His-tag β-galactosidase supramolecular performance.

β-Galactosidase is an important biotechnological enzyme used in the dairy industry, pharmacology and in molecular biology. In our laboratory we have overexpressed a recombinant β-galactosidase in Escherichia coli (E. coli). This enzyme differs from its native version (β-Gal) in that 6 histidine residues have been added to the carboxyl terminus in the primary sequence (β-Gal), which allows its purification by immobilized metal affinity chromatography (IMAC). In this work we compared the functionality and structure of both proteins and evaluated their catalytic behavior on the kinetics of lactose hydrolysis. We observed a significant reduction in the enzymatic activity of β-Gal with respect to β-Gal. Although, both enzymes showed a similar catalytic profile as a function of temperature, β-Gal presented a higher resistance to the thermal inactivation compared to β-Gal. At room temperature, β-Gal showed a fluorescence spectrum compatible with a partially unstructured protein, however, it exhibited a lower tendency to the thermal-induced unfolding with respect to β-Gal. The distinctively supramolecular arranges of the proteins would explain the effect of the presence of His-tag on the enzymatic activity and thermal stability.