Differential properties of native and tagged or untagged recombinant glucose isomerases of Streptomyces sp. SK and possible implication of the glycosylation

A comparative study was performed to investigate the biochemical properties of the native glucose isomerase produced by Streptomyces sp. SK (SKGI) and its two recombinant forms, the common recombinant (r-SKGI) and the tagged (His6-SKGI) isomerases. The findings revealed that the three glucose isomerases displayed different behaviors in particular in terms of thermoactivity, stability at high temperature and specific activity. The thermoactivity/thermostablity and specific activity of r-SKGI were lower than those of native SKGI. SDS-PAGE analyses revealed that native and r-SKGI showed different molecular weights. This could be attributed to the presence of 8% O-glycosylation in the SKGI monomers, which entailed a potential attachment of sugar residues having a total mass of about 3.44 kDa on Thr at positions 6 and/or 30. The results also demonstrated that the His-tagged SKGI was less thermoactive/thermostable than SKGI and r-SKGI. Electrophoretic analysis showed that the His tag significantly affected the dimerization of SKGI. A 3D model of His6-SKGI was constructed. The results showed that the Histidine attachment was located at the dimerization interface and that, unlike the rest of this interface, it was hydrophilic in nature, which presumably hamper the dimerization process and led to the decrease in thermoactivity/thermostablity and catalytic efficiency.