Transport proteins PotD and Crr of Escherichia coli, novel fusion partners for heterologous protein expression

The Escherichia coli proteome response to the stressor GdnHCl was analyzed through 2-dimensional gel electrophoresis (2-DE). We identified PotD (spermidine/putrescine-binding periplasmic protein) and Crr [glucose-specific phosphotransferase (PTS) enzyme IIA component] as a stress-responsive protein. Even under a stress situation where the total number of soluble proteins decreased by about 10%, 3.5- and 2.2-fold increase was observed in the synthesis of PotD and Crr, respectively. As fusion partners, PotD and Crr dramatically increased the solubility of many aggregation-prone heterologous proteins [e.g. human minipro-insulin (mp-INS), human epidermal growth factor (EGF), human prepro-ghrelin (ppGRN), human interleukin-2(hIL-2), human activation induced cytidine deaminase (AID), human glutamate decarboxylase (GAD_448-585), Pseudomonas putida cutinase (CUT), human ferritin light chain (hFTN-L), human granulocyte colony-stimulating factor (G-CSF), and cold autoinflammatory syndrome1 protein (NALP3) Nacht domain (NACHT)] in the E. coli cytoplasm. Presumably PotD and Crr were very effective in shielding interactive surfaces of heterologous proteins associated with non-specific protein-protein interactions leading to the formation of inclusion bodies most likely due to intrinsic high folding efficiency, chaperone-like activity, or a combination of both factors. Both the stress-induced proteins were well suited for the production of a biologically active fusion mutant of P. putida cutinase that can be expected to be of biotechnological and commercial interest.