Expression and purification of inclusion body of Serratia marcescens nuclease relying on SUMO fusion

Abstract Serratia marcescens nuclease (SM nuclease) can remove nucleic acid residues in recombinant protein drugs and reduce the viscosity of bacteria, exhibiting great significance in investigating these drugs. However, its underexpression in E. coli leads to less protein amount obtained by purification of inclusion body and low enzyme activity. In this study, the Small Ubiquitin-like Modifier (SUMO) tag was fused to the N-terminus of the SM nuclease and cloned into the pET28a vector. Subsequently, the expression and purification of inclusion body of the SUMO-fused SM nuclease were compared with those of SM nuclease without SUMO fusion. The results revealed that SUMO fusion elevated the expression of inclusion body of the SM nuclease, but exerted no effect on soluble expression of the protein. Meanwhile, SUMO fusion increased the solubility of inclusion body proteins and enhanced the removal of surface impurities during inclusion body washing. On the other hand, SUMO fusion promoted correct folding of the protein and improved the efficiency of refolding. The High-Performance Liquid Chromatography (HPLC) results indicated a protein concentration of 99% after two cycles of affinity chromatography for SUMO-fused SM nuclease. Additionally, the activity of the SUMO-fused protein (4×106 U/mg) was 32 times higher than that of the unfused protein. SUMO fusion yielded approximately 10 mg of SM nuclease protein with a purity of 99% from 1 g of bacteria.