Cloning and Characterization of a Sucrose Isomerase from Erwinia rhapontici NX-5 for Isomaltulose Hyperproduction

Abstract

The sucrose isomerase (SIase) gene from an efficient strain of Erwinia rhapontici NX-5 for isomaltulose hyperproduction was cloned and overexpressed in Escherichia coli. Protein sequence alignment revealed that SIase was a member of the glycoside hydrolase 13 family. The molecular mass of the purified recombinant protein was estimated at 66kDa by SDS-PAGE. The SIase had an optimal pH and temperature of 5.0 and 30°C, respectively, with a K (m) of 257mmol/l and V (max) of 48.09μmol/l/s for sucrose. To the best of our knowledge, the recombinant SIase has the most acidic optimum pH for isomaltulose synthesis. When the recombinant E. coli (pET22b- palI) cells were used for isomaltulose synthesis, almost complete conversion of sucrose (550g/l solution) to isomaltulose was achieved in 1.5h with high isomaltulose yields (87%). The immobilized E. coli cells remained stable for more than 30days in a "batch"-type enzyme reactor. This indicated that the recombinant SIase could continuously and efficiently produce isomaltulose.