Cultivation to improve in vivo solubility of overexpressed arginine deiminases in Escherichia coli and the enzyme characteristics

BACKGROUND Overexpression of foreign genes in Escherichia coli cells is an efficient means to obtain recombinant proteins. The technique is, however, often hampered by misfolding, degradation, aggregation and formation in inclusion bodies of products. RESULTS In this study, we reported that in vivo solubility of overexpressed arginine deiminases (ADI) improved by changing the cultivation conditions. ADI is enzymes that convert L-arginine to L-citrulline. After codon optimization, we synthesized the ADI gene of Pseudomonas putida and constructed it for overexpression in E. coli cells. The rADI products were mainly in inclusion body forms. We performed a series of optimization to enhance solubility of the protein. Co-expression with the GroES-GroEL chaperone team increased approximately 5-fold of the rADI activity. In addition the combination of L-arginine and D-glucose in the Luria-Bertani (LB) growth medium further increased the total activity to about 15 times. Separate L-arginine and D-glucose or the addition of other saccharides or amino acids had no such effects. The solubilization effects of the combination of L-arginine and D-glucose were further confirmed in the overexpression of another ADI from Listeria welshimeri. The enzymatic and conversion characteristics of the rADI products were further determined. CONCLUSIONS Combined addition of L-arginine and D-glucose in the LB medium significantly improved in vivo solubility of rADI proteins. The present study suggested a new strategy to increase the solubilization of overexpressed recombinant proteins in E. coli cells.