Soluble expression of single-chain variable fragment (scFv) in Escherichia coli using superfolder green fluorescent protein as fusion partner

Colorimetric and chemiluminescent enzyme immunoassays based on the alkaline phosphatase-tagged single-chain variable fragment fusion tracer for detecting zearalenone in agro-products

Zearalenone (ZEN) is a non-steroidal estrogenic mycotoxin and seriously threatens food safety, which requires rapid and sensitive detection methods for monitoring ZEN in agro-products. Herein, an alkaline phosphatase-tagged single-chain variable fragment fusion protein (ALP-scFv) was used as a bifunctional tracer to develop a colorimetric enzyme immunoassay (CEIA) and a chemiluminescent enzyme immunoassay (CLEIA) for ZEN. In addition, the interactions between scFv and ZEN were exploited by computer-assisted simulation, and four key amino acid sites were preliminarily identified. After optimization, the CEIA and CLEIA exhibited a limit of detection of 0.02 and 0.006 ng/mL, respectively. Furthermore, both methods showed favorable accuracy in recovery experiments and good selectivity in cross reactions. Moreover, the detection results of the actual samples from both methods correlated well with those from high-performance liquid chromatography. Overall, the ALP-scFv fusion tracer-based CEIA and CLEIA are demonstrated as reliable tools for ZEN detection in food.

A flexible 'plug and play' bicistronic construct and its application in the screening of protein expression system in Escherichia coli

The bicistronic expression system that utilizes fluorescent reporters has been demonstrated to be a straightforward method for detecting recombinant protein expression levels, particularly when compared to polyacrylamide gel electrophoresis and immunoblot analysis, which are tedious and labor-intensive. However, existing bicistronic reporter systems are less capable of quantitative measurement due to the lag in reporter expression and its negative impact on target protein. In this work, a plug and play bicistronic construct using mCherry as reporter was applied in the screening of optimal replicon and promoter for Sortase expression in Escherichia coli (E. coli). The bicistronic construct allowed the reporter gene and target open reading frame (ORF) to be co-transcribed under the same promoter, resulting in a highly positive quantitative correlation between the expression titer of Sortase and the fluorescent intensity (R2 > 0.97). With the correlation model, the titer of target protein can be quantified by noninvasively measuring the fluorescent intensity. On top of this, the expression of reporter has no significant effect on the yield of target protein, thus favoring a plug and play design for removing reporter gene to generate a plain plasmid for industrial use.

Engineering of Unspecific Peroxygenases Using a Superfolder-Green-Fluorescent-Protein-Mediated Secretion System in Escherichia coli

Unspecific peroxygenases (UPOs), secreted by fungi, demonstrate versatility in catalyzing challenging selective oxyfunctionalizations. However, the number of peroxygenases and corresponding variants with tailored selectivity for a broader substrate scope is still limited due to the lack of efficient engineering strategies. In this study, a new unspecific peroxygenase from Coprinopsis marcescibilis (CmaUPO) is identified and characterized. To enhance or reverse the enantioselectivity of wildtype (WT) CmaUPO catalyzed asymmetric hydroxylation of ethylbenzene, CmaUPO was engineered using an efficient superfolder-green-fluorescent-protein (sfGFP)-mediated secretion system in Escherichia coli. Iterative saturation mutagenesis (ISM) was used to target the residual sites lining the substrate tunnel, resulting in two variants: T125A/A129G and T125A/A129V/A247H/T244A/F243G. The two variants greatly improved the enantioselectivities [21% ee (R) for WT], generating the (R)-1-phenylethanol or (S)-1-phenylethanol as the main product with 99% ee (R) and 84% ee (S), respectively. The sfGFP-mediated secretion system in E. coli demonstrates applicability for different UPOs (AaeUPO, CciUPO, and PabUPO-I). Therefore, this developed system provides a robust platform for heterologous expression and enzyme engineering of UPOs, indicating great potential for their sustainable and efficient applications in various chemical transformations.

A one-step immunoassay based on switching peptides for diagnosis of porcine epidemic diarrhea virus (PEDV) using screened Fv-antibodies

In this study, a one-step immunoassay for porcine epidemic diarrhea virus (PEDV) based on Fv-antibodies and switching peptides was developed, and the assay results of PEDV were obtained by just mixing samples without any further reaction or washing steps. The Fv-antibodies with binding affinity to the spike protein of PEDV were screened from the Fv-antibody library using the receptor-binding domain (RBD) of the spike protein as a screening probe. Screened Fv-antibodies with binding affinities to the RBD antigen were expressed, and the binding constants (KD) were calculated to be 83-142 nM. The one-step immunoassay for the detection of PEDV was configured as a displacement immunoassay using a fluorescence-labeled switching peptide. The one-step immunoassay based on switching peptides was performed using PEDV, and the limit of detection (LOD) values for PEDV detection were estimated to be Ct = 39.7-36.4. Compared with the LOD value for a conventional lateral flow immunoassay (Ct = 33.0), the one-step immunoassay showed a remarkably improved LOD for the detection of PEDV. Finally, the interaction between the screened Fv-antibodies and the PEDV RBD was investigated using docking simulations and compared with the amino acid sequences of the receptors on host cells, such as aminopeptidase N (APN) and angiotensin-converting enzyme-2 (ACE-2).

Monocarboxylate transporter-1 (MCT-1) inhibitors screened from autodisplayed FV-antibody library

Monocarboxylate transporter-1 (MCT-1) inhibitors were screened from the Fv-antibody library, which contained complementary determining region 3 with randomized amino acid sequences (11 residues) through site-directed mutagenesis. Fv-antibodies against MCT-1 were screened from the autodisplayed Fv-antibody library. Two clones were screened, and the binding affinity (KD) against MCT-1 was estimated using flow cytometry. The screened Fv-antibodies were expressed as soluble fusion proteins (Fv-1 and Fv-2) and the KD for MCT-1 was estimated using the SPR biosensor. The inhibitory activity of the expressed Fv-antibodies was observed in HEK293T and Jurkat cell lines by measuring intracellular pH and lactate accumulation. The level of cell viability in HEK293T and Jurkat cell lines was decreased by the inhibitory activity of the expressed Fv-antibodies. The binding properties of the Fv-antibodies to MCT-1 were analyzed using molecular docking simulations. Overall, the results showed that the screened Fv-antibodies against MCT-1 from the Fv-antibody library had high binding affinity and inhibitory activity against MCT-1, which could be used as potential therapeutic drug candidates for the MCT-1 inhibitor.

A novel method for high level production of protein glutaminase by sfGFP tag in Bacillus subtilis

Protein glutaminase (PG; EC 3.5.1.44) is a novel deamidase that helps to improve functional properties of food proteins. Currently, the highest activated PG enzyme activity was 26 U/mg when recombinantly expressed via the twin-arginine translocation (Tat) pathway in Corynebacterium glutamicum. In this study, superfolder green fluorescent protein (sfGFP) was used to replace traditional signal peptides to facilitate efficient heterologous expression and secretion of Propeptide-Protein glutaminase (PP) in Bacillus subtilis. The fusion protein, sfGFP-PP, was secreted from 12 h of fermentation and reached its highest extracellular expression at 28 h, with a secretion efficiency of about 93 %. Moreover, when fusing sfGFP with PP at the N-terminus, it significantly enhances PG expression up to 26 U/mL by approximately 2.2-fold compared to conventional signal-peptides- guided PP with 11.9 U/mL. Finally, the PG enzyme activity increased from 26 U/mL to 36.9 U/mL after promoter and RBS optimization. This strategy not only provides a new approach to increase PG production as well as extracellular secretion but also offers sfGFP as an effective N-terminal tag for increased secreted production of difficult-to-express proteins.

One-step immunoassay of SARS-CoV-2 using screened Fv-antibodies and switching peptides

The Fv-antibodies were correponded to VH region of immunoglobulin G, which were composed of three complementarity determining regions (CDRs) for the specific binding of antigens. In this work, the Fv-antibodies against SARS-CoV-2 spike protein (SP) were screened from an autodisplayed Fv-antibody library which was expressed on E. coli outer membrane, and the receptor binding domain (RBD) of SP was used as a screening probe. The screened target clones were analyzed to have quantitative binding properties to the RBD, and the Fv-antibodies from the screened target clones were expressed as soluble proteins. The binding affinity (KD) of expressed Fv-antibodies to the RBD was estimated to be 70-85 nM using SPR biosensor. The specific binding properties of Fv-antibodies were analyzed for pseudo-virus particles with SARS-CoV-2 SP on the Lenti-virus envelope, such as wild type (Wuhan-1) and variants (Delta, Omicron BA.2, Omicron BA.4/5) using a SPR biosensor. The detection of real SARS-CoV-2 (Wild type, Wuhan-1) based on a SPR biosensor was also presented using the Fv-antibodies with the binding constant (KD) of cycle threshold value (Ct) = 33.8-32.9 (2.19-4.08 copies/μL) and LOD of 0.67-0.83 copies/μL (Ct = 35.5-35.2). Finally, one-step immunoassay based on switching peptide was demonstrated for the detection of the real SARS-CoV-2 (Wuhan-1) without any washing step. The binding constant (KD) was estimated to be Ct = 35.2-33.9 (0.83-2.04 copies/μL), and LOD was estimated to be 0.14-0.47 copies/μL (Ct = 37.8-36.0). Considering the LOD of the conventional RT-PCR (Ct = 35), the LOD of the one-step immunoassay based on the switching peptide was determined to be feasible for the medical diagnosis of COVID-19.

Immunoaffinity biosensors for the detection of SARS-CoV-1 using screened Fv-antibodies from an autodisplayed Fv-antibody library

The detection of severe acute respiratory syndrome coronavirus (SARS-CoV-1) was demonstrated using screened Fv-antibodies for SPR biosensor and impedance spectrometry. The Fv-antibody library was first prepared on the outer membrane of E. coli using autodisplay technology and the Fv-variants (clones) with a specific affinity toward the SARS-CoV-1 spike protein (SP) were screened using magnetic beads immobilized with the SP. Upon screening the Fv-antibody library, two target Fv-variants (clones) with a specific binding affinity toward the SARS-CoV-1 SP were determined and the Fv-antibodies on two clones were named "Anti-SP1" (with CDR3 amino acid sequence: 1GRTTG5NDRPD11Y) and "Anti-SP2" (with CDR3 amino acid sequence: 1CLRQA5GTADD11V). The binding affinities of the two screened Fv-variants (clones) were analyzed using flow cytometry and the binding constants (KD) were estimated to be 80.5 ± 3.6 nM for Anti-SP1 and 45.6 ± 8.9 nM for Anti-SP2 (n = 3). In addition, the Fv-antibody including three CDR regions (CDR1, CDR2, and CDR3) and frame regions (FRs) between the CDR regions was expressed as a fusion protein (Mw. 40.6 kDa) with a green fluorescent protein (GFP) and the KD values of the expressed Fv-antibodies toward the SP estimated to be 15.3 ± 1.5 nM for Anti-SP1 (n = 3) and 16.3 ± 1.7 nM for Anti-SP2 (n = 3). Finally, the expressed Fv-antibodies screened against SARS-CoV-1 SP (Anti-SP1 and Anti-SP2) were applied for the detection of SARS-CoV-1. Consequently, the detection of SARS-CoV-1 was demonstrated to be feasible using the SPR biosensor and impedance spectrometry utilizing the immobilized Fv-antibodies against the SARS-CoV-1 SP.

Production and applications of fluorobody from redox-engineered Escherichia coli

Efficient selection and production of antibody fragments in microbial systems remain to be a challenging process. To optimize microbial production of single-chain variable fragments (scFvs), we have chosen five model targets, 1) a hapten, Zearalenone (ZEN) mycotoxin, along with infectious agents 2) rabies virus, 3) Propionibacterium acnes, 4) Pseudomonas aeruginosa, and a cancer cell 5) acute myeloid leukemia cell line (HL-60). The scFv binders were affinity selected from a non-immunized human phage display scFv antibody library and genetically fused to the N-terminus of emerald green fluorescent protein (EmGFP). The scFv-EmGFP fusion constructs were subcloned into an expression vector, under the control of T7 promoter, C-terminally tagged with hexa-histidine and expressed in different Escherichia coli (E. coli) hosts. This enabled the detection of cells that expressed the correct scFv-EmGFP fusion, termed fluorobody, via bright fluorescent signal in the cytoplasm. Among the three E. coli hosts tested, an engineered E. coli B strain called SHuffle B that promotes disulfide bond formation in the cytoplasm appeared to be the most appropriate host. The recombinant fluorobodies were well expressed (2-8 mg/L), possessed the fluorescence property of EmGFP, and retained the ability to bind to their cognate targets. Their specific bindings were demonstrated by ELISA, fluorescence-linked immunosorbent assay (FLISA), flow cytometry, and fluorescent microscope imaging. The fluorobody expression platform in this study could be further adopted as a one-step immunostaining technique based on scFv, isolated from phage display library to numerous desired targets. KEY POINTS: • E. coli SHuffle express T7 is a suitable expression host for scFv-EmGFP (fluorobody) • Only the clones harboring scFv-EmGFP plasmid will show bright fluorescent signal • This platform can be used to produce fluorobodies for numerous purposes.

Specific N-terminal amino acids potentiate the periplasmic expression of single-chain variable fragments in Escherichia coli

Single-chain variable fragments (ScFvs) are important in therapy, diagnosis and research because of their elevated antigen affinity and low immunogenicity. At present, high-yield scFv expression in Escherichia coli is limited by insoluble aggregation in the reducing environment of the cytoplasm or low yields in the periplasm. Here we achieved increased expression of scFvs in the periplasm by inserting optimal amino acids between the signal peptide and scFv. We constructed an expression library with three random amino acids at the scFv N-terminus, screened this library with a single-step colony assay and identified the specific sequences that boosted periplasmic expression of scFvs.

Rational design of a Nivolumab-based ANTI-PD-1 single chain variable fragment that blocks the interaction between PD-1 expressed on T-CELLS and PD-L1 ON CHO cells

Antibodies that block the interaction between PD-1 expressing T-cells and cancer cells expressing PD-L1 play a central role in contemporary immunotherapy regimes [1-3]. We previously reported the isolation of a single chain variable fragment (scFv) of the monoclonal anti-PD-1 antibody Nivolumab, that binds to purified PD-1 and blocked its interaction with PD-L1 [4]. This anti-PD-1 scFv did not, however, function in a cell-based assay designed to detect the disruption of the PD-1/PD-L1 interaction, a result likely due to its poor solubility in tissue culture media. Herein we report that following a series of structure-based rational design analyses, including Aggreescan3D, we have isolated a variant of the anti-PD-1 scFv having significantly improved solubility in tissue culture medium. Moreover, this soluble anti-PD-1 scFv variant disrupted the interaction between PD-1 expressed on Jurkat Cells and PD-L1 expressed on CHO cells. These findings are discussed in terms of the related observation that the residues mutated to form the anti-PD-1 variant are conserved in many other scFvs; thus, the properties of a range of scFvs will likely be enhanced by similar mutations of the conserved residues.

1Progress, applications, challenges and prospects of protein purification technology

Protein is one of the most important biological macromolecules in life, which plays a vital role in cell growth, development, movement, heredity, reproduction and other life activities. High quality isolation and purification is an essential step in the study of the structure and function of target proteins. Therefore, the development of protein purification technologies has great theoretical and practical significance in exploring the laws of life activities and guiding production practice. Up to now, there is no forthcoming method to extract any proteins from a complex system, and the field of protein purification still faces significant opportunities and challenges. Conventional protein purification generally includes three steps: pretreatment, rough fractionation, and fine fractionation. Each of the steps will significantly affect the purity, yield and the activity of target proteins. The present review focuses on the principle and process of protein purification, recent advances, and the applications of these technologies in the life and health industry as well as their far-reaching impact, so as to promote the research of protein structure and function, drug development and precision medicine, and bring new insights to researchers in related fields.

A Novel Tandem-Tag Purification Strategy for Challenging Disordered Proteins

Intrinsically disordered proteins (IDPs) lack well-defined 3D structures and can only be described as ensembles of different conformations. This high degree of flexibility allows them to interact promiscuously and makes them capable of fulfilling unique and versatile regulatory roles in cellular processes. These functional benefits make IDPs widespread in nature, existing in every living organism from bacteria and fungi to plants and animals. Due to their open and exposed structural state, IDPs are much more prone to proteolytic degradation than their globular counterparts. Therefore, the purification of recombinant IDPs requires extra care and caution, such as maintaining low temperature throughout the purification, the use of protease inhibitor cocktails and fast workflow. Even so, in the case of long IDP targets, the appearance of truncated by-products often seems unavoidable. The separation of these unwanted proteins can be very challenging due to their similarity to the parent target protein. Here, we describe a tandem-tag purification method that offers a remedy to this problem. It contains only common affinity-chromatography steps (HisTrap and Heparin) to ensure low cost, easy access and scaling-up for possible industrial use. The effectiveness of the method is demonstrated with four examples, Tau-441 and two of its fragments and the transactivation domain (AF1) of androgen receptor.

SHTXTHHly, an extracellular secretion platform for the preparation of bioactive peptides and proteins in Escherichia coli

Background

In previous work, we developed an E. coli extracellular secretion platform XTHHly based on the hemolysin A secretion system. It can produce bioactive peptides with simple purification procedures. However, the wider application of this platform is limited by poor secretion efficiency.

Results

In this study, we first discovered a positive correlation between the isoelectric point (pI) value of the target protein and the secretion level of the XTHHly system. Given the extremely high secretion level of S tag, we fused it at the N-terminus and created a novel SHTXTHHly system. The SHTXTHHly system significantly increased the secretion levels of antimicrobial peptides (PEW300, LL37, and Aurein 1.2) with full bioactivities, suggesting its excellent capacity for secretory production of bioactive peptides. Furthermore, RGDS, IL-15, and alcohol dehydrogenase were successfully secreted, and their bioactivities were largely maintained in the fusion proteins, indicating the potential applications of the novel system for the rapid determination of protein bioactivities. Finally, using the SHTXTHHly system, we produced the monomeric Fc, which showed a high affinity for Fcγ Receptor I and mediated the antibody-dependent immunological effects of immune cells, demonstrating its potential applications in immunotherapies.

Conclusions

The SHTXTHHly system described here facilitates the secretory production of various types of proteins in E. coli. In comparison to previously reported expression systems, our work enlightens an efficient and cost-effective way to evaluate the bioactivities of target proteins or produce them.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01856-8.

Whole-Cell Display of Phosphotransferase in Escherichia coli for High-Efficiency Extracellular ATP Production

Adenosine triphosphate (ATP), as a universal energy currency, takes a central role in many biochemical reactions with potential for the synthesis of numerous high-value products. However, the high cost of ATP limits industrial ATP-dependent enzyme-catalyzed reactions. Here, we investigated the effect of cell-surface display of phosphotransferase on ATP regeneration in recombinant Escherichia coli. By N-terminal fusion of the super-folder green fluorescent protein (sfGFP), we successfully displayed the phosphotransferase of Pseudomonas brassicacearum (PAP-Pb) on the surface of E. coli cells. The catalytic activity of sfGFP-PAP-Pb intact cells was 2.12 and 1.47 times higher than that of PAP-Pb intact cells, when the substrate was AMP and ADP, respectively. The conversion of ATP from AMP or ADP were up to 97.5% and 80.1% respectively when catalyzed by the surface-displayed enzyme at 37 °C for only 20 min. The whole-cell catalyst was very stable, and the enzyme activity of the whole cell was maintained above 40% after 40 rounds of recovery. Under this condition, 49.01 mg/mL (96.66 mM) ATP was accumulated for multi-rounds reaction. This ATP regeneration system has the characteristics of low cost, long lifetime, flexible compatibility, and great robustness.

Microbial protein cell factories fight back?

The biopharmaceutical market is growing faster than ever, with two production systems competing for market dominance: mammalian cells and microorganisms. In recent years, based on the rise of antibody-based therapies, new biotherapeutic approvals have favored mammalian hosts. However, not only has extensive research elevated our understanding of microbes to new levels, but emerging therapeutic molecules also facilitate their use; thus, is it time for microbes to fight back? In this review, we answer this timely question by cross-comparing four microbial production hosts and examining the innovations made to both their secretion and post-translational modification (PTM) capabilities. Furthermore, we discuss the impact of tools, such as omics and systems biology, as well as alternative production systems and emerging biotherapeutics.

Drug Repurposing for the SARS-CoV-2 Papain-Like Protease

As the pathogen of COVID‐19, SARS‐CoV‐2 encodes two essential cysteine proteases that process the pathogen's two large polypeptide products pp1a and pp1ab in the human cell host to form 15 functionally important, mature nonstructural proteins. One of the two enzymes is papain‐like protease or PL^Pro. It possesses deubiquitination and deISGylation activities that suppress host innate immune responses toward SARS‐CoV‐2 infection. To repurpose drugs for PL^Pro, we experimentally screened libraries of 33 deubiquitinase and 37 cysteine protease inhibitors on their inhibition of PL^Pro. Our results showed that 15 deubiquitinase and 1 cysteine protease inhibitors exhibit strong inhibition of PL^Pro at 200 μM. More comprehensive characterizations revealed seven inhibitors GRL0617, SJB2‐043, TCID, DUB‐IN‐1, DUB‐IN‐3, PR‐619, and S130 with an IC₅₀ value below 40 μM and four inhibitors GRL0617, SJB2‐043, TCID, and PR‐619 with an IC₅₀ value below 10 μM. Among four inhibitors with an IC₅₀ value below 10 μM, SJB2‐043 is the most unique in that it does not fully inhibit PL^Pro but has a noteworthy IC₅₀ value of 0.56 μM. SJB2‐043 likely binds to an allosteric site of PL^Pro to convene its inhibition effect, which needs to be further investigated. As a pilot study, the current work indicates that COVID‐19 drug repurposing by targeting PL^Pro holds promise, but in‐depth analysis of repurposed drugs is necessary to avoid omitting critical allosteric inhibitors.

Recombinant active Peptides and their Therapeutic functions

Recombinant active peptides are utilized as diagnostic and biotherapeutics in various maladies and as bacterial growth inhibitors in the food industry. This consequently stimulated the need for recombinant peptides' production, which resulted in about 19 approved biotech peptides of 1-100 amino acids commercially available. While most peptides have been produced by chemical synthesis, the production of lengthy and complicated peptides comprising natural amino acids has been problematic with low quantity. Recombinant peptide production has become very vital, cost-effective, simple, environmentally friendly with satisfactory yields. Several reviews have focused on discussing expression systems, advantages, disadvantages, and alternatives strategies. Additionally, the information on the antimicrobial activities and other functions of multiple recombinant peptides is challenging to access and is scattered in literature apart from the food and drug administration (FDA) approved ones. From the reports that come to our knowledge, there is no existing review that offers substantial information on recombinant active peptides developed by researchers and their functions. This review provides an overview of some successfully produced recombinant active peptides of ≤100 amino acids by focusing on their antibacterial, antifungal, antiviral, anticancer, antioxidant, antimalarial, and immune-modulatory functions. It also elucidates their modes of expression that could be adopted and applied in future investigations. We expect that the knowledge available in this review would help researchers involved in recombinant active peptide development for therapeutic uses and other applications.

Soluble expression, purification, and secondary structure determination of human MESP1 transcription factor

Transcription factor MESP1 is a crucial factor regulating cardiac, hematopoietic, and skeletal myogenic development. Besides, it also contributes to the generation of functional cardiomyocytes. Here, we report the soluble expression and purification of the full-length human MESP1 protein from the heterologous system, which can be delivered into the target mammalian cells. To generate this biological macromolecule, we cloned its codon-optimized gene sequence fused to a nuclear localization sequence, a cell-penetrating peptide, and a His-tag into the protein expression vector and expressed in the bacterial system (E. coli strain BL21(DE3)). Subsequently, we have screened and identified the optimal expression parameters to obtain this recombinant fusion protein in soluble form from E. coli and examined its expression concerning the placement of fusion tags at either terminal. Further, we have purified this recombinant fusion protein to homogeneity under native conditions. Notably, this purified fusion protein has maintained its secondary structure after purification, primarily comprising α-helices and random coils. This molecular tool can potentially replace its genetic and viral forms in the cardiac reprogramming of fibroblasts to induce a cardiac transcriptional profile in an integration-free manner and elucidating its role in various biological processes and diseases. KEY POINTS: • Screening of the suitable gene construct was performed and identified. • Screening of optimal expression conditions was performed and identified. • Native purification of recombinant human MESP1 protein from E. coli was performed. • Recombinant MESP1 protein has retained its secondary structure after purification.

Effects of variable domain orientation on anti-HER2 single-chain variable fragment antibody expressed in the Escherichia coli cytoplasm

Single-chain variable fragment (scFv) antibodies have great potential for a range of applications including as diagnostic and therapeutic agents. However, production of scFvs is challenging because proper folding and activity depend on the formation of two intrachain disulfide bonds that do not readily form in the cytoplasm of living cells. Functional expression in bacteria therefore involves targeting to the more oxidizing periplasm, but yields in this compartment can be limiting due to secretion bottlenecks and the relatively small volume compared to the cytoplasm. In the present study, we evaluated an anti-HER2 scFv, which is specific for human epidermal growth receptor 2 (HER2) overexpressed in breast cancer, for functional expression in the cytoplasm of Escherichia coli strains BL21(DE3) and SHuffle T7 Express, the latter of which is genetically engineered for cytoplasmic disulfide bond formation. Specifically, we observed much greater solubility and binding activity with SHuffle T7 Express cells, which likely resulted from the more oxidative cytoplasm in this strain background. We also found that SHuffle T7 Express cells were capable of supporting high-level soluble production of anti-HER2 scFvs with intact disulfide bonds independent of variable domain orientation, providing further evidence that SHuffle T7 Express is a promising host for laboratory and preparative expression of functional scFv antibodies.

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.