RESUMO
AIMS: The Escherichia coli expression system is highly effective in producing recombinant proteins. However, there are some limitations in this system, especially in obtaining correctly folded forms of some complex proteins such as Fab fragments. To improve the solubility and folding quality of Fab fragments, we have examined the effect of simultaneous application of a SUMO fusion tag, EnBase® cultivation mode and a redox mutant strain in the E. coli expression system. METHODS AND RESULTS: A bicistronic gene construct was designed to express an antivascular endothelial growth factor (VEGF) Fab fragment as a model system. The construct contained a dual SUMO fusion gene fragment to encode SUMO-tagged heavy and light chains. While the expression of the construct in batch cultures of BL21 or SHuffle® transformants produced insoluble and unfolded products, the induction of the transformants in EnBase® medium resulted in soluble and correctly folded Fab fragment, reaching as high as 19% of the total protein in shuffle strain. The functional assays indicated that the biological activity of the target Fab is similar to the commercial anti-VEGF, Lucentis® . CONCLUSIONS: This study demonstrated that the combination of SUMO fusion technology, EnBase® cultivation system and recruiting a redox mutant of E. coli can efficiently enhance the solubility and productivity of recombinant Fab fragments. SIGNIFICANCE AND THE IMPACT OF THE STUDY: The presented strategy provides not only a novel method to produce soluble and active form of an anti-VEGF Fab but also may use in the efficient production of other antibody fragments.
RESUMO
AIMS: A novel chimeric-truncated form of tissue-type plasminogen activator (t-PA) with improved fibrin affinity and resistance to PAI was successfully produced in CHO expression system during our previous studies. Considering advantages of prokaryotic expression systems, the aim in this study was to produce the novel protein in Escherichia coli (BL21) strain and compare the protein potency in batch and fed-batch processes. METHODS AND RESULTS: The expression cassette for the novel t-PA was prepared in pET-28a(+). The E. coli expression procedure was compared in traditional batch and newly developed fed batch, EnBase(®) Flo system. The protein was purified in soluble format, and potency results were identified using Chromolize t-PA Assay Kit. The fed-batch fermentation mode, coupled with a Ni-NTA affinity purification procedure under native condition, resulted in higher amounts of soluble protein, and about a 30% of improvement in the specific activity of the resulted recombinant protein (46.66 IU mg(-1) ) compared to traditional batch mode (35.8 IU mg(-1) ). CONCLUSIONS: Considering the undeniable advantages of expression in the prokaryotic expression systems such as E. coli for recombinant protein production, applying alternative methods of cultivation is a promising approach. In this study, fed-batch cultivation methods showed the potential to replace miss-folded formats of protein with proper folded, soluble form with improved potency. SIGNIFICANCE AND IMPACT OF THE STUDY: Escherichia coli expression of recombinant proteins still counts for nearly 40% of marketed biopharmaceuticals. The major drawback of this system is the lack of appropriate post-translational modifications, which may cause potency loss/decline. Therefore, applying alternative methods of cultivation as investigated here is a promising approach to overcome potency decrease problem in this protein production system.
