Comparative production of human interleukin-2 fused with green fluorescent protein in several recombinant expression systems

The selection of an optimal recombinant expression system is important for successful protein production. Here, we compared production of human interleukin-2 (hIL-2)-green fluorescent protein (GFP) fusion proteins in several expression systems such as bacteria Escherichia coli, yeast Pichia pastoris, insect Spodoptera frugiperda Sf-9 cells, insect Tricoplusia ni larvae, and insect Drosophila melanogaster S2 cells. Due to the highly hydrophobic nature of hIL-2, the GFP/hIL-2 fusion protein was expressed as an inclusion body in the E. coli system, resulting in minimal green fluorescence; however, Western blot analysis revealed the proper fusion band. In all other cases, the fusion proteins were expressed intracellularly or secreted as a functional form; green fluorescence was observed in each of these expression systems. We determined the linear relationships between GFP fluorescence and hIL-2 concentration in each case and used these correlations for comparison of the various expression systems in terms of production yield, productivity, product solubility (for intracellular expression systems), secretion efficiency (for secretion systems), and even functionality by simple measurement of GFP fluorescence. Even though the culture conditions were not optimized for each expression system, this comparison can be used as preliminary criteria for the selection of a proper expression system for recombinant protein production.