How additives influence the refolding of immunoglobulin-folded proteins in a stepwise dialysis system. Spectroscopic evidence for highly efficient refolding of a single-chain Fv fragment

Identification of an Immunoglobulin Paratope Binding to Keratan Sulfate and Expression of a Single-Chain Derivative for Imaging

Keratan sulfate (KS) is a negatively charged carbohydrate linked to proteins. Several KS-bearing structural glycosaminoglycans participate to maintain the homeostasis of a functional extracellular matrix. Dysfunction of its biochemical composition and structure might therefore lead to pathological situations. For this reason, imaging of KS in tissues is an important diagnostic tool. Here, we describe the identification of the KS paratope derived from the ancestral anti-KS IgG mAb MZ15, as well as the engineering, functional recombinant expression in E. coli, and purification of an anti-KS single-chain variable fragment (ScFv). The ScFv enabled in vitro imaging of KS in cryosections of rat cornea by immunofluorescence microscopy comparable to the ancestral IgG MZ15.

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).

Nanofluidic point-of-care IgE test for subtropical grass pollen for rapid diagnosis of allergic rhinitis

BACKGROUND

Widening of subtropical climate zones globally and increasing grass-pollen exposure provide the impetus for developing a more precise and accessible diagnosis of allergy.

OBJECTIVE

To evaluate the utility of recombinant allergen components of Panicoideae and Chloridoideae pollens for specific IgE testing in a rapid, point-of-care device.

METHODS

Recombinant (r) Pas n 1 and Cyn d 1 were expressed, purified, and tested in the nanofluidic device for measuring serum specific IgE (spIgE) in a well-characterized Australian cohort. Concentrations and classes of spIgE to rPas n 1 and rCyn d 1, and total IgE were compared with skin prick test results and spIgE with grass pollen.

RESULTS

Correlations between commercial and academic laboratories for 21 sera were high for rPas n 1 spIgE (r = 0.695) and total IgE (r = 0.945). Higher spIgE to rPas n 1 and rCyn d 1 fluorescence was detected in the patients with grass-pollen allergy and with clinician-diagnosed allergic rhinitis (n = 134) than in participants with other allergies (n = 49) or no allergies (n = 23). Correlation between spIgE concentrations to rPas n 1 (r = 0.679) and rCyn d 1 (r = 0.548), with Bahia and Bermuda grass-pollen spIgE, respectively, was highly significant (p<0.0001). The positive/negative predictive agreements of spIgE classes for rPas n 1 (73%/82.5%) and rCyn d 1 (67.8%/66.3%) between the nanofluidic and ImmunoCAP measurements for Bahia and Bermuda grass pollen, respectively, were substantial.

CONCLUSION

Point-of-care nanofluidic tests for spIgE to rPas n 1 and rCyn d 1 could increase access to more precise clinical diagnosis for patients with allergies in subtropical regions.

A role and mechanism for redox sensing by SENP1 in β-cell responses to high fat feeding

Pancreatic β-cells respond to metabolic stress by upregulating insulin secretion, however the underlying mechanisms remain unclear. Here we show, in β-cells from overweight humans without diabetes and mice fed a high-fat diet for 2 days, insulin exocytosis and secretion are enhanced without increased Ca2+ influx. RNA-seq of sorted β-cells suggests altered metabolic pathways early following high fat diet, where we find increased basal oxygen consumption and proton leak, but a more reduced cytosolic redox state. Increased β-cell exocytosis after 2-day high fat diet is dependent on this reduced intracellular redox state and requires the sentrin-specific SUMO-protease-1. Mice with either pancreas- or β-cell-specific deletion of this fail to up-regulate exocytosis and become rapidly glucose intolerant after 2-day high fat diet. Mechanistically, redox-sensing by the SUMO-protease requires a thiol group at C535 which together with Zn+-binding suppresses basal protease activity and unrestrained β-cell exocytosis, and increases enzyme sensitivity to regulation by redox signals.

Small conformational changes in IgG1 detected as acidic charge variants by cation exchange chromatography

Fully characterizing the post-translational modifications present in charge variants of therapeutic monoclonal antibodies (mAbs), particularly acidic variants, is challenging and remains an open area of investigation. In this study, to test the possibility that chromatographically separated acidic fractions of therapeutic mAbs contain conformational variants, we undertook a mAb refolding approach using as a case study an IgG1 that contains many unidentified acidic peaks with few post-translational modifications, and examined whether different acidic peak fractions could be generated corresponding to these variants. The IgG1 drug substance was denatured by guanidine hydrochloride, without a reducing agent present, and gradually refolded by stepwise dialysis against arginine hydrochloride used as an aggregation suppressor. Each acidic chromatographic peak originally contained in the IgG1 drug substance was markedly increased by this stepwise refolding process, indicating that these acidic variants are conformational variants. However, no conformational changes were detected by small-angle X-ray scattering experiments for the whole IgG1, indicating that the conformational changes are minor. Chromatographic, thermal and fluorescence analyses suggested that the conformational changes are a localized denaturation effect centred around the aromatic amino acid regions. This study provides new insights into the characterization of acidic variants that are currently not fully understood.

Recent Advances in Overexpression of Functional Recombinant Lipases

Heterologous functional expression of the recombinant lipases is typically a bottleneck due to the expression in the insoluble fraction as inclusion bodies (IBs) which are in inactive form. Due to the importance of lipases in various industrial applications, many investigations have been conducted to discover suitable approaches to obtain functional lipase or increase the expressed yield in the soluble fraction. The utilization of the appropriate prokaryotic and eukaryotic expression systems, along with the suitable vectors, promoters, and tags, has been recognized as a practical approach. One of the most powerful strategies to produce bioactive lipases is using the molecular chaperones co-expressed along with the target protein's genes into the expression host to produce the lipase in soluble fraction as a bioactive form. The refolding of expressed lipase from IBs (inactive) is another practical strategy which is usually carried out through chemical and physical methods. Based on recent investigations, the current review simultaneously highlights strategies to express the bioactive lipases and recover the bioactive lipases from the IBs in insoluble form.

Expression and characterisation of human glycerol kinase: the role of solubilising agents and molecular chaperones

BACKGROUND

Glycerol kinase (GK; EC 2.7.1.30) facilitates the entry of glycerol into pathways of glucose and triglyceride metabolism and may play a potential role in Type 2 diabetes mellitus (T2DM). However, the detailed regulatory mechanisms and structure of the human GK are unknown.

METHODS

The human GK gene was cloned into the pET-24a(+) vector and over-expressed in Escherichia coli BL21 (DE3). Since the protein was expressed as inclusion bodies (IBs), various culture parameters and solubilising agents were used but they did not produce bioactive His-GK; however, co-expression of His-GK with molecular chaperones, specifically pKJE7, achieved expression of bioactive His-GK. The overexpressed bioactive His-GK was purified using coloumn chromatography and characterised using enzyme kinetics.

RESULTS

The overexpressed bioactive His-GK was purified apparently to homogeneity (∼295-fold) and characterised. The native His-GK was a dimer with a monomeric molecular weight of ∼55 kDa. Optimal enzyme activity was observed in TEA buffer (50 mM) at 7.5 pH. K+ (40 mM) and Mg2+ (2.0 mM) emerged as prefered metal ions for His-GK activity with specific activity 0.780 U/mg protein. The purified His-GK obeyed standard Michaelis-Menten kinetics with Km value of 5.022 µM (R2=0.927) for its substrate glycerol; whereas, that for ATP and PEP was 0.767 mM (R2=0.928) and 0.223 mM (R2=0.967), respectively. Other optimal parameters for the substrate and co-factors were also determined.

CONCLUSION

The present study demonstrates that co-expression of molecular chaperones assists with the expression of bioactive human GK for its characterisation.

Construction and evaluation of wild and mutant ofatumumab scFvs against the human CD20 antigen

Several monoclonal antibodies targeting the CD20 have been produced and Ofatumumab is a case in point. Although whole antibodies target cancer cells effectively, their applications are restricted in some ways. Single-chain fragment variable antibodies, rather than employing the entire structure of antibodies, have proven a practical approach for creating completely functional antigen-binding fragments. In current research, the DNA coding sequence of VL and VH of the wild and mutant forms of ofatumumab were joined with a flexible linker (GGGGS)3 separately. Using the E. coli BL21 (DE3) expression system, the VL-linker-VH genes were cloned into the pET-28 a (+), and the associated recombinant proteins were produced. Purified and refolded scFvs (scFv-C and scFv-V3) represented a concentration of around 0.7 mg/ml from 1 L of initial E. coli culture with a molecular weight of about 27 kDa. Affinity measurement disclosed anti-CD20 scFv-V3 possesses a higher affinity constant compared to anti-CD20 scFv-C. The recombinant scFvs exclusively attach to Raji cells but not to Jurkat cells, according to a cell-ELISA analysis. The MTT test signified anti-CD20 scFvs could affect cell viability in Raji cells but had no impact on Jurkat cells and also, Raji cells viability was affected more significantly by anti-CD20 scFv-V3.

Inclusion Bodies: Status Quo and Perspectives

Multiple E. coli cultivations, producing recombinant proteins, lead to the formation of inclusion bodies (IBs). IBs historically were considered as nondesired by-products, due to their time- and cost-intensive purification. Nowadays, many obstacles in IB processing can be overcome. As a consequence, several industrial processes with E. coli favor IB formation over soluble production options due to the high space time yields obtained. Within this chapter, we discuss the state-of-the art biopharmaceutical IB process, review its challenges, highlight the recent developments and perspectives, and also propose alternative solutions, compared to the state-of-the art processing.

Monoclonal antibodies (mAbs) and single chain variable fragment (scFv) antibodies targeting envelope protein VP28 of white spot syndrome virus provide protection against viral infection

White spot syndrome virus (WSSV) is extremely pathogenic and causes huge economic losses in the shrimp farming industry. Neutralizing antibodies against WSSV is expected to be an effective means of preventing infection with the virus. In the present study, eight monoclonal antibodies (mAbs) against VP28 were developed by immunizing BALB/c mice with WSSV-VP28 recombinant protein. Among them, three mAbs named 3B7, 2G3 and 5D2 were determined to be able to delay the mortality of WSSV-infected shrimp in vivo neutralization assay, suggesting their neutralizing ability against WSSV infection. Immunoblotting results showed that the three mAbs reacted specifically with native VP28 of WSSV, and could also recognize the virions in the gills of WSSV-infected shrimp by IFA. Furthermore, the single chain variable fragment (scFv) genes specific for WSSV-VP28 were cloned from the three hybridoma cells and expressed in Escherichia coli. After purification and refolding, three biologically active scFv recombinant proteins were all capable of recognizing the native VP28 of WSSV and delayed the mortality of WSSV-infected shrimp, indicating their neutralizing capacity against WSSV. Subsequently, the eukaryotic expression plasmids of three scFv genes were constructed and the transcriptional properties of expression vectors in shrimp were analyzed. Animal experiments also proved that the scFv eukaryotic expression plasmids were able to partially neutralize WSSV infection. Thus, the production of neutralizing mAb and recombinant scFv antibodies against WSSV has a promising therapeutic potential in prevention and treatment of white spot disease of shrimp.

Challenges for design of aggregation-resistant variants of granulocyte colony-stimulating factor

Non-native protein aggregation is a long-standing issue in pharmaceutical biotechnology. A rational design approach was used in order to identify variants of recombinant human granulocyte colony-stimulating factor (rhG-CSF) with lower aggregation propensity at solution conditions that are typical of commercial formulation. The approach used aggregation-prone-region (APR) predictors to select single amino acid substitutions that were predicted to decrease intrinsic aggregation propensity (IAP). The results of static light scattering temperature-ramps and chemical unfolding experiments demonstrated that none of the selected variants exhibited improved aggregation resistance, and the apparent conformational stability of each variant was lower than that of WT. Aggregation studies under partly denaturing conditions suggested that the IAP of at least one variant remained unaltered. Overall, this study highlights a general challenge in designing aggregation resistance for proteins, due to the need to accurately predict both APRs and conformational stability.

Immune adjuvant effects of interferon-gamma (IFN-γ) of flounder (Paralichthys olivaceus) against Edwardsiella tarda

IFN-γ plays a key role in T-cell activation and the establishment of the adaptive immune response, which has a potential as a cytokine adjuvant in the context of vaccination. In this study, we evaluated the immune adjuvant effects of two forms of flounder (Paralichthys olivaceus) IFN-γ, including pcDNA3.1-IFN-γ (pcIFN-γ) and recombinant IFN-γ (rIFN-γ), and comparatively analyzed the immune responses of flounder to E. tarda subunit vaccine rOmpV. The results showed that vaccination with rOmpV plus pcIFN-γ or rIFN-γ produced a relative percent survival of 57% and 71%, respectively, which were significantly higher than that of the control groups, rOmpV plus pcN3 (36%) or rHis (40%). Compared with the two control groups, vaccination with rOmpV plus pcIFN-γ or rIFN-γ could induce significantly higher levels of specific serum antibodies and sIg + lymphocytes in peripheral blood, spleen and head kidney, and significantly higher upregulated expressions of CD4-1, CD8α, IgM, MHC Ⅰα, MHC Ⅱα, IL-1β and TNF-α were also detected in rOmpV plus pcIFN-γ or rIFN-γ vaccinated fish. In addition, compared with pcIFN-γ, rOmpV co-vaccination with rIFN-γ elicited higher levels of sIg + lymphocytes, specific serum antibodies and several immune-related genes expressions in vaccinated flounder. These results demonstrated that rOmpV co-vaccination with rIFN-γ or pcIFN-γ could both boost the immune responses and evoke highly protective effects against E. tarda, indicating that flounder IFN-γ is a promising adjuvant candidate for fish vaccination via an injection administering route.

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.

Site Directed Disulfide PEGylation of Interferon-β-1b with Fork Peptide Linker

The attachment of PEG to biopharmaceuticals has been applied for enhancement of bioavailability and improved stability. The PEG polymer is highly hydrated; thus effective attachment to inaccessible sites could be hindered. We have devised a scheme to address this issue by introducing a considerable distance between PEG and protein by addition of a linear peptide, appended to long chained reactive linkers. Second, the position of PEG conjugation directly affects biological activity. Accordingly, a disulfide bond could be considered as an ideal choice for site directed PEGylation; but reactivity of both thiol moieties to bridging reagent is critical for maintenance of protein structure. In our design, a forked structure with two arms provides essential flexibility to account for dissociation of reduced cysteines. An efficient yield for disulfide PEGylation of IFN-β1b was attained and specificity, biophysical characterization, biological activity, and pharmacokinetics were surveyed.

Chemically Crosslinked Bispecific Antibodies for Cancer Therapy: Breaking from the Structural Restrictions of the Genetic Fusion Approach

Antibodies are composed of structurally and functionally independent domains that can be used as building blocks to construct different types of chimeric protein-format molecules. However, the generally used genetic fusion and chemical approaches restrict the types of structures that can be formed and do not give an ideal degree of homogeneity. In this study, we combined mutation techniques with chemical conjugation to construct a variety of homogeneous bivalent and bispecific antibodies. First, building modules without lysine residues—which can be chemical conjugation sites—were generated by means of genetic mutation. Specific mutated residues in the lysine-free modules were then re-mutated to lysine residues. Chemical conjugation at the recovered lysine sites enabled the construction of homogeneous bivalent and bispecific antibodies from block modules that could not have been so arranged by genetic fusion approaches. Molecular evolution and bioinformatics techniques assisted in finding viable alternatives to the lysine residues that did not deactivate the block modules. Multiple candidates for re-mutation positions offer a wide variety of possible steric arrangements of block modules, and appropriate linkages between block modules can generate highly bioactive bispecific antibodies. Here, we propose the effectiveness of the lysine-free block module design for site-specific chemical conjugation to form a variety of types of homogeneous chimeric protein-format molecule with a finely tuned structure and function.

THETA system allows one-step isolation of tagged proteins through temperature-dependent protein-peptide interaction

Tools to control protein-protein interactions by external stimuli have been extensively developed. For this purpose, thermal stimulation can be utilized in addition to light. In this study, we identify a monoclonal antibody termed C13 mAb, which shows an approximately 480-fold decrease in the affinity constant at 37 °C compared to that at 4 °C. Next, we apply this temperature-dependent protein-peptide interaction for one-step protein purifications. We term this THermal-Elution-based TAg system as the THETA system, in which gel-immobilized C13 mAb-derived single-chain variable fragment (scFv) (termed THETAL) is able to bind with proteins tagged by C13 mAb-epitope(s) (THETAS) at 4 °C and thermally release at 37-42 °C. Moreover, to reveal the temperature-dependent interaction mechanism, molecular dynamics simulations are performed along with epitope mapping experiments. Overall, the high specificity and reversibility of the temperature-dependent features of the THETA system will support a wide variety of future applications such as thermogenetics.

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

Single-chain variable fragment (scFv) has great prospect in medical therapies and diagnostic applications due to its binding affinity and low immunogenicity. However, the application of scFv is limited by its heterologous expression facing challenges of insoluble aggregation. sfGFP has been developed as fusion tag to facilitate the solubility of fusion partner in Escherichia coli. We designed fusion protein of anti-influenza PB2 scFv at C-terminus of sfGFP and successfully obtained soluble expression of sfGFP-scFv-His in Escherichia coli. The expression level of sfGFP-scFv-His reached at 20 mg/L of bacterial culture when the culture was induced with 0.1 mM IPTG at 18 °C for 16 h. And 6 mg scFv-His was obtained from the cleavage of 10 mg pure sfGFP-scFv-His with TEV protease. In addition, we found that sfGFP-scFv-His was more stable than scFv-His in chicken serum, suggesting that sfGFP not only facilitated the solubility of scFv in Escherichia coli, but also promoted the stability of scFv. The immunologic activity of sfGFP-scFv-His was confirmed by Western blot and ELISA; the results showed that anti-PB2 sfGFP-scFv-His exhibited specific binding to PB2. Hemagglutination and comparative real-time RT-PCR analysis indicated that sfGFP-scFv-His and scFv-His inhibited the replication of H1N1 influenza virus in the infected A549 cells. These results further develop the application of scFv as an agent, such as anti-influenza. Furthermore, soluble expression of scFv using sfGFP as fusion partner provide a cost-effective preparation model for manufacturing scFv against pandemic disease.

Modification of the first constant domain of heavy chain enabled effective folding of functional anti-forskolin antigen-binding fragment for sensitive quantitative analysis

The assembly between heavy and light chains is a critical step of immunoglobulin (Ig) and fragment antigen-binding (Fab) antibody expression and of their binding activity. The genes encoding Fab were obtained from hybridoma cells secreting monoclonal antibody (MAb, IgG2b) against adenylate cyclase activator forskolin (FOR). The subclass of the first constant domain of heavy chain (C_H 1) of IgG2b was modified to IgG1 via overlap extension polymerase chain reaction and expressed via Escherichia coli bacterial system. Since both Fabs (IgG2b and IgG1) were expressed as inclusion bodies, functional analysis was performed after in vitro refolding via stepwise dialysis. The result indicated that the folding efficiency between V_H -C_H 1 and V_L -C_L was improved by the C_H 1 modification from IgG2b to IgG1 subclass, although their specificity for FOR was not altered. Effective folding of IgG1 was also observed when they were expressed in the hemolymph of silkworm larvae using the Bombyx mori nuclear polyhedrosis virus bacmid system. An indirect competitive enzyme-linked immunosorbent assay (icELISA) was then developed for the determination of FOR using effectively prepared Fab IgG1. The sensitivity of FOR determination was in the range of 3.91-62.5 ng/mL with less than 9% relative standard deviation, implying the sensitive and reliable analysis of developed icELISA. In addition, high accuracy of the icELISA was supported by the results of spiked-and-recovery tests, ranging from 100.2 to 102.3%. Therefore, Fab could be utilized reliably for icELISA instead of the more expensive MAb. Collectively, this approach improved productivity of Fab and reduced the cost of antibody production.

Test bacterial inclusion body for activity prior to start denaturing and refolding processes to obtain active eukaryotic proteins

One of a major drawbacks correlated with expressing antibody fragments in bacterial cells is insolubility, which is often regarded as an obstacle in obtaining active molecules. Recombinant proteins aggregated as inclusion bodies within bacterial cells are thought to be unfolded or misfolded, and therefore inactive. So, denaturing and refolding strategies, which are laborious and sometime inefficient, are used to obtain correctly-folded active proteins. In the current study, we show that large quantities of correctly folded and completely active scFv molecules are there in bacterial inclusion bodies; they only need to be isolated from inclusion bodies.

Development of a fluvoxamine detection system using a Quenchbody, a novel fluorescent biosensor

The misuse of psychotropic drugs intended for medical treatment represents a recent worldwide public health concern. Quenchbody (Q-body) is a novel fluoroimmunosensor that can detect an antigen immediately without additional reagents or washing steps. Here, we describe creating Q-bodies for the detection of the antidepressant fluvoxamine (FLV) and determining optimal conditions to achieve the highest fluorescence intensity (FI). We prepared five Q-bodies with the fluorophore labeled at either the N- or C- terminus and with different linker lengths. Fluorescence was measurable within minutes, indicating the interaction of Q-bodies with FLV. The normalized FI (FI ratio) of the N-terminus labeled Q-body increased approximately 1.5-fold upon FLV addition; Q-bodies labeled at the C-terminus did not significantly increase FI. Among the fluorescence dyes used in this study, Rhodamine 6G labeled Q-body showed the best FI ratio. EC₅₀ values of the N-terminus labeled Q-bodies were similar (23.2-224nM) regardless of linker length or labeling dye. We examined whether the Q-body could be applicable to serum matrix instead of phosphate-buffered saline. The intact serum interfered strongly with the Q-body fluorescence. However, the FI ratios of the Q-body for FLV-spiked serum filtrate, for which proteins were removed by filtration, showed a dose-dependency for detecting FLV levels. Deproteinization, which does not interfere with Q-body fluorescence measurements, is likely necessary to detect serum FLV with high sensitivity. This study demonstrates the potential of Q-body probes as a tool towards developing creative immunoassay applications.

Modeling, simulation, and employing dilution-dialysis microfluidic chip (DDMC) for heightening proteins refolding efficiency

Miniaturized systems based on the principles of microfluidics are widely used in various fields, such as biochemical and biomedical applications. Systematic design processes are demanded the proper use of these microfluidic devices based on mathematical simulations. Aggregated proteins (e.g., inclusion bodies) in solution with chaotropic agents (such as urea) at high concentration in combination with reducing agents are denatured. Refolding methods to achieve the native proteins from inclusion bodies of recombinant protein relying on denaturant dilution or dialysis approaches for suppressing protein aggregation is very important in the industrial field. In this paper, a modeling approach is introduced and employed that enables a compact and cost-effective method for on-chip refolding process. The innovative aspect of the presented refolding method is incorporation dialysis and dilution. Dilution-dialysis microfluidic chip (DDMC) increases productivity folding of proteins with the gradual reduction of the amount of urea. It has shown the potential of DDMC for performing refolding of protein trials. The principles of the microfluidic device detailed in this paper are to produce protein on the dilution with slow mixing through diffusion of a denatured protein solution and stepwise dialysis of a refolding buffer flowing together and the flow regime is creeping flow. The operation of DDMC was modeled in two dimensions. This system simulated by COMSOL Multiphysics Modeling Software. The simulation results for a microfluidic refolding chip showed that DDMC was deemed to be perfectly suitable for control decreasing urea in the fluid model. The DDMC was validated through an experimental study. According to the results, refolding efficiency of denaturant Hen egg white lysozyme (HEWL) (EC 3.2.1.17) used as a model protein was improved. Regard to the remaining activity test, it was increased from 42.6 in simple dilution to 93.7 using DDMC.

Characterization of plasma labile heme in hemolytic conditions

Extracellular hemoglobin, a byproduct of hemolysis, can release its prosthetic heme groups upon oxidation. This produces metabolically active heme that is exchangeable between acceptor proteins, macromolecules and low molecular weight ligands, termed here labile heme. As it accumulates in plasma labile heme acts in a pro‐oxidant manner and regulates cellular metabolism while exerting pro‐inflammatory and cytotoxic effects that foster the pathogenesis of hemolytic diseases. Here, we developed and characterized a panel of heme‐specific single domain antibodies (sdAbs) that together with a cellular‐based heme reporter assay, allow for quantification and characterization of labile heme in plasma during hemolytic conditions. Using these approaches, we demonstrate that when generated during hemolytic conditions labile heme is bound to plasma molecules with an affinity higher than 10⁻⁷m and that 2–8% (~ 2–5 μm) of the total amount of heme detected in plasma can be internalized by bystander cells, termed here bioavailable heme. Acute, but not chronic, hemolysis is associated with transient reduction of plasma heme‐binding capacity, that is, the ability of plasma molecules to bind labile heme with an affinity higher than 10⁻⁷m. The heme‐specific sdAbs neutralize the pro‐oxidant activity of soluble heme in vitro, suggesting that these maybe used to counter the pathologic effects of labile heme during hemolytic conditions. Finally, we show that heme‐specific sdAbs can be used to visualize cellular heme. In conclusion, we describe a panel of heme‐specific sdAbs that when used with other approaches provide novel insights to the pathophysiology of heme.

Microbial Carbonic Anhydrases in Biomimetic Carbon Sequestration for Mitigating Global Warming: Prospects and Perspectives

All the leading cities in the world are slowly becoming inhospitable for human life with global warming playing havoc with the living conditions. Biomineralization of carbon dioxide using carbonic anhydrase (CA) is one of the most economical methods for mitigating global warming. The burning of fossil fuels results in the emission of large quantities of flue gas. The temperature of flue gas is quite high. Alkaline conditions are necessary for CaCO3 precipitation in the mineralization process. In order to use CAs for biomimetic carbon sequestration, thermo-alkali-stable CAs are, therefore, essential. CAs must be stable in the presence of various flue gas contaminants too. The extreme environments on earth harbor a variety of polyextremophilic microbes that are rich sources of thermo-alkali-stable CAs. CAs are the fastest among the known enzymes, which are of six basic types with no apparent sequence homology, thus represent an elegant example of convergent evolution. The current review focuses on the utility of thermo-alkali-stable CAs in biomineralization based strategies. A variety of roles that CAs play in various living organisms, the use of CA inhibitors as drug targets and strategies for overproduction of CAs to meet the demand are also briefly discussed.

Determination of immune status in dogs against CPV-2 by recombinant protein based latex agglutination test

Canine parvoviral enteritis is a highly contagious viral illness caused by canine parvovirus-2 (CPV-2) which affects puppies of mainly 6-20 weeks of age. Vaccination is pivotal in preventing and controlling CPV-2 infection. Determination of antibody status is a critical determinant for successful vaccination. The hemagglutination inhibition (HI) test is 'gold standard' test for quantification of antibodies specific to CPV-2, although the execution of this test is not feasible under field conditions. The present study was undertaken to develop a point of care testing to determine immune status prior to CPV-2 vaccination or to detect seroconversion in immunized dogs by latex agglutination test (LAT) using recombinant antigen. Truncated portion of VP2 protein (tVP2) of CPV-2 was selected on the basis of antigenic indices, overexpressed the recombinant protein in E. coli system and was subsequently used in development of LAT. A total of 59 serum samples obtained from vaccinated (n = 54) and healthy unvaccinated (n = 5) dogs were tested. The positivity was observed in 85% (46/54) of these dogs with varying agglutination pattern. The overall sensitivity and specificity of latex agglutination test in comparison to HI test was recorded as 90% and 88% respectively with an agreement value of 90% (CI = 95%).

The Immune Adjuvant Effects of Flounder (Paralichthys olivaceus) Interleukin-6 on E. tarda Subunit Vaccine OmpV

Interleukin-6 (IL-6) as a pleiotropic cytokine was widely used as an effective adjuvant for vaccines in mammals. In this study, the immune adjuvant effects of two forms of flounder (Paralichthys olivaceus) IL-6, including recombinant IL-6 (rIL-6) and pcDNA3.1-IL-6 (pcIL-6), were evaluated and comparatively analyzed on E. tarda subunit vaccine recombinant outer membrane protein V (rOmpV). The results showed that the relative percent survivals of flounder vaccinated with rOmpV plus rIL-6 or pcIL-6 were significantly higher than that in the two control groups, rOmpV plus recombinant 6× histidine-tag (rHis) or empty expression vector pcDNA3.1 (pcN3). The levels of specific serum antibodies and surface membrane immunoglobulin-positive (sIg+) lymphocytes in peripheral blood, spleen, and head kidney in the two adjuvant groups were also much higher than that in the two control groups. Compared with the two control groups, higher upregulated expressions of major histocompatibility complex class Iα (MHCIα), cluster of differentiation 8α (CD8α), MHCIIα, CD4-1, interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) were detected in flounder vaccinated with rOmpV plus rIL-6 or pcIL-6 after challenge. In addition, the rOmpV plus rIL-6 could induce significant higher levels of specific serum antibodies, sIg+ lymphocytes and four genes expressions than rOmpV plus pcIL-6. These results demonstrated that both rIL-6 and pcIL-6 used as adjuvants could enhance the immune response and evoke immune protections against E. tarda infection, which has a significant value in controlling diseases using vaccines in flounder.

An overview and comparison of a recombinant antigen-binding fragment and an antigen-binding fragment from a monoclonal antibody against wogonin glucuronide

Wogonin glucuronide (wogonin 7-O-β-D-glucuronide, Wgn) is widely recognized as a constituent of Scutellariae radix, which is used in Kampo medicines. Wgn has been used for both pharmacological (antifebrile uses and in detoxification) and research purposes. A recombinant antigen-binding fragment (rFab) and an antigen-binding fragment from a monoclonal antibody (mFab) against Wgn were constructed and used in an indirect competitive enzyme-linked immunosorbent assay (icELISA) in this study. The rFab and mFab against Wgn showed both activity and recognition against Wgn. The developed icELISA was validated as a quantitative analytical method to detect Wgn by testing both its utility and its reliability using multiple concentrations of Wgn from S. radix. This approach provides a more economic method to analyze and purify Kampo medicines.

Arginine prevents thermal aggregation of hen egg white proteins

The control of aggregation and solubilization of hen egg white protein (HEWP) is an important issue for industrial applications of one of the most familiar food protein sources. Here, we investigated the effects of edible amino acids on heat-induced aggregation of HEWP. The addition of 0.6M arginine (Arg) completely suppressed the formation of insoluble aggregates of 1mgmL^-1 HEWP following heat treatment, even at 90°C for 20min. In contrast, lysine (Lys), glycine (Gly), and sodium chloride (NaCl) did little to suppress the aggregation of HEWP under the same conditions. SDS-PAGE indicated that Arg suppresses the thermal aggregation of almost all types of HEWP at 1mgmL^-1. However, Arg did not suppress the thermal aggregation of HEWP at concentrations ≥10mgmL^-1 and prompted the formation of aggregates. Transmission electron micrographs revealed a high-density structure of unfolded proteins in the presence of Arg. These results indicate that Arg exerts a greater suppressive effect on a protein mixture, such as HEWP, than on a single model protein. These observations may propose Arg as a safe and reasonable additive to HEWP for the elimination of microorganisms by allowing an increase in sterilization temperature.

Computational de novo design of antibodies binding to a peptide with high affinity

Antibody drugs play a critical role in infectious diseases, cancer, autoimmune diseases, and inflammation. However, experimental methods for the generation of therapeutic antibodies such as using immunized mice or directed evolution remain time consuming and cannot target a specific antigen epitope. Here, we describe the application of a computational framework called OptMAVEn combined with molecular dynamics to de novo design antibodies. Our reference system is antibody 2D10, a single-chain antibody (scFv) that recognizes the dodecapeptide DVFYPYPYASGS, a peptide mimic of mannose-containing carbohydrates. Five de novo designed scFvs sharing less than 75% sequence similarity to all existing natural antibody sequences were generated using OptMAVEn and their binding to the dodecapeptide was experimentally characterized by biolayer interferometry and isothermal titration calorimetry. Among them, three scFvs show binding affinity to the dodecapeptide at the nM level. Critically, these de novo designed scFvs exhibit considerably diverse modeled binding modes with the dodecapeptide. The results demonstrate the potential of OptMAVEn for the de novo design of thermally and conformationally stable antibodies with high binding affinity to antigens and encourage the targeting of other antigen targets in the future. Biotechnol. Bioeng. 2017;114: 1331-1342. © 2017 Wiley Periodicals, Inc.

Production and Purification of a Novel Anti-TNF-α Single Chain Fragment Variable Antibody

PURPOSE

TNF-α is an inflammatory cytokine with a key role in initiation of inflammatory responses. Anti-TNF-α antibodies are being used in clinic for the purpose of diagnosis and treatment due to their high specificity. The objective of the current study was to express and purify an anti-TNF-α scFv antibody identified by phage display technology.

METHODS

The DNA coding sequence of the identified scFv was cloned into pET28a vector and the corresponding protein was expressed as 6×His tagged using E.coli BL21 (DE3) pLysS expression system followed by affinity purification on Ni-Sepharose affinity column.

RESULTS

The J44 scFv antibody was cloned into the expression vector and successfully expressed and purified. The purity of the scFv fraction was confirmed using SDS-PAGE analysis. Western blotting technique was used to detect expression of 6×His tagged protein.

CONCLUSION

In the current study an anti-TNF-α scFv antibody was successfully expressed in bacterial expression system and purified on affinity column. The purified protein can be used in different in vitro and in vivo experiments in order to elucidate its functionality.

Isolation of soluble scFv antibody fragments specific for small biomarker molecule, L-Carnitine, using phage display

Isolation of single chain antibody fragment (scFv) clones from naïve Tomlinson I+J phage display libraries that specifically bind a small biomarker molecule, L-Carnitine, was performed using iterative affinity selection procedures. L-Carnitine has been described as a conditionally essential nutrient for humans. Abnormally high concentrations of L-Carnitine in urine are related to many health disorders including diabetes mellitus type 2 and lung cancer. ELISA-based affinity characterization results indicate that selectants preferentially bind to L-Carnitine in the presence of key bioselecting component materials and closely related L-Carnitine derivatives. In addition, the affinity results were confirmed using biophysical fluorescence quenching for tyrosine residues in the V segment. Small-scale production of the soluble fragment yielded 1.3mg/L using immunopure-immobilized protein A affinity column. Circular Dichroism data revealed that the antibody fragment (Ab) represents a folded protein that mainly consists of β-sheets. These novel antibody fragments may find utility as molecular affinity interface receptors in various electrochemical biosensor platforms to provide specific L-Carnitine binding capability with potential applications in metabolomic devices for companion diagnostics and personalized medicine applications. It may also be used in any other biomedical application where detection of the L-Carnitine level is important.

Single Chain Variable Fragments Produced in Escherichia coli against Heat-Labile and Heat-Stable Toxins from Enterotoxigenic E. coli

BACKGROUND

Diarrhea is a prevalent pathological condition frequently associated to the colonization of the small intestine by enterotoxigenic Escherichia coli (ETEC) strains, known to be endemic in developing countries. These strains can produce two enterotoxins associated with the manifestation of clinical symptoms that can be used to detect these pathogens. Although several detection tests have been developed, minimally equipped laboratories are still in need of simple and cost-effective methods. With the aim to contribute to the development of such diagnostic approaches, we describe here two mouse hybridoma-derived single chain fragment variable (scFv) that were produced in E. coli against enterotoxins of ETEC strains.

METHODS AND FINDINGS

Recombinant scFv were developed against ETEC heat-labile toxin (LT) and heat-stable toxin (ST), from previously isolated hybridoma clones. This work reports their design, construction, molecular and functional characterization against LT and ST toxins. Both antibody fragments were able to recognize the cell-interacting toxins by immunofluorescence, the purified toxins by ELISA and also LT-, ST- and LT/ST-producing ETEC strains.

CONCLUSION

The developed recombinant scFvs against LT and ST constitute promising starting point for simple and cost-effective ETEC diagnosis.

High-yield reactivation of anionic tobacco peroxidase overexpressed in Escherichia coli

Anionic tobacco peroxidase (TOP) is extremely active in chemiluminescence reaction of luminol oxidation without addition of enhancers and more stable than horseradish peroxidase under antibody conjugation conditions. In addition, recombinant TOP (rTOP) produced in Escherichia coli is known to be a perfect direct electron transfer catalyst on electrodes of various origin. These features make the task of development of a high-yield reactivation protocol for rTOP practically important. Previous attempts to reactivate the enzyme from E. coli inclusion bodies were successful, but the reported reactivation yield was only 14%. In this work, we thoroughly screened the refolding conditions for dilution protocol and compared it with gel-filtration chromatography. The impressive reactivation yield in the dilution protocol (85%) was achieved for 8 μg/mL solubilized rTOP protein and the refolding medium containing 0.3 mM oxidized glutathione, 0.05 mM dithiothreitol, 5 mM CaCl2, 5% glycerol in 50 mM Tris-HCl buffer, pH 9.6, with 1 μM hemin added at the 24th hour of incubation. A practically important discovery was a 30-40% increase in the reactivation yield upon delayed addition of hemin. The reactivation yield achieved is one of the highest reported in the literature on protein refolding by dilution. The final yield of purified active non-glycosylated rTOP was ca. 60 mg per L of E. coli culture, close to the yield reported before for tomato and tobacco plants overexpressing glycosylated TOP (60 mg/kg biomass) and much higher than for the previously reported refolding protocol (2.6 mg per L of E. coli culture).

Effect of charged amino acid side chain length on lateral cross-strand interactions between carboxylate- and guanidinium-containing residues in a β-hairpin

β-Sheet is one of the major protein secondary structures. Oppositely charged residues are frequently observed across neighboring strands in antiparallel sheets, suggesting the importance of cross-strand ion pairing interactions. The charged amino acids Asp, Glu, Arg, and Lys have different numbers of hydrophobic methylenes linking the charged functionality to the backbone. To investigate the effect of side chain length of guanidinium- and carboxylate-containing residues on lateral cross-strand ion pairing interactions at non-hydrogen-bonded positions, β-hairpin peptides containing Zbb-Agx (Zbb = Asp, Glu, Aad in increasing length; Agx = Agh, Arg, Agb, Agp in decreasing length) sequence patterns were studied by NMR methods. The fraction folded population and folding energy were derived from the chemical shift deviation data. Peptides with high fraction folded populations involved charged residue side chain lengths that supported high strand propensity. Double mutant cycle analysis was used to determine the interaction energy for the potential lateral ion pairs. Minimal interaction was observed between residues with short side chains, most likely due to the diffused positive charge on the guanidinium group, which weakened cross-strand electrostatic interactions with the carboxylate side chain. Only the Aad-Arg/Agh interactions with long side chains clearly exhibited stabilizing energetics, possibly relying on hydrophobics. A survey of a non-redundant protein structure database revealed that the statistical sheet pair propensity followed the trend Asp-Arg < Glu-Arg, implying the need for matching long side chains. This suggested the need for long side chains on both guanidinium-bearing and carboxylate-bearing residues to stabilize the β-hairpin motif.

Microfluidic chips with multi-junctions: an advanced tool in recovering proteins from inclusion bodies

Active recombinant proteins are used for studying the biological functions of genes and for the development of therapeutic drugs. Overexpression of recombinant proteins in bacteria often results in the formation of inclusion bodies, which are protein aggregates with non-native conformations. Protein refolding is an important process for obtaining active recombinant proteins from inclusion bodies. However, the conventional refolding method of dialysis or dilution is time-consuming and recovered active protein yields are often low, and a cumbersome trial-and-error process is required to achieve success. To circumvent these difficulties, we used controllable diffusion through laminar flow in microchannels to regulate the denaturant concentration. This method largely aims at reducing protein aggregation during the refolding procedure. This Commentary introduces the principles of the protein refolding method using microfluidic chips and the advantage of our results as a tool for rapid and efficient recovery of active recombinant proteins from inclusion bodies.

A screening methodology for purifying proteins with aggregation problems

Many proteins are prone to aggregate or insoluble for different reasons. This poses an extraordinary challenge at the expression level, but even more during downstream purification processes. Here we describe a strategy that we developed for purifying prone-to-aggregate proteins. Our methodology can be easily implemented in small laboratories without the need for automated, expensive platforms. This procedure is especially suitable for intrinsically disordered proteins (IDPs) and for proteins with intrinsically disordered regions (IDRs). Such proteins are likely to aggregate due to their lack of tertiary structure and their extended and flexible conformations. Similar methodologies can be applied to other proteins with comparable tendency to aggregate during the expression or purification steps. In this chapter, we will mainly focus on protein solubility and stability issues during purification and storage, on factors that can prevent aggregation or maintain solubility, and on the importance of the early elimination of aggregates during protein purification.

Expression of V(H)-linker-V(L) orientation-dependent single-chain Fv antibody fragment derived from hybridoma 2E6 against aflatoxin B1 in Escherichia coli

Aflatoxin B1 (AFB1) is a toxic secondary metabolic product, which threatens human and animal health. Antibody is a key factor for immunoassay against toxic stuff like AFB1, and single-chain Fv antibody fragment (scFv) has become a popular format of genetically engineered antibody. In this study, four hybridoma cell lines against AFB1 were obtained, and then scFvs 2E6 derived from hybridoma cell line 2E6 were constructed in different V(H)/V(L) orientations. Subsequently, scFvs 2E6 were expressed in E. coli BL21(DE3) mainly in the form of inclusion body. SDS-PAGE, Western blot and ELISA were employed to characterize scFvs 2E6. The results revealed that the yield of inclusion body of scFvs 2E6 in either V(H)/V(L) orientation was similar; however, only the scFv in V(H)-linker-V(L) orientation showed anti-AFB1 bioactivity after refolding. The present study underscores the importance of choosing optimal V(H)/V(L) orientation for scFv construction, and scFv may be favorable for immunoassays in food industry.

Refolded scFv antibody fragment against myoglobin shows rapid reaction kinetics

Myoglobin is one of the early biomarkers for acute myocardial infarction. Recently, we have screened an antibody with unique rapid reaction kinetics toward human myoglobin antigen. Antibodies with rapid reaction kinetics are thought to be an early IgG form produced during early stage of in vivo immunization. We produced a recombinant scFv fragment for the premature antibody from Escherichia coli using refolding technology. The scFv gene was constructed by connection of the V(H)-V(L) sequence with a (Gly4Ser)3 linker. The scFv fragment without the pelB leader sequence was expressed at a high level, but the solubility was extremely low. A high concentration of 8 M urea was used for denaturation. The dilution refolding process in the presence of arginine and the redox reagents GSH and GSSH successfully produced a soluble scFv protein. The resultant refolded scFv protein showed association and dissociation values of 9.32 × 10⁻⁴ M⁻¹·s⁻¹ and 6.29 × 10⁻³ s⁻¹, respectively, with an affinity value exceeding 10⁷ M⁻¹ (k(on)/k(off)), maintaining the original rapid reaction kinetics of the premature antibody. The refolded scFv could provide a platform for protein engineering for the clinical application for diagnosis of heart disease and the development of a continuous biosensor.

Purification and refolding of anti-T-antigen single chain antibodies (scFvs) expressed in Escherichia coli as inclusion bodies

T-antigen (Galβ1-3GalNAcα-1-Ser/Thr) is an oncofetal antigen that is commonly expressed as a carbohydrate determinant in many adenocarcinomas. Since it is associated with tumor progression and metastasis, production of recombinant antibodies specific for T-antigen could lead to the development of cancer diagnostics and therapeutics. Previously, we isolated and characterized 11 anti-T-antigen phage clones from a phage library displaying human single-chain antibodies (scFvs) and purified one scFv protein, 1G11. More recently, we purified and characterized 1E8 scFv protein using a Drosophila S2 expression system. In the current study, four anti-T-antigen scFv genes belonging to Groups 1-4 were purified from inclusion bodies expressed in Escherichia coli cells. Inclusion bodies isolated from E. coli cells were denatured in 3.5 M Gdn-HCl. Solubilized His-tagged scFv proteins were purified using Ni(2+)-Sepharose column chromatography in the presence of 3.5 M Gdn-HCl. Purified scFv proteins were refolded according to a previously published method of step-wise dialysis. Two anti-T-antigen scFv proteins, 1E6 and 1E8 that belong to Groups 1 and 2, respectively, were produced in sufficient amounts, thus allowing further characterization of their binding activity with T-antigen. Specificity and affinity constants determined using enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR), respectively, provided evidence that both 1E8 and 1E6 scFv proteins are T-antigen specific and suggested that 1E8 scFv protein has a higher affinity for T-antigen than 1E6 scFv protein.

Production and characterization of single-chain antibody (scFv) against 3ABC non-structural protein in Escherichia coli for sero-diagnosis of Foot and Mouth Disease virus

Differentiation of Foot-and-Mouth Disease infected from vaccinated animals is essential for effective implementation of vaccination based control programme. Detection of antibodies against 3ABC non-structural protein of FMD virus by immunodiagnostic assays provides reliable indication of FMD infection. Sero-monitoring of FMD in the large country like India is a big task where thousands of serum samples are annually screened. Currently, monoclonal or polyclonal antibodies are widely used in these immunodiagnostic assays. Considering the large population of livestock in the country, an economical and replenishable alternative of these antibodies was required. In this study, specific short chain variable fragment (scFv) antibody against 3B region of 3ABC poly-protein was developed. High level of scFv expression in Escherichia coli system was obtained by careful optimization in four different strains. Two formats of enzyme immunoassays (sandwich and competitive ELISAs) were optimized using scFv with objective to differentiate FMD infected among the vaccinated population. The assays were statistically validated by testing 2150 serum samples. Diagnostic sensitivity/specificity of sandwich and competitive ELISAs were determined by ROC method as 92.2%/95.5% and 89.5%/93.5%, respectively. This study demonstrated that scFv is a suitable alternate for immunodiagnosis of FMD on large scale.

GFP-SCFV: expression and possible applications as a tool for experimental investigations of atherosclerosis

Experimental studies on atherosclerosis are crucial for investigating its pathophysiology, defining new therapeutic targets, and developing new drugs and diagnostic tools. Thus, many imaging markers have been developed and introduced in experimental studies. The main advantage of these new tools is that they allow the noninvasive diagnosis of atherosclerotic vascular disease. Here, we describe the cloning, expression, purification, and stabilization of a chimeric protein specifically designed to probe cells and tissues for the presence of LDL(-), a relevant marker of atherosclerosis. The DNA sequence that encodes the anti-LDL(-) scFv, previously obtained from a hybridoma secreting an anti-LDL(-) monoclonal antibody, was inserted into the bacterial vector pET-28a(+) in tandem with a DNA sequence encoding GFP. The recombinant protein was expressed in high yields in E. coli as inclusion bodies. The applicability of GFP-scFv was assessed by ELISA, which determined its affinity for LDL(-) and confocal microscopy, that showed macrophage uptake of the protein along with LDL(-). In conclusion, our data suggest that the anti-LDL(-) GFP-scFv chimeric protein could be useful in studies on atherogenesis as well as for developing diagnostic tools for atherosclerosis.

Efficient refolding and immobilization of PMMA-tag-fused single-chain Fv antibodies for sensitive immunological detection on a PMMA plate

In this study, we investigated the efficient refolding and site-specific immobilization of single-chain variable fragments (scFvs) genetically fused with a poly(methylmethacrylate)-binding peptide (PMMA-tag). According to the results of an aggregation test of a scFv-PM in the presence of 0.5 M urea, aggregation was hardly detectable at a weak-alkaline pH (8.5) with lower concentrations of NaCl. Consequently, more than 93% recovery of the anti-RNase scFv-PM model was attained, when it was refolded by dialysis against 50 mM TAPS (pH8.5). These results suggested that the apparent isoelectric point (pI) of a target scFv was decreased to a great extent by the genetic fusion of a PMMA-tag containing 5 acidic amino acids, and, thus, the solubility of the scFv-PM in its semi-denatured form was considerably improved. We also designed alternative peptide-tags composed of plural aspartic acid residues (D5, D10 and D15-tags) to decrease the apparent pI value of the fusion protein. As a consequence, scFv-D5, scFv-D10 and scFv-D15 were also efficiently refolded with yields of more than 95%. It is noteworthy that even scFv-PS-D15, which had both a positively charged polystyrene-binding peptide (PS-tag) and a negatively charged D15-tag, was serially connected at the C-terminal region of scFvs, and also refolded with a yield of 96.1%. These results clearly indicate that controlling the apparent pI value of scFvs by the fusion of oligo-peptides composed of acidic amino acids at the C-terminus resulted in a high degree of recovery via dialysis refolding. According to the results of a sandwich ELISA using scFv-PMs, scFv-D15 and scFv-PS-D15 as ligands, high antigen-binding signals were detected from both the PMMA and phi-PS plates immobilized with scFv-PMs. Furthermore, the high antigen-binding activity of scFv-PMs was maintained in an adsorption state when it was immobilized on the surface of not only PMMA, but also hydrophilic PS (phi-PS) and polycarbonate (PC). These results strongly suggested that a PMMA-tag introduced at the C-terminus of scFvs preferably recognizes ester and/or carboxyl groups exposed on the surface of plastics. The scFv-PM developed in the present study has advantages such as being a ligand antibody, compared with whole Ab and the conventional PS-tag-fused scFvs (scFv-PS), and, thus, it is considerably useful in a sandwich ELISA as well as in various immuno-detection and immuno-separation systems.