Heterologous protein expression using a novel stress-responsive protein of E. coli RpoA as fusion expression partner

E. coli proteome response to the stressor 2-HEDS was analyzed through two-dimensional gel electrophoresis (2-DE), and we identified DNA-directed RNA polymerase α-subunit (RpoA) as stress-responsive protein. Even under stress situation where the total number of soluble proteins decreased by 9.8%, the synthesis level of RpoA was increased 1.5-fold. As a fusion expression partner as well as solubility enhancer, RpoA facilitated the folding and increased significantly the solubility of many aggregation-prone heterologous proteins (human minipro-insulin, human epidermal growth factor, human prepro-ghrelin, human interleukin-2, human activation induced cytidine deaminase, human glutamate decarboxylase, Pseudomonas putida cutinase, human ferritin light chain, human granulocyte colony-stimulating factor, and cold inflammatory syndrome1 protein Nacht domain) in E. coli cytoplasm. Due probably to intrinsic high folding efficiency and/or chaperone-like activity, RpoA was very effective in shielding interactive surfaces of heterologous proteins that are associated with non-specific protein-protein interaction leading to the formation of inclusion bodies. RpoA was also well suited for the production of biologically active fusion mutant of Pseudomonas putida cutinase that is of much biotechnological and commercial interest.