms. Substitution of arginine for lysine at position 253, which lies at the dimer/dimer interface of the GI tetramer, produced the largest stabilization under model industrial conditions. We discuss our results in terms of a model in which chemical glycation of lysines by sugars in the industrial corn syrup substrate represents a major pathway of destabilization.