Refolding techniques for recovering biologically active recombinant proteins from inclusion bodies

Gold Nanoparticles Augment N-Terminal Cleavage and Splicing Reactions in Mycobacterium tuberculosis SufB

Protein splicing is a self-catalyzed event where the intervening sequence intein cleaves off, joining the flanking exteins together to generate a functional protein. Attempts have been made to regulate the splicing rate through variations in temperature, pH, and metals. Although metal-regulated protein splicing has been more captivating to researchers, metals were shown to only inhibit splicing reactions that confine their application. This is the first study to show the effect of nanoparticles (NPs) on protein splicing. We found that gold nanoparticles (AuNPs) of various sizes can increase the splicing efficiency by more than 50% and the N-terminal cleavage efficiency by more than 45% in Mycobacterium tuberculosis SufB precursor protein. This study provides an effective strategy for engineering splicing-enhanced intein platforms. UV-vis absorption spectroscopy, isothermal titration calorimetry (ITC), and transmission electron microscopy (TEM) confirmed AuNP interaction with the native protein. Quantum mechanics/molecular mechanics (QM/MM) analysis suggested a significant reduction in the energy barrier at the N-terminal cleavage site in the presence of gold atom, strengthening our experimental evidence on heightened the N-terminal cleavage reaction. The encouraging observation of enhanced N-terminal cleavage and splicing reaction can have potential implementations from developing a rapid drug delivery system to designing a contemporary protein purification system.

Design, expression and functional assessment of novel engineered serratiopeptidase analogs with enhanced protease activity and thermal stability

Serratiopeptidase is a bacterial protease that has been used medicinally in variety of applications. Though, some drawbacks like sensitivity to environmental conditions and low penetration into cells limited its usage as a potent pharmaceutical agent. This study aimed to produce four novel truncated serratiopeptidase analogs with different lengths and possessing one disulfide bridge, in order to enhance protease activity and thermal stability of this enzyme. Mutagenesis and truncation were performed using specific primers by conventional and overlap PCR. The recombinant proteins were expressed in E. coli cells then purified and their protease activity and stability were checked at different pH and temperatures in comparison to the native form of the enzyme, Serra473. Enzyme activity assay showed that T306 [12-302 ss] was not further active which could be due to the large truncation. However, T344 [8-339 ss], T380 [8-339 ss] and T380 [12-302 ss] proteins showed higher proteolytic activity comparing to Serra473. These analogs were active at temperatures of 25-90 °C and pH 6-9.5. Interestingly, remaining enzyme activity of T344 [8-339 ss], T380 [8-339 ss] and T380 [12-302 ss] forms at 90 °C calculated as 87, 83 and 86 percent, respectively, comparing to the activity at room temperature. However, residual activity at the same conditions was 50% for the full length enzyme. Formation of disulfide bond in engineered serratiopeptidases could be the main reason for higher thermal stability compared to Serra473. Thermostability of T344 [8-339 ss], as the most thermostable designed serratiopeptidase, was additionally confirmed using differential scanning calorimetry.

Characterization of recombinant β subunit of human MUC4 mucin (rMUC4β)

MUC4 is a transmembrane mucin expressed on various epithelial surfaces, including respiratory and gastrointestinal tracts, and helps in their lubrication and protection. MUC4 is also aberrantly overexpressed in various epithelial malignancies and functionally contributes to cancer development and progression. MUC4 is putatively cleaved at the GDPH site into a mucin-like α-subunit and a membrane-tethered growth factor-like β-subunit. Due to the presence of several functional domains, the characterization of MUC4β is critical for understanding MUC4 biology. We developed a method to produce and purify multi-milligram amounts of recombinant MUC4β (rMUC4β). Purified rMUC4β was characterized by Far-UV CD and I-TASSER-based protein structure prediction analyses, and its ability to interact with cellular proteins was determined by the affinity pull-down assay. Two of the three EGF-like domains exhibited typical β-fold, while the third EGF-like domain and vWD domain were predominantly random coils. We observed that rMUC4β physically interacts with Ezrin and EGFR family members. Overall, this study describes an efficient and simple strategy for the purification of biologically-active rMUC4β that can serve as a valuable reagent for a variety of biochemical and functional studies to elucidate MUC4 function and generating domain-specific antibodies and vaccines for cancer immunotherapy.

A novel approach for the purification of aggregation prone proteins

The protein aggregation is one of the major challenges of the biotechnological industry, especially in the areas of development and commercialization of successful protein-based drug products. The inherent high aggregation tendency of proteins during various manufacturing processes, storage, and administration has significant impact upon the product quality, safety and efficacy. We have developed an interesting protein purification approach that separates the functionally active protein from inactive aggregates using a detergent concentration gradient. The C-terminally His tagged nucleocapsid protein of Crimean Congo Hemorrhagic fever virus (CCHFV) has high aggregation tendency and rapidly precipitates upon purification by NiNTA chromatography. Using the new purification approach reported here, the freshly purified protein by NiNTA chromatography was further processed using a detergent gradient. In this new purification approach the active protein is retained in the low detergent concentration zone while the inactive aggregates are promptly removed by their rapid migration to the high detergent concentration zone. The method prevented further aggregation and retained the RNA binding activity in the native protein despite numerous freeze thaw cycles. This simple approach prevents protein aggregation by rapidly separating the preformed early aggregates and creating the appropriate microenvironment for correctly folded proteins to retain their biological activity. It will be of potential importance to the biotechnological industry and other fields of protein biochemistry that routinely face the challenges of protein aggregation.

Evaluating the efficacy of immobilized metal affinity chromatography (IMAC) for host cell protein (HCP) removal from anti-HER2 scFv expressed in Escherichia coli

Host cell proteins (HCPs) are process-related impurities that have influence on product safety and efficacy. HCPs should effectively be removed by chromatographic steps in downstream purification process. In this study, we aimed to evaluate the efficacy of immobilized-metal affinity chromatography (IMAC) for separation of HCPs from anti-HER2 single chain fragment variable (scFv) expressed in E. coli. This study explored how different purification conditions including native, denaturing and hybrid affect HCP level in purified anti-HER2 scFv. Furthermore, the effects of NaCl concentration in wash buffer as well as imidazole concentration in wash and elution buffer on purification yield and HCP level in purified anti-HER2 scFv were evaluated. It was found that increasing imidazole concentration in wash and elution buffers in native conditions reduced the yield of anti-HER2 scFv purification. However, enhancing NaCl concentration in wash buffer in purification under native conditions led to significant increase in the amount of anti-HER2 scFv without any change in protein purity. Herein, none of the IMAC purification methods conducted on soluble cytoplasmic proteins under native conditions could reduce the amount of HCP to acceptable level. HCP content was only lowered to ˂ 10 ppm when inclusion bodies were purified under hybrid conditions. Furthermore, increasing imidazole concentration in wash buffer in purification under hybrid conditions led to significant increase in eluted anti-HER2 scFv concentration, while HCP content was also increased in this condition. Overall, purification under hybrid conditions using wash buffer containing 40 mM imidazole resulted in the highest yield and acceptable level of HCP.

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.

Purified recombinant human Chromogranin A N46 peptide with remarkable anticancer effect on human colon cancer cells

Human Chromogranin A N46 (CGA-N46) is a weak cationic α-helical peptide with wide-spectrum antibacterial, fungal, and anticancer activities. In this study, the recombinant human CGA-N46 peptide was expressed successfully in Escherichia coli. The gene of CGA-N46 was cloned into the expression vector pET-15b without a fusion tag at the N terminus and the peptide was expressed using Isopropyl-β-d-thiogalactoside (IPTG) as an inducer. Using 8 M guanidinium HCl, inclusion bodies containing the peptide were purified and solubilized. The rhCGA-N46 peptide was purified using Q-FF anion exchange column. The cytotoxicity of the purified rhCGA-N46 peptide was investigated on WI-38 human lung normal cell line. The anticancer activity was studied on human colon cancer cell line; HCT-116 cell line. Besides, the possible involvement of rhCGA-N46 peptide in regulating apoptotic signal pathways was analyzed by detecting the expression levels of BCL2, BID, and CAS-8 in the treated cells. The results concluded that the active peptide recovery was up to 41.98%. The purified rhCGA-N46 was safe on normal cells with IC₅₀ = 227.74 µg/ml (40.67 µM) and had an obvious anticancer effect on colon cancer cells with IC₅₀ = 1.997 µg/ml (356.6 nM). The expression level of BCL2 was down-regulated and BID and CAS-8 were up-regulated significantly in treated HCT-116 cells compared to untreated. In conclusion, the rhCGA-N46 peptide was produced successfully in the native form with promising anti-colon cancer activity.

Recombinant production of Trx-Ib-AMP4 and Trx-E50-52 antimicrobial peptides and antimicrobial synergistic assessment on the treatment of methicillin-resistant Staphylococcus aureus under in vitro and in vivo situations

PURPOSE

The production of alternative novel antimicrobial agents is considered an efficient way to cope with multidrug resistance among pathogenic bacteria. E50-52 and Ib-AMP4 antimicrobial peptides (AMPs) have illustrated great proven antibacterial effects. The aim of this study was recombinant production of these AMPs and investigation of their synergistic effects on methicillin-resistant Staphylococcus aureus (MRSA).

METHOD

At first, the codon optimized sequences of the Ib-AMP4 (UniProt: 024006 (PRO_0000020721), and E50-52 (UniProtKB: P85148) were individually ligated into the pET-32α vector and transformed into E. coli. After the optimization of production and purification steps, the MIC (Minimum inhibitory concentration), time kill and growth kinetic tests of recombinant proteins were determined against MRSA. Finally, the in vivo wound healing efficiency was tested.

RESULTS AND CONCLUSION

The recorded MIC of recombinant Trx-Ib-AMP4, Trx-E50-52 against MRSA bacterium were 0.375 and 0.0875 mg/mL respectively. The combination application of the produced AMPs by the checkerboard method confirmed their synergic activity. The results of the time-kill showed sharply decrease of the number of viable cells with over five time reductions in log₁₀ CFU/mL by the combination of Trx-E50-52 and Trx-IbAMP4 at 2 × MIC within 240 min. The growth kinetic results confirmed the combination of Trx-E50-52 and Trx-IbAMP4 had much greater success in the reduction of over 50 % of MRSA suspensions' turbidity within the first hour. Wound healing assay and histological analysis of infected mice treated with Trx-Ib-AMP4 or Trx-E50-52 compared with those treated with a combination of Trx-Ib-AMP4 and Trx-E50-52 showed significant synergic effects.

RNA-dependent assembly of chimeric antigen nanoparticles as an efficient H5N1 pre-pandemic vaccine platform

Highly pathogenic avian influenza viruses (HPAIVs) pose a significant threat to human health, with high mortality rates, and require effective vaccines. We showed that, harnessed with novel RNA-mediated chaperone function, hemagglutinin (HA) of H5N1 HPAIV could be displayed as an immunologically relevant conformation on self-assembled chimeric nanoparticles (cNP). A tri-partite monomeric antigen was designed including: i) an RNA-interaction domain (RID) as a docking tag for RNA to enable chaperna function (chaperna: chaperone + RNA), ii) globular head domain (gd) of HA as a target antigen, and iii) ferritin as a scaffold for 24 mer-assembly. The immunization of mice with the nanoparticles (~46 nm) induced a 25-30 fold higher neutralizing capacity of the antibody and provided cross-protection from homologous and heterologous lethal challenges. This study suggests that cNP assembly is conducive to eliciting antibodies against the conserved region in HA, providing potent and broad protective efficacy.

Harnessing the potential of bacterial oxidative folding to aid protein production

Protein folding is central to both biological function and recombinant protein production. In bacterial expression systems, which are easy to use and offer high protein yields, production of the protein of interest in its native fold can be hampered by the limitations of endogenous posttranslational modification systems. Disulfide bond formation, entailing the covalent linkage of proximal cysteine amino acids, is a fundamental posttranslational modification reaction that often underpins protein stability, especially in extracytoplasmic environments. When these bonds are not formed correctly, the yield and activity of the resultant protein are dramatically decreased. Although the mechanism of oxidative protein folding is well understood, unwanted or incorrect disulfide bond formation often presents a stumbling block for the expression of cysteine-containing proteins in bacteria. It is therefore important to consider the biochemistry of prokaryotic disulfide bond formation systems in the context of protein production, in order to take advantage of the full potential of such pathways in biotechnology applications. Here, we provide a critical overview of the use of bacterial oxidative folding in protein production so far, and propose a practical decision-making workflow for exploiting disulfide bond formation for the expression of any given protein of interest.

Fabrication of silica on chitin in ambient conditions using silicatein fused with a chitin-binding domain

High temperatures, harsh pH conditions, and toxic chemicals involved in the conventional synthesis and coating of silica limit the fabrication of new-generation hybrid materials immobilizing live cells and biomolecules such as enzymes and drugs. This hinders the application of inorganic-organic biohybrid materials in various fields, including bioelectronics, energy generation, and biomedicine. Silicatein, an enzyme found in siliceous sponges, catalyzes the polymerization of silica under mild conditions, that is, at room temperature and neutral pH. Silicatein was fused with a chitin-binding domain (ChBD) to selectively bind the fusion silicatein on the chitin material and with a small soluble tag called InakC, a hydrophilic protein from Pseudomonas syringae, to control the unfavorable aggregation of silicatein. The fusion silicatein was soluble in aqueous media and was successfully found to be adsorbed on the chitin material. The immobilized fusion silicatein acted as an interfacial catalyst to fabricate silica on chitin under ambient conditions. This technique can be used to fabricate inorganic-organic hybrid materials to immobilize biomolecules and can be applied to develop novel biocatalytic systems, biosensors, and tissue culture scaffolds.

Expression, Solubilization, Refolding and Final Purification of Recombinant Proteins as Expressed in the form of "Classical Inclusion Bodies" in E. coli

Escherichia coli has been most widely used for production of the recombinant proteins. Over-expression of the recombinant proteins is the mainspring of the inclusion bodies formation. The refolding of these proteins into bioactive forms is cumbersome and partly time-consuming. In the present study, we reviewed and discussed most issues regarding the recovery of "classical inclusion bodies" by focusing on our previous experiences. Performing proper methods of expression, solubilization, refolding and final purification of these proteins, would make it possible to recover higher amounts of proteins into the native form with appropriate conformation. Generally, providing mild conditions and proper refolding buffers, would lead to recover more than 40% of inclusion bodies into bioactive and native conformation.

Interferon-Based Biopharmaceuticals: Overview on the Production, Purification, and Formulation

The advent of biopharmaceuticals in modern medicine brought enormous benefits to the treatment of numerous human diseases and improved the well-being of many people worldwide. First introduced in the market in the early 1980s, the number of approved biopharmaceutical products has been steadily increasing, with therapeutic proteins, antibodies, and their derivatives accounting for most of the generated revenues. The success of pharmaceutical biotechnology is closely linked with remarkable developments in DNA recombinant technology, which has enabled the production of proteins with high specificity. Among promising biopharmaceuticals are interferons, first described by Isaacs and Lindenmann in 1957 and approved for clinical use in humans nearly thirty years later. Interferons are secreted autocrine and paracrine proteins, which by regulating several biochemical pathways have a spectrum of clinical effectiveness against viral infections, malignant diseases, and multiple sclerosis. Given their relevance and sustained market share, this review provides an overview on the evolution of interferon manufacture, comprising their production, purification, and formulation stages. Remarkable developments achieved in the last decades are herein discussed in three main sections: (i) an upstream stage, including genetically engineered genes, vectors, and hosts, and optimization of culture conditions (culture media, induction temperature, type and concentration of inducer, induction regimens, and scale); (ii) a downstream stage, focusing on single- and multiple-step chromatography, and emerging alternatives (e.g., aqueous two-phase systems); and (iii) formulation and delivery, providing an overview of improved bioactivities and extended half-lives and targeted delivery to the site of action. This review ends with an outlook and foreseeable prospects for underdeveloped aspects of biopharma research involving human interferons.

Selecting Subpopulations of High-Quality Protein Conformers among Conformational Mixtures of Recombinant Bovine MMP-9 Solubilized from Inclusion Bodies

A detailed workflow to analyze the physicochemical characteristics of mammalian matrix metalloproteinase (MMP-9) protein species obtained from protein aggregates (inclusion bodies-IBs) was followed. MMP-9 was recombinantly produced in the prokaryotic microbial cell factories Clearcoli (an engineered form of Escherichia coli) and Lactococcus lactis, mainly forming part of IBs and partially recovered under non-denaturing conditions. After the purification by affinity chromatography of solubilized MMP-9, four protein peaks were obtained. However, so far, the different conformational protein species forming part of IBs have not been isolated and characterized. Therefore, with the aim to link the physicochemical characteristics of the isolated peaks with their biological activity, we set up a methodological approach that included dynamic light scattering (DLS), circular dichroism (CD), and spectrofluorometric analysis confirming the separation of subpopulations of conformers with specific characteristics. In protein purification procedures, the detailed analysis of the individual physicochemical properties and the biological activity of protein peaks separated by chromatographic techniques is a reliable source of information to select the best-fitted protein populations.

A simple method to purify recombinant HCV core protein expressed in Pichia pastoris for obtaining virus-like particles and producing monoclonal antibodies

In this study, we describe an optimized method of obtaining virus-like particles (VLPs) of the recombinant hepatitis C virus (HCV) core protein (HCcAg) expressed in yeast cells (Pichia pastoris), which can be used for the construction of diagnostic test systems and vaccine engineering. The described simplified procedure was developed to enable in vitro self-assembly of HCcAg molecules into VLPs during protein purification. In brief, the HCcAg protein was precipitated from yeast cell lysates with ammonium sulfate and renatured by gel filtration on Sephadex G-25 under reducing conditions. VLPs were self-assembled after the removal of the reducing agent by gel filtration on Sephadex G-25. Protein purity and specificity were evaluated by SDS-PAGE and immunoblotting analysis. The molecular mass of VLPs and their relative quantity were measured by HPLC, followed by confirmation of VLPs production and estimation of their shape and size by transmission electron microscopy. As a result, we obtained recombinant HCcAg preparation (with ~90% purity) in the form of VLPs and monomers, which has been used to produce hybridomas secreting monoclonal antibodies (mAbs) against HCcAg.

Advances in monitoring and control of refolding kinetics combining PAT and modeling

Overexpression of recombinant proteins in Escherichia coli results in misfolded and non-active protein aggregates in the cytoplasm, so-called inclusion bodies (IB). In recent years, a change in the mindset regarding IBs could be observed: IBs are no longer considered an unwanted waste product, but a valid alternative to produce a product with high yield, purity, and stability in short process times. However, solubilization of IBs and subsequent refolding is necessary to obtain a correctly folded and active product. This protein refolding process is a crucial downstream unit operation-commonly done as a dilution in batch or fed-batch mode. Drawbacks of the state-of-the-art include the following: the large volume of buffers and capacities of refolding tanks, issues with uniform mixing, challenging analytics at low protein concentrations, reaction kinetics in non-usable aggregates, and generally low re-folding yields. There is no generic platform procedure available and a lack of robust control strategies. The introduction of Quality by Design (QbD) is the method-of-choice to provide a controlled and reproducible refolding environment. However, reliable online monitoring techniques to describe the refolding kinetics in real-time are scarce. In our view, only monitoring and control of re-folding kinetics can ensure a productive, scalable, and versatile platform technology for re-folding processes. For this review, we screened the current literature for a combination of online process analytical technology (PAT) and modeling techniques to ensure a controlled refolding process. Based on our research, we propose an integrated approach based on the idea that all aspects that cannot be monitored directly are estimated via digital twins and used in real-time for process control. KEY POINTS: • Monitoring and a thorough understanding of refolding kinetics are essential for model-based control of refolding processes. • The introduction of Quality by Design combining Process Analytical Technology and modeling ensures a robust platform for inclusion body refolding.

Interplay of Different Major Ampullate Spidroins during Assembly and Implications for Fiber Mechanics

Major ampullate (MA) spider silk has fascinating mechanical properties combining strength and elasticity. All known natural MA silks contain at least two or more different spidroins; however, it is unknown why and if there is any interplay in the spinning dope. Here, two different spidroins from Araneus diadematus are co-produced in Escherichia coli to study the possible dimerization and effects thereof on the mechanical properties of fibers. During the production of the two spidroins, a mixture of homo- and heterodimers is formed triggered by the carboxyl-terminal domains. Interestingly, homodimeric species of the individual spidroins self-assemble differently in comparison to heterodimers, and stoichiometric mixtures of homo- and heterodimers yield spidroin networks upon assembly with huge impact on fiber mechanics upon spinning. The obtained results provide the basis for man-made tuning of spinning dopes to yield high-performance fibers.

Comparison of Catalyzing Properties of Bacterial 4-α-Glucanotransferases Focusing on Their Cyclizing Activity

A newly cloned 4-α-glucanotransferase (αGT) from Deinococcus geothermalis and two typical bacterial αGTs from Thermus scotoductus and Escherichia coli (MalQ) were investigated. Among 4 types of catalysis, the cyclization activity of αGTs that produces cycloamylose (CA), a valuable carbohydrate making inclusion complexes, was intensively studied. The new αGT, DgαGT, showed close protein sequence to the αGT from T. scotoductus (TsαGT). MalQ was clearly separated from the other two αGTs in the phylogenetic and the conserved regions analyses. The reaction velocities of disproportionation, cyclization, coupling, and hydrolysis of three αGTs were determined. Intriguingly, MalQ exhibited more than 100-fold lower cyclization activity than the others. To lesser extent, the disproportionation activity of MalQ was relatively low. DgαGT and TsαGT showed similar kinetics results, but TsαGT had nearly 10-fold lower hydrolysis activity than DgαGT. Due to the very low cyclizing activity of MalQ, DgαGT and TsαGT were selected for further analyses. When amylose was treated with DgαGT or TsαGT, CA with a broad DP range was generated immediately. The DP distribution of CA had a bimodal shape (DP 7 and 27 as peaks) for the both enzymes, but larger DPs of CA quickly decreased in the DgαGT. Cyclomaltopentaose, a rare cyclic sugar, was produced at early reaction stage and accumulated as the reactions went on in the both enzymes, but the increase was more profound in the TsαGT. Taken together, we clearly demonstrated the catalytic differences between αGT groups from thermophilic and pathogenic bacteria that and showed that αGTs play different roles depending on their lifestyle.

Molecular Cloning, Purification and Characterization of Mce1R of Mycobacterium tuberculosis

The mce1 operon of Mycobacterium tuberculosis, important for lipid metabolism/transport, host cell invasion, modulation of host immune response and pathogenicity, is under the transcriptional control of Mce1R. Hence characterizing Mce1R is an important step for novel anti-tuberculosis drug discovery. The present study reports functional and in silico characterization of Mce1R. In this work, we have computationally modeled the structure of Mce1R and have validated the structure by computational and experimental methods. Mce1R has been shown to harbor the canonical VanR-like structure with a flexible N-terminal 'arm', carrying conserved positively charged residues, most likely involved in the operator DNA binding. The mce1R gene has been cloned, expressed, purified and its DNA-binding activity has been measured in vitro. The K_d value for Mce1R-operator DNA interaction has been determined to be 0.35 ± 0.02 µM which implies that Mce1R binds to DNA with moderate affinity compared to the other FCD family of regulators. So far, this is the first report for measuring the DNA-binding affinity of any VanR-type protein. Despite significant sequence similarity at the N-terminal domain, the wHTH motif of Mce1R exhibits poor conservancy of amino acid residues, critical for DNA-binding, thus results in moderate DNA-binding affinity. The N-terminal DNA-binding domain is structurally dynamic while the C-terminal domain showed significant stability and such profile of structural dynamics is most likely to be preserved in the structural orthologs of Mce1R. In addition to this, a cavity has been detected in the C-terminal domain of Mce1R which contains a few conserved residues. Comparison with other FCD family of regulators suggests that most of the conserved residues might be critical for binding to specific ligand. The max pKd value and drug score for the cavity are estimated to be 9.04 and 109 respectively suggesting that the cavity represents a suitable target site for novel anti-tuberculosis drug discovery approaches.

Effect of urea concentration on instant refolding of Nuclear Export Protein (NEP) from Influenza-A virus H1N1: A solution NMR based investigation

Nuclear-export-protein (NEP) plays multiple-functions during influenza virus replication-cycle and shows unique pattern of conserved residues, which altogether make NEP a potential target for developing novel anti-influenza drugs. However, the mechanistic structural biology of NEP has not been fully characterized so far owing to its tendency to aggregate in solution. As structural information is important to guide rational drug-discovery process; therefore, procedural optimization efforts are going on to achieve properly folded NEP in sub-millimolar concentrations for solution-NMR investigations. As a first step in this direction, the refolding-cum-aggregation behavior of recombinant-NEP with N-terminal purification-tag (referred here as NEPN) at different urea-concentrations has been investigated here by NMR-based methods. Several attempts were made to refold denatured NEP-N through step-dialysis. However, owing to its strong tendency to aggregate, excessive precipitation was observed at sub-higher levels of urea concentration (5.0 ± 1.0 M). Finally, we used drip-dilution method with 10.5 M urea-denatured NEP-N and were able to refold NEP-N instantly. The amide ¹H dispersion of 3.6 ppm (6.6-10.2 ppm) in the ¹⁵N-HSQC-spectra of instantly refolded NEP-N confirmed the folded state. This successful instant-refolding of NEP-N has been reported for the first-time and the underlying mechanism has been rationalized through establishing the complete backbone-resonance-assignments of NEP-N at 9.7 M urea-denatured state.

Efficient refolding of recombinant reteplase expressed in Escherichia coli strains using response surface methodology

Reteplase is a deleted variant of human tissue plasminogen activator with a complex structure containing nine disulfide bonds. Reteplase is expressed as inclusion bodies in Escherichia coli and needs the additional step of refolding for activation. In this study an experimental design was performed to find the optimal refolding condition for reteplase. The influence of 14 chemical additives was assessed by one factor at a time method and then Taguchi design followed by response surface methodology was employed to find compounds with most significant effects on reteplase refolding and their optimum concentration. We found that 0.13 M histidine, 1.64 M methionine, 0.33 M cysteine, and 0.34 M arginine in addition to the GSH/GSSG is the optimal condition for refolding of reteplase. We also investigated the refolding yield for inclusion bodies obtained from different E. coli strains and found that BL21 (DE3) has the best recovery yield in comparison to Rosetta-gami and Shuffle T7.

Development of recombinant human granulocyte colony-stimulating factor (nartograstim) production process in Escherichia coli compatible with industrial scale and with no antibiotics in the culture medium

The granulocyte colony-stimulating factor (G-CSF) is a hematopoietic cytokine that has important clinical applications for treating neutropenia. Nartograstim is a recombinant variant of human G-CSF. Nartograstim has been produced in Escherichia coli as inclusion bodies (IB) and presents higher stability and biological activity than the wild type of human G-CSF because of its mutations. We developed a production process of nartograstim in a 10-L bioreactor using auto-induction or chemically defined medium. After cell lysis, centrifugation, IB washing, and IB solubilization, the following three refolding methods were evaluated: diafiltration, dialysis, and direct dilution in two refolding buffers. Western blot and SDS-PAGE confirmed the identity of 18.8-kDa bands as nartograstim in both cultures. The auto-induction medium produced 1.17 g/L and chemically defined medium produced 0.95 g/L. The dilution method yielded the highest percentage of refolding (99%). After refolding, many contaminant proteins precipitated during pH adjustment to 5.2, increasing purity from 50 to 78%. After applying the supernatant to cation exchange chromatography (CEC), nartograstim recovery was low and the purity was 87%. However, when the refolding solution was applied to anion exchange chromatography followed by CEC, 91%-98% purity and 2.2% recovery were obtained. The purification process described in this work can be used to obtain nartograstim with high purity, structural integrity, and the expected biological activity. KEY POINTS: • Few papers report the final recovery of the purification process from inclusion bodies. • The process developed led to high purity and reasonable recovery compared to literature. • Nartograstim biological activity was demonstrated in mice using a neutropenia model.

Effective refolding of a cysteine rich glycoside hydrolase family 19 recombinant chitinase from Streptomyces griseus by reverse dilution and affinity chromatography

Conventional refolding methods are associated with low yields due to misfolding and high aggregation rates or very dilute proteins. In this study, we describe the optimization of the conventional methods of reverse dilution and affinity chromatography for obtaining high yields of a cysteine rich recombinant glycoside hydrolase family 19 chitinase from Streptomyces griseus HUT6037 (SgChiC). SgChiC is a potential biocontrol agent and a reference enzyme in the study and development of chitinases for various applications. The overexpression of SgChiC was previously achieved by periplasmic localization from where it was extracted by osmotic shock and then purified by hydroxyapatite column chromatography. In the present study, the successful refolding and recovery of recombinant SgChiC (r-SgChiC) from inclusion bodies (IB) by reverse dilution and column chromatography methods is respectively described. Approximately 8 mg of r-SgChiC was obtained from each method with specific activities of 28 and 52 U/mg respectively. These yields are comparable to that obtained from a 1 L culture volume of the same protein isolated from the periplasmic space of E. coli BL21 (DE3) as described in previous studies. The higher yields obtained are attributed to the successful suppression of aggregation by a stepwise reduction of denaturant from high, to intermediate, and finally to low concentrations. These methods are straight forward, requiring the use of fewer refolding agents compared with previously described refolding methods. They can be applied to the refolding of other cysteine rich proteins expressed as inclusion bodies to obtain high yields of actively folded proteins. This is the first report on the recovery of actively folded SgChiC from inclusion bodies.

Investigation of Supercharging as A Strategy to Enhance the Solubility and Plasminogen Cleavage Activity of Reteplase

Background

Reteplase, the recombinant form of tissue plasminogen activator, is a thrombolytic drug with outstanding characteristics, while demonstrating limited solubility and reduced plasminogen activation. Previously, we in silico designed a variant of Reteplase with positively supercharged surface, which showed promising stability, solubility and activity. This study was devoted to evaluation of the utility of supercharging technique for enhancing these characteristics in Reteplase.

Objective

To test the hypothesis that reinforced surface charge of a rationally-designed Reteplase variant will not compromise its stability, will increase its solubility, and will enhance its plasminogen cleavage activity.

Materials and Methods

Supercharged Reteplase coding sequence was cloned in pDest527 vector and expressed in E. coli BL21 (DE3). The expressed protein was extracted by cell disruption. Inclusion bodies were solubilized using guanidine hydrochloride, followed by dialysis for protein refolding. After confirmation with SDS-PAGE and western blotting, extracted proteins were assayed for solubility and tested for bioactivity.

Results

SDS-PAGE and western blot analysis confirmed the successful expression of Reteplase. Western blot experiments showed most of Reteplase expressed in the insoluble form. Plasminogen cleavage assay showed significantly higher activity of the supercharged variant than the wild type protein (P < 0.001). The stability of the supercharged variant was also comparable to the wild type.

Conclusion

Our findings, i.e. the contribution of the surface supercharging technique to retained stability, enhanced plasminogen cleavage activity, while inefficiently changed solubility of Reteplase, contain implications for future designs of soluble variants of this fibrinolytic protein drug.

Multi-epitope insert modulates solubility-based and chromatographic purification of human papilloma virus 16 L1-based vaccine without inhibiting virus-like particle assembly

The separation of heterogeneous protein mixtures has always been characterized by a trade-off between purity and yield. One way this issue has been addressed in the past is by recombinantly modifying protein to improve separations. Such modifications are mostly employed in the form of tags used specifically for affinity chromatography, though it is also possible to make changes to a protein that will have a sizeable impact on its hydrophobicity and charge/charge distribution. As such, it should also be possible to use protein tags to modulate phase separations and protein-resin binding kinetics when performing ion exchange chromatography. Here, we employed a three-step purification scheme on E. coli expressed, His-tagged, human papilloma virus 16 L1-based recombinant proteins (rHPV 16 L1) that consisted of an inclusion body (IB) wash step, a diethylaminoethyl (DEAE) anion exchange chromatography (AEX) step, and an immobilized metal affinity chromatography (IMAC) polishing step. Purification of the wild type rHPV 16 L1 protein (WT) was characterized by substantial losses during the IB wash but relatively high yield over the DEAE column. In contrast, purification of modified rHPV 16 L1, a chimeric version of the WT protein that had the last 34 amino acids replaced with an MHC class II multi-epitope insert derived from tetanus toxin and diphtheria toxin (WTΔC34-2TEp), was characterized by little to no losses in the IB wash but had a relatively low yield over the DEAE column. Since the fate of these proteins was to be used in vaccine formulations, it is important to note that the modifications made to the WTΔC34-2TEp protein had little to no effect on its ability to assemble into virus-like particles (VLPs). These results demonstrate that modifications of the WT protein via the recombinant insertion of immunofunctional polypeptides can modulate both phase-based separation and charge-based chromatographic processes. Additionally, incorporation of the specific, multi-epitope tag used in this study may prove to be beneficial in recombinant HPV vaccine development due to its potential to improve phase separation yield and vaccine immunogenicity without inhibiting VLP formation.

Optimization of Methods for the Production and Refolding of Biologically Active Disulfide Bond-Rich Antibody Fragments in Microbial Hosts

Antibodies have been used for basic research, clinical diagnostics, and therapeutic applications. Escherichia coli is one of the organisms of choice for the production of recombinant antibodies. Variable antibody genes have canonical and non-canonical disulfide bonds that are formed by the oxidation of a pair of cysteines. However, the high-level expression of an antibody is an inherent problem to the process of disulfide bond formation, ultimately leading to mispairing of cysteines which can cause misfolding and aggregation as inclusion bodies (IBs). This study demonstrated that fragment antibodies are either secreted to the periplasm as soluble proteins or expressed in the cytoplasm as insoluble inclusion bodies when expressed using engineered bacterial host strains with optimal culture conditions. It was observed that moderate-solubilization and an in vitro matrix that associated refolding strategies with redox pairing more correctly folded, structured, and yielded functionally active antibody fragments than the one achieved by a direct dilution method in the absence of a redox pair. However, natural antibodies have canonical and non-canonical disulfide bonds that need a more elaborate refolding process in the presence of optimal concentrations of chaotropic denaturants and redox agents to obtain correctly folded disulfide bonds and high yield antibodies that retain biological activity.

Efficient process development for high-level production, purification, formulation, and characterization of recombinant mecasermin in Escherichia coli

Overproduction of recombinant mecasermin was achieved by investigation of effect of three factors, temperature, inducer amount, and culture media, at three levels according to the Taguchi statistical design in Escherichia coli in a bench-scale bioreactor. In optimal conditions (induction temperature 28 °C, terrific broth with glucose (TB+G) medium, with 0.1 mM IPTG as inducer) 0.84 g/L mecasermin with expression levels of 38% of total protein and 4.13 g/L final dry cell biomass was produced, that is one of the highest values of recombinant protein has been reported in the batch system. The cell disruption was done by lysozyme pretreatment with sonication to the efficient purification of mecasermin. The isolated and washed inclusion bodies were solubilized in Gdn-HCl at pH 5.4 and folded with glutathione and purified with gel filtration. The purified rhIGF-1 (mecasermin) was formulated with arginine. Mecasermin protein remained t stable at 4 °C for up to 2 years. The quantitative and qualitative control indicated that mecasermin is expressed correctly (without the initial methionine by mass spectrometry), pure (without endotoxin and other protein impurities), correct folding (FTIR, RF-HPLC), monomer form (SEC-HPLC), and active (bioactivity test). Also, the purification results revealed that expression at low temperature results in the efficient purification of the overproduced mecasermin with high quantity and quality.

Biological Route to Fabricate Silica on Cellulose Using Immobilized Silicatein Fused with a Carbohydrate-Binding Module

Silicatein is an enzyme capable of catalyzing silica formation under mild conditions and is a promising catalyst for the fabrication of biohybrid materials. However, unfavorable aggregation of silicatein makes it unsuitable for use in material fabrication. In this study, a soluble protein tag (ProS2) and a carbohydrate-binding module (CBM) were used to develop a soluble and cellulose-binding fusion silicatein, ProS2-Sil-CBM, which can be efficiently immobilized on cellulose to form silica on it. ProS2-Sil-CBM was soluble in aqueous media and strongly bound to cellulose. ProS2-Sil-CBM bound on cellulose catalyzed the formation of a silica layer on the cellulose in the presence of tetraethyl orthosilicate as the substrate. Scanning electron microscopy (SEM) and surface elemental analysis confirmed the formation of silica on cellulose. This technique can be used to fabricate inorganic-organic hybrid materials to immobilize biomolecules and can be applied to develop novel biocatalytic systems, biosensors, and tissue culture scaffolds.

Oriented immobilization of basic fibroblast growth factor: Bioengineered surface design for the expansion of human mesenchymal stromal cells

E. coli expressed recombinant basic fibroblast growth factor (bFGF) with histidine-tag (bFGF-His) was immobilized onto the surface of a glass plate modified with a Ni(II)-chelated alkanethiol monolayer. The immobilization is expected to take place through the coordination between Ni(II) and His-tag. The bFGF-immobilized surface was exposed to citrate buffer solution to refold in situ the surface-immobilized bFGF. The secondary structure of immobilized bFGF-His was analyzed by solid-phase circular dichroism (CD) spectroscopy. Immortalized human mesenchymal stromal cells (hMSCs) were cultured on the bFGF-His-immobilized surface to examine their proliferation. CD spectroscopy revealed that the immobilized bFGF initially exhibited secondary structure rich in α-helix and that the spectrum was gradually transformed to exhibit the formation of β-strands upon exposure to citrate buffer solution, approaching to the spectrum of native bFGF. The rate of hMSC proliferation was 1.2-fold higher on the bFGF-immobilized surface treated with in situ citrate buffer, compared to the polystyrene surface. The immobilized bFGF-His treated in situ with citrate buffer solution seemed to be biologically active because its secondary structure approached its native state. This was well demonstrated by the cell culture experiments. From these results we conclude that immobilization of bFGF on the culture substrate serves to enhance proliferation of hMSCs.

Built-in RNA-mediated chaperone (chaperna) for antigen folding tailored to immunized hosts

High‐quality antibody (Ab) production depends on the availability of immunologically relevant antigens. We present a potentially universal platform for generating soluble antigens from bacterial hosts, tailored to immunized animals for Ab production. A novel RNA‐dependent chaperone, in which the target antigen is genetically fused with an RNA‐interacting domain (RID) docking tag derived from the immunized host, promotes the solubility and robust folding of the target antigen. We selected the N‐terminal tRNA‐binding domain of lysyl‐tRNA synthetase (LysRS) as the RID for fusion with viral proteins and demonstrated the expression of the RID fusion proteins in their soluble and native conformations; immunization predominantly elicited Ab responses to the target antigen, whereas the “self” RID tag remained nonimmunogenic. Differential immunogenicity of the fusion proteins greatly enriched and simplified the screening of hybridoma clones of monoclonal antibodies (mAbs), enabling specific and sensitive serodiagnosis of MERS‐CoV infection. Moreover, mAbs against the consensus influenza hemagglutinin stalk domain enabled a novel assay for trivalent seasonal influenza vaccines. The Fc‐mediated effector function was demonstrated, which could be harnessed for the design of next‐generation “universal” influenza vaccines. The nonimmunogenic built‐in antigen folding module tailored to a repertoire of immunized animal hosts will drive immunochemical diagnostics, therapeutics, and designer vaccines.

A simplified method for the efficient purification and refolding of recombinant human TRAIL

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) belongs to the TNF cytokine superfamily that specifically induces apoptosis in a broad spectrum of human cancer cell lines but not in most healthy cells. The antitumor potential of recombinant human TRAIL (rhTRAIL) has attracted great attention among biologists and oncologists. However, attempts to express rhTRAIL in Escherichia coli often results in limited yield of bioactive protein due to the formation of inclusion bodies (IBs), which are dense insoluble particulate protein aggregates inside cells. We describe herein a highly simplified method to produce pure bioactive rhTRAIL using E. coli. The method is straightforward and requires only basic laboratory equipment, with highly efficient purification and high yield of renaturation, and may also be applied to produce other proteins that form IBs in E. coli.

Efficacy of orally administered porcine epidemic diarrhea vaccine-loaded hydroxypropyl methylcellulose phthalate microspheres and RANKL-secreting L. lactis

Here, we examined the efficacy of are combinant subunit antigen-based oral vaccine for preventing porcine epidemic diarrhea virus (PEDV). First, we generated a soluble recombinant partial spike S1 protein (aP2) from PEDV in E. coli and then evaluated the utility of aP2 subunit vaccine-loaded hydroxypropyl methylcellulose phthalate microspheres (HPMCP) and RANKL-secreting L. lactis (LLRANKL) as a candidate oral vaccine in pregnant sows. Pregnant sows were vaccinated twice (with a 2 week interval between doses) at 4 weeks before farrowing. Titers of virus-specific IgA antibodies in colostrum, and neutralizing antibodies in serum, of sows vaccinated with HPMCP (aP2) plus LL RANKL increased significantly at 4 weeks post-first vaccination. Furthermore, the survival rate of newborn suckling piglets delivered by sows vaccinated with HPMCP (aP2) plus LL RANKL was similar to that of piglets delivered by sows vaccinated with a commercial killed porcine epidemic diarrhea virus (PED) vaccine. The South Korean government promotes a PED vaccine program (live-killed-killed) to increase the titers of IgA and IgG antibodies in pregnant sows and prevent PEDV. The oral vaccine strategy described herein, which is based on a safe and efficient recombinant subunit antigen, is an alternative PED vaccination strategy that could replace the traditional strategy, which relies on attenuated live oral vaccines or artificial infection with virulent PEDV.

Aggregation-prone peptides modulate activity of bovine interferon gamma released from naturally occurring protein nanoparticles

Efficient protocols for the production of recombinant proteins are indispensable for the development of the biopharmaceutical sector. Accumulation of recombinant proteins in naturally-occurring protein aggregates is detrimental to biopharmaceutical development. In recent years, the view of protein aggregates has changed with the recognition that they are a valuable source of functional recombinant proteins. In this study, bovine interferon-gamma (rBoIFN-γ) was engineered to enhance the formation of protein aggregates, also known as protein nanoparticles (NPs), by the addition of aggregation-prone peptides (APPs) in the generally recognized as safe (GRAS) bacterial Lactococcus lactis expression system. The L6K2, HALRU and CYOB peptides were selected to assess their intrinsic aggregation capability to nucleate protein aggregation. These APPs enhanced the tendency of the resulting protein to aggregate at the expense of total protein yield. However, fine physico-chemical characterization of the resulting intracellular protein NPs, the protein released from them and the protein purified from the soluble cell fraction indicated that the compactability of protein conformations was directly related to the biological activity of variants of IFN-γ, used here as a model protein with therapeutic potential. APPs enhanced the aggregation tendency of fused rBoIFN-γ while increasing compactability of protein species. Biological activity of rBoIFN-γ was favored in more compacted conformations. Naturally-occurring protein aggregates can be produced in GRAS microorganisms as protein depots of releasable active protein. The addition of APPs to enhance the aggregation tendency has a positive impact in overall compactability and functionality of resulting protein conformers.

Mutagenesis-Based Characterization and Improvement of a Novel Inclusion Body Tag

Whereas, bacterial inclusion bodies (IBs) for long were regarded as undesirable aggregates emerging during recombinant protein production, they currently receive attention as promising nanoparticulate biomaterials with diverse applications in biotechnology and biomedicine. We previously identified ssTorA, a signal sequence that normally directs protein export via the Tat pathway in E. coli, as a tag that induces the accumulation of fused proteins into IBs under overexpression conditions. Here, we used targeted mutagenesis to identify features and motifs being either critical or dispensable for IB formation. We found that IB formation is neither related to the function of ssTorA as a Tat-signal sequence nor is it a general feature of this family of signal sequences. IB formation was inhibited by co-overexpression of ssTorA binding chaperones TorD and DnaK and by amino acid substitutions that affect the propensity of ssTorA to form an α-helix. Systematic deletion experiments identified a minimal region of ssTorA required for IB formation in the center of the signal sequence. Unbiased genetic screening of a library of randomly mutagenized ssTorA sequences for reduced aggregation properties allowed us to pinpoint residues that are critical to sustain insoluble expression. Together, the data point to possible mechanisms for the aggregation of ssTorA fusions. Additionally, they led to the design of a tag with superior IB-formation properties compared to the original ssTorA sequence.

A panel of recombinant proteins from human-infective Plasmodium species for serological surveillance

Background

Malaria remains a global health problem and accurate surveillance of Plasmodium parasites that are responsible for this disease is required to guide the most effective distribution of control measures. Serological surveillance will be particularly important in areas of low or periodic transmission because patient antibody responses can provide a measure of historical exposure. While methods for detecting host antibody responses to Plasmodium falciparum and Plasmodium vivax are well established, development of serological assays for Plasmodium knowlesi, Plasmodium ovale and Plasmodium malariae have been inhibited by a lack of immunodiagnostic candidates due to the limited availability of genomic information.

Methods

Using the recently completed genome sequences from P. malariae, P. ovale and P. knowlesi, a set of 33 candidate cell surface and secreted blood-stage antigens was selected and expressed in a recombinant form using a mammalian expression system. These proteins were added to an existing panel of antigens from P. falciparum and P. vivax and the immunoreactivity of IgG, IgM and IgA immunoglobulins from individuals diagnosed with infections to each of the five different Plasmodium species was evaluated by ELISA. Logistic regression modelling was used to quantify the ability of the responses to determine prior exposure to the different Plasmodium species.

Results

Using sera from European travellers with diagnosed Plasmodium infections, antigens showing species-specific immunoreactivity were identified to select a panel of 22 proteins from five Plasmodium species for serological profiling. The immunoreactivity to the antigens in the panel of sera taken from travellers and individuals living in malaria-endemic regions with diagnosed infections showed moderate power to predict infections by each species, including P. ovale, P. malariae and P. knowlesi. Using a larger set of patient samples and logistic regression modelling it was shown that exposure to P. knowlesi could be accurately detected (AUC = 91%) using an antigen panel consisting of the P. knowlesi orthologues of MSP10, P12 and P38.

Conclusions

Using the recent availability of genome sequences to all human-infective Plasmodium spp. parasites and a method of expressing Plasmodium proteins in a secreted functional form, an antigen panel has been compiled that will be useful to determine exposure to these parasites.

Bacterial sugar-binding protein as a one-step affinity purification tag on dextran-containing resins

Marinobacter hydrocarbonoclasticus is an oil-eating bacterium that possesses a large adhesion protein (MhLap) with the potential to bind extracellular ligands. One of these ligand-binding modules is the ~20-kDa PA14 domain (MhPA14) that has affinity for glucose-based carbohydrates. Previous studies showed this sugar-binding domain is retained on dextran-based size-exclusion resins during chromatography, requiring the introduction of glucose or EDTA to remove the protein from the column. Given the ready availability of such size-exclusion resins in biochemistry laboratories, this study explores the use of MhPA14 as an affinity tag for recombinant protein purification. Two different fusion proteins were tested: 1) Green fluorescent protein (GFP) linked to the N-terminus of the MhPA14 tag; and 2) the ice-binding domain from the Marinomonas primoryensis ice-binding protein (MpIBD) linked to the MhPA14 C-terminus by a TEV cut site. The GFP_MhPA14 fusion visibly bound to Superdex, Sephadex, and Sephacryl resins, but did not bind to Sepharose. Using Superdex resin, dextran-affinity purification proved to be an effective one-step purification strategy for both proteins, superior to even nickel-affinity chromatography. Dextran-affinity chromatography was also the most effective method of separating the MhPA14 tag from MpIBD following TEV proteolysis, as compared to both nickel-affinity and ice-affinity methods. These results indicate that MhPA14 has potential for widespread use in recombinant protein purification.

Recent Developments in Bioprocessing of Recombinant Proteins: Expression Hosts and Process Development

Infectious diseases, along with cancers, are among the main causes of death among humans worldwide. The production of therapeutic proteins for treating diseases at large scale for millions of individuals is one of the essential needs of mankind. Recent progress in the area of recombinant DNA technologies has paved the way to producing recombinant proteins that can be used as therapeutics, vaccines, and diagnostic reagents. Recombinant proteins for these applications are mainly produced using prokaryotic and eukaryotic expression host systems such as mammalian cells, bacteria, yeast, insect cells, and transgenic plants at laboratory scale as well as in large-scale settings. The development of efficient bioprocessing strategies is crucial for industrial production of recombinant proteins of therapeutic and prophylactic importance. Recently, advances have been made in the various areas of bioprocessing and are being utilized to develop effective processes for producing recombinant proteins. These include the use of high-throughput devices for effective bioprocess optimization and of disposable systems, continuous upstream processing, continuous chromatography, integrated continuous bioprocessing, Quality by Design, and process analytical technologies to achieve quality product with higher yield. This review summarizes recent developments in the bioprocessing of recombinant proteins, including in various expression systems, bioprocess development, and the upstream and downstream processing of recombinant proteins.

Lactococcus lactis harbouring Ara h 2.02 alleviates allergen-specific Th2-associated responses in sensitized mice

AIM

To study the prophylactic effect of recombinant Lactococcus lactis (rLl) harbouring Ara h 2.02 peanut allergen, in sensitized and challenged mice.

METHODS AND RESULTS

Ara h 2.02 cDNA was cloned into pNZ8048 for heterologous expression in L. lactis. The purified recombinant allergen showed IgE binding comparable with native Ara h 2. Balb/c mice were fed with either recombinant (rLl), nonrecombinant L. lactis (Ll) or NaHCO₃ (Sham) prior to sensitization and challenged with rAra h 2.02, whereas the baseline group was only fed with Ll. Allergen-specific immunoglobulin and splenocyte cytokines responses were determined for each mouse. Mice fed with either Ll or rLl showed significant alleviation of IgE and IgG₁ compared to the Sham group. Despite no significant decrease in Th2 (IL-4, IL-13, IL-6) or increase in Th1 (IFN-γ) cytokines, both groups showed lower IL-10 level, while the IL-4 : IFN-γ ratio was significantly lower for rLl compared to Ll group.

CONCLUSIONS

Oral administration of rLl harbouring Ara h 2.02 demonstrated alleviation of Th2-associated responses in allergen-challenged mice and a possible added allergen-specific prophylactic effect.

SIGNIFICANCE AND IMPACT OF THE STUDY

Ara h 2.02 coupled with the intrinsic properties of probiotic L. lactis as a delivery vehicle can be explored for the development of a commercially scalable vaccine.

Modulation of the competition between renaturation and aggregation of lysozyme by additive mixtures

The effects of 17 kinds of additive mixtures have been studied on refolding and aggregation of a model protein, lysozyme. Most of the prepared mixtures were efficient in inhibiting aggregation of the protein, and, surprisingly, four novel additive mixtures, i.e., lactic acid: l-arginine, lactic acid: l-glutamine, choline chloride: lactic acid, and imidazolium salt: β-cyclodextrin as well as choline chloride: urea exhibited a more remarkable efficacy in suppressing aggregation. Among these, lactic acid: l-arginine was identified as the most efficient additive, and lactic acid: l-glutamine and choline chloride: lactic acid were inefficient to recover the enzyme activity. In contrast, choline chloride: ethylene glycol: imidazole, choline chloride: glycerol: imidazole, imidazole: betaine: ethylene glycol were found to be less effective mixtures in preventing enzyme aggregation. Totally, it was demonstrated that the protective effects of the mixtures were improved as their concentrations increased. The improvement was more remarkable for imidazolium salt: β-cyclodextrin and choline chloride: urea, where the denatured lysozyme was reactivated and recovered up to 85% of its initial activity by enhancing their concentrations from 1 to 5% (V/V). It is suggested that such solution additives may be further employed as artificial chaperones to assist protein folding and stability.

The Rocky Road From Fed-Batch to Continuous Processing With E. coli

Escherichia coli still serves as a beloved workhorse for the production of many biopharmaceuticals as it fulfills essential criteria, such as having fast doubling times, exhibiting a low risk of contamination, and being easy to upscale. Most industrial processes in E. coli are carried out in fed-batch mode. However, recent trends show that the biotech industry is moving toward time-independent processing, trying to improve the space-time yield, and especially targeting constant quality attributes. In the 1950s, the term "chemostat" was introduced for the first time by Novick and Szilard, who followed up on the previous work performed by Monod. Chemostat processing resulted in a major hype 10 years after its official introduction. However, enthusiasm decreased as experiments suffered from genetic instabilities and physiology issues. Major improvements in strain engineering and the usage of tunable promotor systems facilitated chemostat processes. In addition, critical process parameters have been identified, and the effects they have on diverse quality attributes are understood in much more depth, thereby easing process control. By pooling the knowledge gained throughout the recent years, new applications, such as parallelization, cascade processing, and population controls, are applied nowadays. However, to control the highly heterogeneous cultivation broth to achieve stable productivity throughout long-term cultivations is still tricky. Within this review, we discuss the current state of E. coli fed-batch process understanding and its tech transfer potential within continuous processing. Furthermore, the achievements in the continuous upstream applications of E. coli and the continuous downstream processing of intracellular proteins will be discussed.

Optimization of culture conditions for the expression of three different insoluble proteins in Escherichia coli

Recombinant protein expression for structural and therapeutic applications requires the use of systems with high expression yields. Escherichia coli is considered the workhorse for this purpose, given its fast growth rate and feasible manipulation. However, bacterial inclusion body formation remains a challenge for further protein purification. We analyzed and optimized the expression conditions for three different proteins: an anti-MICA scFv, MICA, and p19 subunit of IL-23. We used a response surface methodology based on a three-level Box-Behnken design, which included three factors: post-induction temperature, post-induction time and IPTG concentration. Comparing this information with soluble protein data in a principal component analysis revealed that insoluble and soluble proteins have different optimal conditions for post-induction temperature, post-induction time, IPTG concentration and in amino acid sequence features. Finally, we optimized the refolding conditions of the least expressed protein, anti-MICA scFv, using a fast dilution protocol with different additives, obtaining soluble and active scFv for binding assays. These results allowed us to obtain higher yields of proteins expressed in inclusion bodies. Further studies using the system proposed in this study may lead to the identification of optimal environmental factors for a given protein sequence, favoring the acceleration of bioprocess development and structural studies.