Unit Operation-Spanning Investigation of the Redox System

Cytoplasmic expression of recombinant proteins requiring disulfide bridges in Escherichia coli usually leads to the formation of insoluble inclusion bodies (IBs). The reason for this phenomenon is found in the reducing environment of the cytoplasm, preventing the formation of disulfide bridges and therefore resulting in inactive protein aggregates. However, IBs can be refolded in vitro to obtain the protein in its active conformation. In order to correctly form the required disulfide bridges, cystines are fully reduced during solubilization and, with the help of an oxidizing agent, the native disulfide bridges are formed during the refolding step. Here, a protocol to identify suitable redox conditions for solubilization and refolding is presented. For this purpose, a multivariate approach spanning the unit operations solubilization and refolding is used.

Refolding of bioactive human epidermal growth factor from E. coli BL21(DE3) inclusion bodies & evaluations on its in vitro & in vivo bioactivity

Human epidermal growth factor (hEGF) is a mitogenic protein widely used in pharmaceutical and cosmetic industries, thus recombinant DNA technology has been applied to meet the high demand for hEGF. The overexpression of recombinant protein in E. coli often leads to the formation of inclusion bodies (IBs). Mild solubilisation preserves the native secondary protein structure in IBs, thereby the high recovery of active protein from IBs. The redox system also plays a pivotal role in the formation of disulphide bonds during refolding of disulphide bond-containing protein. This study aimed to recover hEGF from bacterial IBs through freeze-thawing solubilisation and glutathione-based oxidative refolding. CBD-Ssp DnaB-hEGF fusion protein was expressed as IBs in E. coli, washed with Triton X-100 and urea to remove most protein contaminants, then the solubilised fusion protein was obtained by freeze-thawing with the addition of 2 M urea. The solubilised protein was subsequently refolded by intein cleavage via a glutathione-based redox system. The refolded hEGF demonstrated heat-resistant properties, interacted with specific antibodies on ELISA, stimulated keratinocyte proliferation and possessed significant in vivo wound healing properties on the 8^th day, confirming that hEGF was correctly folded. In summary, the protocol described is suitable for the recovery of refolded hEGF from bacterial IBs by mild solubilisation and oxidative refolding.

Expression and Refolding of the Plant Chitinase From Drosera capensis for Applications as a Sustainable and Integrated Pest Management

Recently, the study of chitinases has become an important target of numerous research projects due to their potential for applications, such as biocontrol pest agents. Plant chitinases from carnivorous plants of the genus Drosera are most aggressive against a wide range of phytopathogens. However, low solubility or insolubility of the target protein hampered application of chitinases as biofungicides. To obtain plant chitinase from carnivorous plants of the genus Drosera in soluble form in E.coli expression strains, three different approaches including dialysis, rapid dilution, and refolding on Ni-NTA agarose to renaturation were tested. The developed « Rapid dilution » protocol with renaturation buffer supplemented by 10% glycerol and 2M arginine in combination with the redox pair of reduced/oxidized glutathione, increased the yield of active soluble protein to 9.5 mg per 1 g of wet biomass. A structure-based removal of free cysteines in the core domain based on homology modeling of the structure was carried out in order to improve the soluble of chitinase. One improved chitinase variant (C191A/C231S/C286T) was identified which shows improved expression and solubility in E. coli expression systems compared to wild type. Computational analyzes of the wild-type and the improved variant revealed overall higher fluctuations of the structure while maintaining a global protein stability. It was shown that free cysteines on the surface of the protein globule which are not involved in the formation of inner disulfide bonds contribute to the insolubility of chitinase from Drosera capensis. The functional characteristics showed that chitinase exhibits high activity against colloidal chitin (360 units/g) and high fungicidal properties of recombinant chitinases against Parastagonospora nodorum. Latter highlights the application of chitinase from D. capensis as a promising enzyme for the control of fungal pathogens in agriculture.

Improved Production and Characterization of Recombinant Human Granulocyte Colony Stimulating Factor from E. coli under Optimized Downstream Processes

This work reports the upstream and downstream process of recombinant human granulocyte colony stimulating factor (rhG-CSF) expressed in Escherichia coli BL21 (DE3)pLysS. The fed batch mode was selected for the maximum output of biomass (6.4g/L) and purified rhG-CSF (136mg/L) under suitable physicochemical environment. The downstream processing steps viz., recovery, solubilization, refolding and concentration were optimized in this study. The maximum rhG-CSF inclusion bodies recovery yield (97%) was accomplished with frequent homogenization and sonication procedure. An efficient solubilization (96%) of rhG-CSF inclusion bodies were observed with 8M urea at pH 9.5. Refolding efficiency studies showed maximum refolding ⩾86% and ⩾84% at 20°C and pH 9 respectively. The renatured protein solution was concentrated, clarified and partially purified (⩾95%) by the cross flow filtration technique. The concentrated protein was further purified by a single step size exclusion chromatography with ⩾98% purity. The characterization of purified rhG-CSF molecular mass as evidenced by SDS-PAGE, western blot and LC/MS analysis was shown to be 18.8kDa. The secondary structure of rhG-CSF was evaluated by the CD spectroscopic technique based on the helical structural components. The biological activity of the purified rhG-CSF showed a similar activity of cell proliferation with the standard rhG-CSF. Overall, the results demonstrate an optimized downstream process for obtaining high yields of biologically active rhG-CSF.

Chaperon solvent plug design in size-exclusion chromatography protein refolding process

Although the chaperon solvent plug was reported as a strategy to reduce aggregation before the column inlet in SEC (size-exclusion chromatography) protein refolding process, the appropriate position at which sample injected and the volume of the chaperon solvent plug have not been elucidated. Therefore, the detail of chaperon solvent plug design was investigated in this work. Our results indicated that, to ensure good performances in the SEC refolding process, the appropriate front and tail volumes of chaperon solvent plug should be slightly larger than the optimal values, which depend on the flow dispersion from the injector to the column inlet. However, with the front volume more than the optimum, it could have an adverse effect on activity recovery but not the mass recovery, while no effect at all if the tail volume exceeded the optimum. Furthermore, it might be economical to replace the eluent (refolding buffer) after the tail of chaperon solvent plug with a cheaper one.

Engineered disulfides improve mechanical properties of recombinant spider silk

Nature's high-performance polymer, spider silk, is composed of specific proteins, spidroins, which form solid fibers. So far, fibers made from recombinant spidroins have failed in replicating the extraordinary mechanical properties of the native material. A recombinant miniature spidroin consisting of four poly-Ala/Gly-rich tandem repeats and a nonrepetitive C-terminal domain (4RepCT) can be isolated in physiological buffers and undergoes self assembly into macrofibers. Herein, we have made a first attempt to improve the mechanical properties of 4RepCT fibers by selective introduction of AA --> CC mutations and by letting the fibers form under physiologically relevant redox conditions. Introduction of AA --> CC mutations in the first poly-Ala block in the miniature spidroin increases the stiffness and tensile strength without changes in ability to form fibers, or in fiber morphology. These improved mechanical properties correlate with degree of disulfide formation. AA --> CC mutations in the forth poly-Ala block, however, lead to premature aggregation of the protein, possibly due to disulfide bonding with a conserved Cys in the C-terminal domain. Replacement of this Cys with a Ser, lowers thermal stability but does not interfere with dimerization, fiber morphology or tensile strength. These results show that mutagenesis of 4RepCT can reveal spidroin structure-activity relationships and generate recombinant fibers with improved mechanical properties.

Effect of sample loop dimension on lysozyme refolding in size-exclusion chromatography

The formation of misfolded protein aggregates, in particular inclusion bodies, has been widely considered as the major hindrance of good yield in refolding processes. To enhance the performance of protein refolding, extensive efforts were directed toward seeking out methods or means to reduce the aggregate production during the refolding process. Since simultaneous refolding and separation can be feasibly achieved within the packing matrices, size-exclusion chromatography (SEC) has been regarded as an efficient buffer exchange method to enhance protein refolding performance As of now, the effect of the process or operating parameters has yet to be thoroughly investigated. The present work is aimed at understanding how aggregate formation, as well as renaturation yield, varied with the diameter or length of sample loop in size-exclusion chromatography refolding process. Our results showed that not much difference was found in the patterns of aggregate formation for the contraction and the control cases. However, the formation of an additional peak was observed in the expansion cases. In addition, the amount of aggregates was not dependent on the sample loop diameter or length, but instead, influenced by injection volume and protein concentration. It was further concluded that a sample with large volume and low concentration was preferable for refolding process. We believe that the outcome from this work may shed light on the development of a more effective strategy for refolding processes.