High level of soluble expression and purification of catalytically active native UDP-galactose 4-epimerase of Aeromonas hydrophila in E. coli

The ubiquitous Aeromonas hydrophila is responsible for several pathological conditions in fish and human. Like most gram negative bacteria, its virulence relies on outer membrane lipopolysachharide (LPS). The Leloir pathway enzyme UDP-galactose 4-epimerase (GalE), plays an important role in the LPS biosynthesis, and therefore is a potential drug target. We have earlier carried out extensive biochemical and biophysical studies with histidine-tagged recombinant GalE. However, for effective drug design it is desirable to understand the structure-function relation of a protein in its native form without any additional sequences or tags. In the present study, we report the high level expression, purification and characterization of recombinant GalE (rGalE) of Aeromonas hydrophila in its native form in E coli. The rGalE expressed as a soluble protein was purified to near homogeneity. From 1 L of shake flask culture ~15 mg of purified rGalE was obtained. The purified protein was biologically active with Km and Kcat values of 0.7 mM and 28.8 s, respectively. The enzyme exhibited a temperature and pH optima of 37 ̊C and 7 9, respectively. Thus, the present study employed for soluble expression and purification of functionally active rGalE without any tag bypasses the need for cumbersome strategies associated with removal of tag from purified protein.